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Soft Functional Polynuclear Coordination Compounds Containing Pyrimidine Bridges
Abstract
In this account, we describe the use of simple pyrimidine derivatives in combination with metal ions to build highly structured molecular architectures containing functional nanoenvironments, cavities and surfaces that can interact with additional species. The supramolecular structure of these systems can be rationally controlled by metal fragment geometry, reaction conditions and presence of templating agents. Thus, the use of transition metals with low coordination numbers or blocked bonding positions in combination with pyrimidines (e.g. 2-hydroxypyrimidine, 4-hydroxypyrimidine, 2,4-dihydroxypyrimidine, 2-aminopyrimidine) leads to the formation of either discrete assemblies, 1D polymers or helixes. When metal ions with higher coordination possibilities are applied instead, 2D and 3D networks are generated. Some of the assemblies built in this way possess functional cavities, pores and surfaces that can interact with additional species by means of hydrophobic, electrostatic, H-bonding interactions and coordinative bonds to give rise to recognition processes. The latter range from molecular recognition in homogeneous phase as well as clathrate formation, to heterogeneous solid–gas and solid–liquid adsorption phenomena. It should be noted that these materials are not rigid but able to undergo guest-induced reorganisation processes even in the solid state. Finally, some of these materials also combine additional interesting magneto-optical properties. Thus, dual systems can be envisaged in which two or more of these properties are present in the same material.
... Several papers on metallacycles based on N-heterocycles and nucleobases, including those called metallacalixarenes, have been reported [19][20][21][22][23][24][25]. ...
... Numerous metallacalixarenes based on heterocycles can be found in the literature [20][21][22]25]. They are easily obtained in the reaction of a cis-protected metal fragment, such as Pd 2+ or Pt 2+ complexes, with an appropriate N-heterocyclic ligand having two ligating nitrogen atoms forming an angle of 120 • as in the structures of pyridine, pyrimidine, 4,7-phenanthroline and 2,2 -bipyrazine derivatives or 150 • as in the imidazole ring. ...
... Pyrimidine and its derivatives (Fig. 18) have attracted much attention as organic linkers for the synthesis of metallacalixarenes [20][21][22][39][40][41][42][43][44][45]. A class of so-called "platinum pyrimidine blues" is a very promising group of materials for antitumor agents. ...
This review focuses on the synthesis and applications of organic–inorganic hybrid materials called metallacalixarenes. Two different subclasses of metallacalixarenes are presented: cyclic discrete oligomers based on heterocycles or nucleobases and metallacalixarenes as part of a polymeric network based on 1,3-dicarboxylate ligands. In addition to their potential application in gas adsorption/separations, magnetism and catalysis, metallacalixarenes might complex cations, anions, or neutral molecules due to their calixarene-like cavities.
... Like their organic analogues, these systems are able to give a rich variety of host-guest interactions, which include metal-ion, anion and ion-pair recognition. [5] In this regard, we and others have shown that their cationic nature leads to a concomitant high affinity for Abstract: A set of cyclic tetranuclear complexes of the metallacalix [4]arene type with formula [{Pt(en)(L)} 4 ] 4 + (en = ethylenediamine; 2: LH= 5chloro-2-hydroxypyrimidine (5-Cl-Hpymo); 3: LH= 5-bromo-2-hydroxypyrimidine (5-Br-Hpymo); 4: LH= 5iodo-2-hydroxypyrimidine (5-I-Hpymo)) have been obtained from the reaction between cis-protected squareplanar [Pt(en)A C H T U N G T R E N N U N G (H 2 O) 2 ] 2 + metal entities and LH in aqueous media. Additionally, the binding properties of 2, 3, 4 and their congener [{Pt(en)(L)} 4 ] 4 + (1: LH = 2-hydroxypyrimidine (Hpymo)) with calf thymus-DNA (ct-DNA) have been studied by using different techniques including circular and linear dichroism (CD and LD, respectively) and UV-visible absorbance spectroscopies, gel electrophoresis, fluorescence competitive-binding studies and atomic force microscopy (AFM). ...
... Keywords: atomic force microscopy · binding studies · DNA · metallacalixarenes · platinum anionic substrates. [5][6][7] In particular, we have observed that metallacalixarenes are especially suited for supramolecular interactions with mononucleotides [8] with some examples of enantioselective recognition processes. [9] These previous results have prompted us to investigate the possible use of metallacalixarenes as selective DNA binding agents. ...
... [10] The most remarkable feature of the 1 H NMR spectra is that the H4,H4' resonances are shifted downfield on passing from the chloro-substituted pymo derivative (d = 8.43 ppm), to the bromo (d = 8.49 ppm) and iodo (d = 8.53 ppm) derivatives, as expected. The 1 H NMR spectra also show that the compounds do not decompose in aqueous solution even during long storage periods and over a wide range of pH (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13), which is in agreement with the highly inert nature of the Pt À N bonds. Variable-temperature 1 H NMR experiments (22-85 8C) have been performed for species 1, 2, 3 and 4 to explore their conformational flexibility. ...
Metallacalixarenes were bound to DNA in a supramolecular fashion to induce a series of unprecedented sequential conformational changes. Clear noncovalent interactions between platinum-containing metallacalix[4]arenes and calf thymus DNA are described by M. J. Hannon, A. Rodger, F. Zamora, J. A. R. Navarro et al. in their Full Paper on page 5075 ff. These interactions were expected, and were deduced from spectroscopic and atomic force microscopy studies.
... Substituted-pyrimidinic ligands have been demonstrated to be excellent and versatile building blocks with charge and multiconnectivity ability to produce, under conventional and hydrothermal conditions, multidimensional coordination polymers with interesting properties [1][2][3][4][5]. Recently, we have shown that it is possible to synthesise new coordination compounds, with fascinating structures and interesting physical properties, by combining transition metal ions with the 1,2,4-triazolo [1,5-a] pyrimidine ligand (tp) and several pseudohalide auxiliary spacers [6]. ...
... In this paper, we report the antiparasital properties of the following three new metal complexes: (a) the mononuclear unit [Cu(HmtpO) 2 (3). We have studied the antiproliferative in vitro and in vivo activity of these complexes against T. cruzi (epimastigote, amastigote and trypomastigote forms). ...
... Transition element ions (TEI) have a good and important role in the self-assembly of complexes. Additionally, the wide field of chemistry using transition elements and organic ligands as building blocks is enriched with high design ability and a variety of structural architecture [1][2][3][4]. The cobalt(II), copper(II), and zinc(II) ions are of particular interest because they relate to labile metal centers with the coordination number of M 2+ ranging from two to six and more. ...
In the present work, complexes of cobalt(II), copper(II), and zinc(II), 2-amino-4-methylpyrimidineand, and 2,3-diaminopyridine were successfully prepared and characterized using elemental analysis, UV-visible, and FTIR spectroscopy, as well as magnetic susceptibility measurements, molar conductance, TGA analysis, and X-ray diffraction. From elemental and spectral data, the formulae [M(L1)(L2)Cl2(H2O)] (where L1 = AMPY (2-amino-4-methylpyrimidine) and L2 = DAPY(2,3-diaminopyridine)) and M = Co(II) (2), Cu(II) (2), and Zn(II)) for the metal complexes have been proposed. The geometric structures of the mixed-ligand complexes were found to be octahedral around the metal ions, and the XRD patterns showed monoclinic crystal systems with space group P21. The mode of bonding was pentacoordinate for Cu and hexacoordinate for Zn and Co. Different features may result from the fact that not all molecules have the same electron distribution. For example, Zn and Co have larger electron densities in at least one of the chlorides in the HOMO compared with pentacoordinate Cu, which has a small electron distribution on the chloride. Thermal analysis indicated that all metal complexes are stable up to about 88 °C with thermodynamically favored overlapped chemical reactions. Excellent antibacterial and antifungal activity was shown by the three synthesized forms of the complexes. The Zn(II) complex had a high level of antioxidant activity with a DPPH scavenging of 91.5%, whereas the Cu(II) complex had a low level of antioxidant potential (16.5%). The docking tests also showed that all compounds had good binding energy levels (7.2–7.9 kcal mol−1). For this reason, all molecules can easily fit in the receptor protein’s catalytic sites. However, the Co(II) complex is shown to be more active.
... Transition element ions (TEI) have a good and important role in the self-assembly of complexes. Additionally, the wide field of chemistry using transition elements and organic ligands as building blocks is enriched with high design ability and a variety of structural architecture [1][2][3][4]. The cobalt(II), copper(II), and zinc(II) ions are of particular interest because they relate to labile metal centers with the coordination number of M 2+ ranging from two to six and more. ...
[Co(AMPY)(DAPY)Cl2(H2O)].H2O (1) [Cu(AMPY)(DAPY)Cl2(H2O)].H2O (2) [Zn(AMPY)(DAPY)Cl2(H2O)] (3) were prepared from the ligands; AMPY = 2-amino-4-methylpyrimidine (L1), DAPY = 2,3-diaminopyridine (L2) and CoCl2.6H2O, CuCl2.2H2O and ZnCl2 in water/ethanol solutions and the three products characterized by elemental analysis, ultraviolet-visible spectroscopy (UV–Vis), Fourier-transform infrared spectroscopy (FT-IR), magnetic susceptibility, molar conductivity methods, and TGA analysis. The X-ray powder diffraction of the Co(II), Cu(II), and Zn(II) compounds showed that the geometry of monoclinic and SEM analysis revealed their morphology with a smooth surface. Molecular modeling was performed for all compounds using the density functional method DFT/B3LYP to study the structures and the frontier molecular orbitals (HOMO and LUMO). We have used Gaussian09 software for the calculations. In this study, different complexes were tested against Gram negative and Gram positive bacterial species to give insight into their broad-spectrum effects. The used pathogenic strains were two Gram positive species "Staphylococcus aureus and Micrococcus luteus" and two Gram negative species "Salmonella thyphimurium and Escherichia coli. The antifungal activity was evaluated against a pathogenic reference strain of the yeast Candida albicans. The antimicrobial and antioxidant assay results demonstrate that the tested compounds are effective against Gram positive and negative bacteria. Additionally, the compounds have an antifungal effect against Candida albicans with a maximum inhibitory zone of 2.5cm. The results demonstrated high antioxidant potential for the Zn(II) complex with a DPPH scavenging of 91.5%, however, the Cu(II) complex was low (16.5%). The data of docking with tyrosyl-tRNA synthetase presented that all compounds fit very well in the catalytic pockets of the proteins of the receptor.
... In addition to their ubiquity in the biological sciences, pyrimidine derivatives are also common building blocks in many functional materials such as supramolecular assemblies, non-linear optics and organic electronics. [2] The ring C-H metalation of pyrimidines offers a direct means to further functionalize these systems, [3] and this has been successfully implemented at C2, [4] C4, [5] and C5. [6] However, ring metalation requires strong bases and often leads to low yields of products due to the propensity of these intermediates to undergo dimerization. ...
We report a novel and general method to access a highly under‐studied privileged scaffold—pyrimidines bearing a trifluoroborate at C4, and highlight the broad utility of these intermediates in a rich array of downstream functionalization reactions. This chemistry is underpinned by the unique features of the trifluoroborate group; its robustness provides an opportunity to carry out chemoselective reactions at other positions on the pyrimidine while providing a pathway for elaboration at the C−B bond when suitably activated.
... In addition to their ubiquity in the biological sciences, pyrimidine derivatives are also common building blocks in many functional materials such as supramolecular assemblies, non-linear optics and organic electronics. [2] The ring C-H metalation of pyrimidines offers a direct means to further functionalize these systems, [3] and this has been successfully implemented at C2, [4] C4, [5] and C5. [6] However, ring metalation requires strong bases and often leads to low yields of products due to the propensity of these intermediates to undergo dimerization. ...
Stable and enabling: Pyrimidine trifluoroborates are an under‐developed scaffold that have been rarely reported in the literature. These compounds participate in a rich array of downstream functionalization reactions that are underpinned by the unique features of the trifluoroborate group; its robustness provides an opportunity to carry out chemoselective reactions at other positions on the pyrimidine while providing a pathway for elaboration at the C−B bond when activated.
Abstract
We report a novel and general method to access a highly under‐studied privileged scaffold—pyrimidines bearing a trifluoroborate at C4, and highlight the broad utility of these intermediates in a rich array of downstream functionalization reactions. This chemistry is underpinned by the unique features of the trifluoroborate group; its robustness provides an opportunity to carry out chemoselective reactions at other positions on the pyrimidine while providing a pathway for elaboration at the C−B bond when suitably activated.
... Among neutral ligands, pyrazines are especially useful as pillars in the construction of pillared-layer in 2D/3D network and pyrazine is a well-known bridging ligand that has been used in the preparation of MOFs [20,21]. Pyrazines have nitrogen lone electron pairs that are highly directional and have attracted much attention in the construction of supramolecular structures such as porous materials [22,23] and molecular grids [24,25]. Herein, we report on the unanticipated reaction of pyrazine with copper(II) nitrate to form a copper(I) metal-organic framework. ...
A new copper(I) pyrazine-bridged coordination polymer [Cu2(pyz)3(NO3)2]·2DMF] (pyz = pyrazine) (1) has been synthesized and characterized by FT-IR, TG/DTG, DSC and single crystal X-ray diffraction techniques. The X-ray crystallographic result reveals a two-dimensional network structure containing hexagonal pores. Thermal analysis of compound 1 reveals it is stable to 380 °C, and gas sorption studies showed that it adsorbs 1.04 wt% hydrogen at 1 atm and 77 K. Compound 1 crystallizes in a triclinic system, space group P-1 (no. 2), a = 7.9550(2) Å, b = 7.9810(2) Å, c = 11.0660(3) Å, α = 76.328(1)°, β = 71.115(1)°, γ = 84.577(1)°, V = 645.79(3) Å3, Z = 2, T = 150(2) K, μ(MoKα) = 1.709 mm-1, Dcalc = 1.639 g/cm3, 11111 reflections measured (7° ≤ 2Θ ≤ 54.96°), 2951 unique (Rint = 0.0539) which were used in all calculations. The final R1 was 0.0346 (>2σ(I)) and wR2 was 0.0727 (all data).
... 12 Similarly, discrete metallosupramolecular hexagons based on pyrimidines (e.g. pyrimidine, 2-hydroxypyrimidine, 2,4-dihydroxypyrimidine, 2-aminopyrimdines) have been reported by Navarro et al. 13 Inspired by the aforementioned discrete assemblies, we opted to use an in-house synthesized pyrimidine-based ligand (H2-4,5pmbc: 4-(pyrimidyl-5-yl)benzoic acid) and explore its potential in directing the assembly of extended frameworks based on hexagonal supramolecular building units. The 4,5-pmbc is a multifunctional ligand encompassing one carboxylate group and two aromatic N-donors centers, offering several coordination modes as depicted in Scheme 1. ...
Three novel metal-organic frameworks (MOFs) were isolated upon reacting a heterofunctional ligand 4 (pyrimidin-5 yl)benzoic acid (4,5-pmbc) with mixed valence Cu(I,II) under solvothermal conditions. X-ray crystal structural analysis reveals that the first compound is a layered structure composed of one type of inorganic building block, dinuclear paddlewheel [Cu2(O2C–)4], which are linked through 4,5-pmbc ligands. The two other supramolecular isomers are composed of the same Cu(II) dinuclear paddlewheel and a dinuclear Cu2I2 cluster, which are linked via the 4,5-pmbc linkers to yield two different 3-periodic frameworks with underlying topologies related to lvt and nbo. The observed structural diversity in these structures is due to the distinct coordination modes of the two coordinating moieties (the carboxylate group on the phenyl ring and the N-donor atoms from the pyrimidine moiety).
... A partial summary of our studies can be found in Refs. [10][11][12]. Worthy of note, among the many species prepared during this ongoing project, interesting functional materials could be prepared: molecular magnets [13]; second harmonics generation-active polymers [14]; nanoporous MOFs with high gas storage capacity and size-selective catalytic activity [15]. ...
Several alkyl- or aryl-tin(IV) halides of general formula SnRnX4−n (n=0–2; R=Me, Et, nBu, tBu, Ph; X=Cl, Br), possessing Lewis acidic character, have been reacted with the polydentate N-donor ligand bis(1,2,4-triazolyl)methane (Btm), affording Btm(SnRnCl4−n) complexes. (Btm)2SnnBu2Br2 and (Btm)SnnBu2(NO3)2 are also reported. These materials were characterized by elemental analyses, IR and 1H (and, in selected cases, 119Sn) NMR spectroscopy, and, were possible, ab initio X-ray powder diffraction methods. The crystal structures determined by the latter method showed that Btm ligands, in the exobidentate mode, link Sn(IV) fragments which lie 9.5–11.2Å apart (depending on the Btm conformation and on the local metal stereochemistry), in one-dimensional chains packed in parallel bundles. The main geometrical features of these 1D polymers are compared with those of the bis(imidazolyl)methane complexes and of the known Btm derivative, Btm(Ph2SnBr2). Interestingly, the expected isomorphous structures for selected couples was not found, as if very subtle energetic differences were driving the crystallization of these species into different structure types.
... With pyrimidine itself (and a tetrahedral ZnI 2 entity) [12] or with 4-hydroxypyrimidine (and cis-squareplanar Pd II ) [13] cycles with n = 3 are known, but larger ring sizes are more common with differently substituted pyrimidine rings. [14] The purine model nucleobases 9-methylhypoxanthine (9-MeHxH) and 9-ethylhypoxanthine (9-EtHxH) were pre- pared as reported, [15] and the X-ray crystal structure of 9-EtHxH was determined (see the Supporting Information). Reactions of 1 a and 1 b with (en)Pd II were carried out initially on an NMR scale, with relative ratios r and pD varied. ...
Vase-shaped hexanuclear (Pt3Pd3) complexes with 9-alkylhypoxanthinate ligands bridging three (en)PdII units through N1 and N3 sites are reported, which bind ClO4− ions in their cavities, albeit not in strictly analogous ways. The structural differences reflect the flexibility of the host cation and may even be relevant to the mechanism of ClO4− incorporation into the host or ejection from it.
... The dicarboxylates, as important organic anions, have attracted intense interest from chemists due to its versatile coordination modes in the assembly of polymeric structures [15][16][17][18][19][20][21][22]. So far, although dicarboxylates are widely utilized in the construction of coordination polymers [6,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], metal-organic frameworks (especially for central metal silver) built by dicarboxylates and heterocyclic pyrimidine and its derivatives, are relatively rare [31,32]. ...
通讯作者地址: Huang, RB (通讯作者), Xiamen Univ, Dept Chem, Coll Chem & Chem Engn, Xiamen 361005, Peoples R China 地址: 1. Xiamen Univ, Dept Chem, Coll Chem & Chem Engn, Xiamen 361005, Peoples R China 2. Xiamen Univ, State Key Lab Phys Chem Solid Surfaces, Xiamen 361005, Peoples R China 电子邮件地址: rbhuang@xmu.edu.cn Using the principle of crystal engineering, three new silver metal–organic coordination polymers, [Ag2(L1)2(L2)]·2H2O (1), [Ag2(L1)2(L3)]·H2O (2), [Ag2(L1)2(L4)]·2H2O (3) (L1 = 2-aminopyrimidine, L2 = oxalate anion, L3 = glutarate anion and L4 = 1,4-naphthalenedicarboxylate anion) have been synthesized by solution phase reactions of silver nitrate with various dicarboxylic acids and cooperative heterocyclic 2-aminopyrimidine ligand under the ammoniacal conditions. All the complexes have been characterized by elemental analyses, IR spectra and X-ray diffraction. In complex 1, L1 ligands are coordinated to Ag(I) metal centers in rare tridentate fashions, forming one-dimensional (1-D) ladder-like structure, which is interlinked by L2 anions to generate 2-D pleated molecular sheet. Complex 2 displays an interesting two-dimensional (2-D) tongue-and-groove structure containing a new kind of “T-shaped” unit. Meanwhile, each of 2-D bilayers is interlocked by four adjacent identical motifs to form three-dimensional (3-D) 5-fold interpenetrating conformation with weak Ag···Ag interactions. In complex 3, L1 ligands are coordinated to the Ag(I) ions to form 1-D polymeric chain. And L4 anions, acting as bridging linkers through corresponding μ2-carboxylates, link a pair of Ag(I) atoms from adjacent chains to yield 3-D supramolecular network. The structures of complexes 1–3 which span from 2-D to 3-D networks suggest that dicarboxylate anions play important role in the formation of such coordination architectures. National Natural Science Foundation of China 20721001 973 Project, MSTC 2007CB815301
In this review we report on the enantiomerization of tetrahedral racemic‐[(NH4)4∩{Mg4(L¹)6}] monitored by means of variable temperature (VT) ¹H NMR spectroscopy. The enantiotopization of the diastereotopic protons is due to simultaneous Bailar twists at the four octahedrally coordinated magnesium centres, synchronized with atropisomerization of the six edge‐bridging ligands (L¹)2‐.The VT ¹H NMR spectrum of tetrahedral meso‐[In4(L²)4] is coined through the helicity of the four face‐centred tripodal hexadentate ligands (L²)3‐ and can, alike the ¹H NMR of cyclic meso‐[In6Cl6(L³)6], be explained by the enantiotopization of the diastereotopic protons via mesomerization.
Nucleobases, the constituents of nucleic acids, represent excellent building blocks for supramolecular constructs because they combine several essential properties responsible for the generation of supramolecules, namely, the abilities for hydrogen bond formation, for π–π stacking, and for metal coordination. Biologically relevant in several instances, these features allow for mutual molecular recognition, binding of anions and cations, as well as pH-dependent movements of entities, among others. At the same time, artificial analogues of naturally occurring supramolecular features in nucleic acids can be synthesized which are based on principles well established in coordination chemistry. This chapter reviews mainly work involving heavier transition metal ions, in particular, but not exclusively, PtII and PdII.
As is well established, numerous similarities exist as far as reactivity patterns and structural features of the d⁸ metal ions M = Pd²⁺ and Pt²⁺ are concerned. Here reactions of metal complexes of type cis-[M(a)2X2] (a = NH3 or (a)2 = diamine or diimine; X = monodentate or X2 = bidentate leaving groups) with nucleobases, the constituents of nucleic acids, are discussed and differences regarding intrinsic stability of the starting compounds, kinetics of formation of products, thermodynamics of products, as well as donor site selectivity are pointed out. It is concluded that PdII complexes representing strict or close analogues of established antitumor PtII drugs of the Cisplatin-type, if active under in-vivo conditions at all, are unlikely to have a similar mode of action as their PtII congeners. Relationships to supramolecular constructs containing cis-[M(a)2]²⁺ entities are likewise discussed.
Structural analyses of a flexible 1D MOF [Cu(BF4)2(bpp)2] (bpp = 1,3-bis(4-pyridyl)propane) with/without guest molecules were performed by synchrotron powder X-ray diffraction analysis and single crystal structural analysis. The guest-free MOF is composed of 1D chains composed of Cu(II) ions and bpp ligands which are accumulated to form quasi-2D layers, resulting in a quasi-layered compound. The guest-free MOF has no open pore windows; it, however, has latent quasi-hexagonal cavities surrounded by six BF4 anions. This MOF shows molecular selective sorption, which stems from guest-dependent dynamic structural transformation including pore-opening/closing processes. It shows selective alcohol sorption based on the molecular recognition properties; it sorbs C1-C3 alcohols, but not a C4 alcohol (1-butanol). Sorption properties can be enhanced by accumulation of several functionalities. In the case of the flexible MOF, the sorption properties should be synergetically enhanced by several key properties; it has molecular recognition properties and accommodate selected species with pore-opening, and furthermore prevent other species entering cavities by pore-closing.
Octanuclear [Ni2(L)(H2O)2]4·7CH3OH·12H2O (1·7CH3OH·12H2O) and tetranuclear [Cu2(HL)(CH3OH)1.5(H2O)1.5]2(ClO4)2·2CH3OH (2·2CH3OH) (H4L = 4-carboxysalpn or N,N′-bis(4-carboxysalicylidene)-1,3-propylenediamine) are obtained from similar reactions, the main difference coming from the slightly higher pH of the medium for the nickel reaction vessel. This small disparity of the pH leads to full deprotonation of the ligand in 1 while one of the carboxylic functions remains protonated in 2, making it unable to act as a donor and, therefore, justifying the different nuclearity of both compounds. In any case, the isolation of complexes of H4L with limited nuclearity is remarkable, given that similar carboxysalen-based ligands lead to coordination polymers when the carboxylic functions are partially or fully deprotonated. This indicates that not only the pH of the medium but also the longer propylene spacer of the Schiff base have a fundamental role in the nuclearity of the isolated products. 1·7CH3OH·12H2O is an odd Ni8 1,3-alternate metallacalix[4]arene, formed from four symmetry-related [Ni2(L)(H2O)2] metalloligands, joined through the fully deprotonated carboxylic functions. 2·2CH3OH is a molecular rhomboid, built from two [Cu2(HL)(CH3OH)1.5(H2O)1.5]+ metallotectons, linked through the only deprotonated carboxylic group of the ligand, the protonated carboxylic moiety remaining uncoordinated. In addition, the magnetic analysis of both polynuclear compounds shows that they are antiferromagnetic in nature and that the magnetic interaction between dinuclear metallotectons is negligible.
The design of multinuclear metal complexes requires a match of the ligand-to-metal vectors and the preferred coordination geometries of the metal ions. Only a few ligands are known with a parallel orientation of N→M vectors that brings the metal ions into close proximity. We establish here the adenine derivative 1,N(6)-ethenoadenine (εA) as an ideal bis(monodentate) ligand. Scanning tunneling microscope images of alkylated εA on graphite surface clearly indicate that these ligands bind to Ag(I) ions. The molecular structures of [Ag2(1)2](ClO4)2 and [Ag2(2)2](ClO4)2 (1, 9-ethyl-1,N(6)-ethenoadenine; 2, 9-propyl-1,N(6)-propylenoadenine) confirm that dinuclear complexes with short Ag···Ag distances are formed (3.0256(3) and 2.984(1) Å, respectively). The structural motif can be extended to divalent metal ions, as was shown by determining the molecular structure of [Cu2(1)2(CHO2)2(OH2)2](NO3)2·2H2O with a Cu···Cu distance of 3.162(2) Å. Moreover, when introducing the 1,N(6)-ethenoadenine deoxyribonucleoside into parallel-stranded DNA duplexes, even dinuclear Ag(I)-mediated base pairs are formed, featuring the same transoid orientation of the glycosidic bonds as the model complexes. Hence, 1,N(6)-ethenoadenine and its derivatives are ideally suited as bis(monodentate) ligands with a parallel alignment of the N→M vectors for the construction of supramolecular metal complexes that require two metal ions at close distance.
Hypocrellin B (HB) can chelate with Mg2+ and Zn2+ ions to form the coordination complexes Mg2+-HB and Zn2+-HB, which consist of 5-22 repeat units. The structures of these two complexes are characterized by ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and 1H nuclear magnetic resonance (H-1 NMR). The relative quantum yields of singlet oxygen (O-1(2)) for Mg2+-HB and Zn2+-HB are 1.2 and 0.42 times as high as that of HB, respectively. Transient absorption spectra results indicate that O2 is able to quench the triplet excited state of Mg2+-HB and Zn2+-HB with an efficiency higher than 96%. The intersystem crossing efficiency (phi(T)) and the fraction of triplet states quenched by O-2 that yield O-1(2) (f(Delta)(T)) are considered to be essential for the singlet oxygen quantum yields of HB and its complexes. Electron paramagnetic resonance (EPR) results suggest that Mg2+-HB and Zn2+-HB have a weak ability to generate a semiquinone anion radical, which reduces the generation of the superoxide anion radical (O-center dot(2-)) by Mg2+-HB and Zn2+-HB. The results of the UV-Vis spectra and the deoxyribonucleic acid (DNA) melting temperature experiments indicate that Mg2+-HB and Zn2+-HB bind with calf thymus (CT) DNA in an electrostatic interaction mode. Under aerobic conditions, the efficiencies of photoinduced damage to CT DNA by Mg2+-HB, HB, and Zn2+-HB are found to be 32%, 25%, and 22%, respectively. The reactive oxygen quencher experiments indicate that singlet oxygen is the main component generated by Mg2+-HB that damages CT DNA.
Soft porous coordination polymers (soft PCPs) are a unique class of porous crystalline materials that combine pore regularity of crystalline porous materials with transformability of enzymes. The combination of both features is highly advantageous since flexibility facilitates guest exchange and selective chemical reactions within the pores without the loss of structural integrity. Crystallinity confers regularity to the porous structure with structure response in a cooperative way to physical or chemical stimuli. The soft nature of these materials may arise from the plasticity of the coordination polyhedron, the flexibility of the organic bridging ligands, the presence of weak interactions (H-bonding, Π-Π staking, electrostatic and van der Waals interactions), or a combination thereof. Thus, this type of crystalline materials exhibit reversible transformability between states (bistable or multistable) with long-range structural ordering and permanent porosity. This type of materials are sensitive to external physical and chemical stimuli. As a consequence, soft PCPs have unique properties, which are highly valuable for applications in the fields of separation processes, drug delivery, electrical and ion conduction, sensing, switches, energy storage and conversion, and selective heterogeneous catalysis.
Coordination compound [CdI2(Ampym)2] is synthesized by the reaction of 2-amino-4-methylpyrimidine (Ampym, C5H7N3) with CdI2 in an acetonitrile–ethanol (20 : 1) mixture, and its crystal structure is determined. The crystals are triclinic, space group P
\(\overline 1 \), a = 6.241(1), b = 11.929(1), c = 12.259(1) Å, α = 81.78(1)°, β = 78.82(1)°, γ = 75.82(1)°, V = 863.6(2) Å3, ρcalcd = 2.248 g/cm3, Z = 2. The cadmium atom has a tetrahedral coordination by two nitrogen atoms of crystallographically nonequivalent ligands L and two iodine atoms (Cd(1)–Nav 2.305(6), Cd(1)–I(1) 2.7093(8), and Cd(1)–I(2) 2.7235(7) Å). The angles at the Cd atom are 100.8(2)°–124.51(3)° (the maximum value corresponds to the ICdI angle). The planar rings N2C4 (±0.01 Å) of coordinated ligands L are arranged at an angle of 84.8° relatively to each other. The complexes are joined by hydrogen bonds N–H⋯N into zigzag supramolecular chains.
The coordination compounds [CoL2Cl2] (I) and [CdL2(H2O)(2)(NO3)(2)] (II) have been synthesized by the reaction of CoCl2 center dot 6H(2)O and Cd(NO3)(2) center dot 4H(2)O with L = 2-amino-4-methylpyrimidine (Ampym, C5H7N3), and their structures have been solved. The crystals of complex I are triclinic, space group , a = 5.627(1) , b = 11.191(1) , c = 12.445(1) , alpha = 81.00(1)A degrees, beta = 77.21(1)A degrees, gamma = 76.18(1)A degrees, V = 737.7(2) (3), rho(calcd) = 1.567 g/cm(3), Z = 2. The crystals of complex II are monoclinic, space group P2(1)/c, a = 10.390(1) , b = 11.982(1) , c = 7.624(1) , beta = 102.61(1)A degrees, V = 926.1(2) (3), rho(calcd) = 1.760 g/cm(3), Z = 2. Discrete [CoL2Cl2] moieties are realized in the structure of complex I. The cobalt atom is tetrahedrally coordinated to the two nitrogen atoms of crystallographically nonequivalent ligands L and two chlorine atoms (Co(1)-N-avg, 2.051(4); Co(1)-Cl(1), 2.241(1) ; Co(1)-Cl(2), 2.263 ; bond angles at the cobalt atom lie within a range of 102.1A degrees-118.6A degrees). The complexes are linked into supramolecular zigzag chains by N-H...N(Cl) hydrogen bonds. In the structure of complex II, the Cd2+ ion (at the inversion center) is coordinated in pairs to the nitrogen atoms of ligand L and the O(NO3) and O(H2O) oxygen atoms. The coordination of the Cd2+ ion is distorted octahedral (Cd(1)-N(1), 2.341; Cd(1)-O(1), 2.340(4) ; Cd(1)-O(4), 2.327(3) ; bond angles at the cadmium atom lie within a range of 79.1A degrees-100.9A degrees). N-H...N hydrogen bonds link the complexes into supramolecular chains. These chains are linked into a supramolecular framework by the O-H...O hydrogen bonds between water molecules and NO3 groups.
The palladium-catalyzed carbonylation of iodoferrocene was investigated in the presence of 2-aminopyrimidine derivatives as nucleophiles. 2-Amino-4-hydroxy-6-methylpyrimidine was found to act both as an O- and an N-nucleophile, leading to an ester and an amide derivative, respectively. Together with other spectroscopic methods, the structure of both products was proved by X-ray crystallography. 2-(Ferrocenoylamino)-4-chloro-6-alkylpyrimidines were obtained during carbonylation of iodoferrocene and 2-amino-4-chloro-6-alkylpyrimidines. The formation of a dimeric product via two subsequent carbonylation steps was also observed. The products may have practical importance as electrochemically detectable biosensors or building blocks for supramolecular assemblies.
Reactions of AgReO4 and AgCH3SO3 with L = 2-amino-4-methylpyrimidine (Ampym, C5H7N3) in a ratio of 1: 2 in acetonitrile gave the complexes [AgL2(ReO4)] (I) and [AgL2(CH3SO3)] (II). Their structures were determined. The crystals of complex I are monoclinic, space group C2/c, a = 5.985(1), b = 3.465(1), c = 19.071(1) Å, β = 96.52(1)°, V = 1527.0(3) Å3, ρcalcd = 2.507 g/cm3, Z = 4. The crystals of complex II are orthorhombic, space group Pbca, a = 14.784(1), b = 11.991(1), c = 17.711(1) Å, V = 3139.7(4) Å3, ρcalcd= 1.782 g/cm3, Z = 8. Structure I shows discrete cationic complexes [AgL2]+. The silver atom is virtually linearly coordinated to two N atoms of crystallographically equivalent ligands L (Ag-N, 2.156(4) Å; the angle NAgN, 174.7(4)°). The complex cations are united into zigzag chains through the hydrogen bonds N-H...N. The resulting chains are linked by the hydrogen bonds N-H...O to uncoordinated perrhenate anions to form 2D supramolecular layers. In structure II, the Ag+ ion is coordinated by two crystallographically non-equivalent ligands L in a distorted linear fashion: Ag(1)-N(1), 2.166(7) Å;Ag(1)-N(4), 2.181(6) Å; the angle NAgN, 157.2(2)°. The anions CH3SO3 − are weakly linked to the Ag+ ions (Ag...O 2.72 Å) and are hydrogen-bonded to the complex cations [AgL2]+, uniting them into supramolecular ribbons.
Metallacalix[n]arenes are a distinct class of metallacyclic compounds consisting of heteroaromatic rings L and square-planar cis-a2MII entities (M = Pt or Pd; a = NH3 or amine; or a2 = chelating diamine) instead of methylene bridges as in the classic calix[n]arenes. Here a series of hybrid compounds is described, which simultaneously have bridging –CH2– as well as cis-a2MII units, and uracil containing ligands L. Specifically, L = bis(1-methyluracil-5-yl)methane (1) and in one case a derivative of it, bis(1-methyluracil-5-yl)methylbenzene (2), have been reacted with cis-[a2M(H2O)2]2+ (with a = NH3 or a2=2,2’-bipyridine or bis(pyrazloyl-1-yl)propane) in water and products were isolated. Altogether X-ray crystal structures of eight metallacycles (complexes 3–6, 8–11) of M2L2, M4L2, and M6L6 stoichiometries have been determined as well as a second modification of 1. In all closed metallacycles the 1-methyluracil entities are deprotonated with metals coordinating via N3 positions, and without exception the uracil rings adopt 1,3-alternate conformations. A special feature of ligand 1 in its twofold deprotonated form is its propensity to bind additional metal ions through its exocyclic oxygen functionalities. While O4 sites appear to be favored as secondary metal binding sites, linkage isomerism and involvement of O2 is likewise possible (compounds 4, 9, 10). On the basis of the X-ray crystal structures, a reaction scheme is proposed which accounts for the different stoichiometries observed.
Two new coordination compounds [Ag6(NHdmpym)2(dppm)4] (1·4ClO4) and [Ag4(NHpym)2(dppm)2] (2·2ClO4·2DMF) (NH2dmpym = 2-amino-4, 6-dimethylpyrimidine, NH2pym = 2-aminopyrimidine, dppm = bis(diphenylphosphino)methane, DMF = N, N-dimethylformamide) have been synthesized under the ammoniacal conditions and structurally characterized. In 1 and 2, NH2dmpym and NH2pym ligands are deprotonated and show rare μ4-N1:N1:N2 and μ3-N1:N2 coordination modes, respectively. The bridging dppm ligand combines the N-donor ligands to give 1 and 2 triangle Ag3 and rectangle Ag4 cores, respectively. The resulting Ag3 metallacycle is a scalene triangle with an average Ag···Ag distance of 3.1043(9) Å. The Ag4 metallacycle is an irregular rectangle with a shorter and a longer Ag···Ag distances of 2.8852(15) and 3.3202(13) Å, respectively. The structural variances between 1 and 2 are caused by the ratios of metal and ligands and substituent group effect. In addition, 1 and 2 exhibit blue photoluminescence which may be assigned to ligand-to-metal charge transfer (LMCT) transition.
We synthesized pyrimidine-4,6-diyl bis(tert-butyl nitroxide) (pmbNO), and characterized as a biradical by means of ESR spectroscopy. The zero-field splitting parameters were |D|/hc = 2.52 × 10−2 cm−1 and |E|/hc = 2.34 × 10−3 cm−1 in frozen toluene at 100 K. Magnetic study clarified the presence of intramolecular ferromagnetic coupling with 2J/kB = +18.5(5) K in frozen toluene–ethanol. DFT calculation supports the ground triplet state of pmbNO. The reaction of pmbNO with Cu(hfac)2 gave [Cu3(pmbNO)2(hfac)4], and the structure was determined by X-ray crystallographic analysis. Though the ligand was reduced to be an anion radical, pmbNO is confirmed to work as a rigid bridge, and the nitroxide oxygen atoms can ligate the metal ions.
Under hydrothermal conditions, a novel five-connected three-dimensional metal-organic coordination polymer [Cd(mpdc)] is self-assembled from 2,6-dimethylpyridine-3,5-dicarboxylate (mpdc), by taking advantage of simple modifications of pyridyldicarboxylates, and cadmium ions. The X-ray single diffraction reveals that the [Cd(mpdc)] with M5L5 mode exhibits zeolite-like framework with interesting helical chains in diamondoid net of CdII. In addition, the compound with high thermal stability up to the temperature of 430 °C exhibits strong photoluminescent at room temperature in the solid state.
The use of 4-cyanopyridine (4-CNpy) and 3-cyanopyridine (3-CNpy) as ditopic ligands with 180° and 120° directionalities, respectively, for the construction of molecular architectures with the 90° metal fragments (en)PtII and (en)PdII in water is hampered by the ease with which these ligands undergo hydrolysis to isonicotinamide (4-C(O)NH2py) and nicotinamide (3-C(O)NH2py). As described in this article, out of six X-ray structurally characterized complexes (1–6), only a single one (1) reveal coordination of the unchanged ligand (4-CNpy) to (en)PtII. Nevertheless also the hydrolysis products are of interest in the context of obtaining discrete metallacyclic compounds: Thus, (en)PtII and 4-C(O)NH2py form a hexanuclear complex, [PF6⊂⊂{(en)Pt}6(4-C(O)NHpy)4](NO3)7·10H2O (2), in which the anionic isonicotinamidate ligands function as tridentate, bridging ligands to produce a hybrid between a metallasquare and a 2-floor open box. The resulting cation with a +8 charge accommodates a single hexafluorophosphate anion in its interior. Adjacent cations of 2 pack in such a way as to develop Pt4 chains as typically seen in “platinum blues” and their [PtII]4 precursors.
In this contribution, we discuss the use of simple pyrimidine derivatives and geometrically related heterocycles in combination with protected metal ions to build cyclic polynuclear coordination assemblies. The resulting assemblies range from conformationally rigid triangles to corrugated octagons with positively charged cavities and surfaces that can interact with anionic species in a supramolecular fashion. Special attention has been focussed to the supramolecular interaction of these systems towards mononucleotides and DNA as a possible novel interaction of DNA binding metallo-drugs. The results show that these systems efficiently interact with both mononucleotides and ds-DNA. The molecular recognition of ds-DNA leads to significant conformational changes, however, this interaction gives only rise to moderate cytotoxic effects towards tumour cell lines.
This chapter reviews that the account of an infant discipline of metallacalixarenes, the metallo-version of heterocalixarenes and a unique category of organo-inorganic hybrid systems elaborates many of their distinctive features with respect to other synthetic receptors. Their metallic components are primarily responsible for the multifold positive charge of the species that visibly constitute attractive hosts for anions so significant in biological reactions. The intrinsic magneto-electrical and structural contribution of metals could impart in metallacalixarenes such unusual features in target functional materials. An abundant use of nucleobases in their designs and large non-existent in parent heterocalixarenes, points to their relevance in mimicking supramolecular phenomenon in biological systems. Only four model heterocycles have so far been used in evolving metallacalixarenes, points to the lack of awareness amongst practitioners of heterocyclic chemistry. It is hoped that their involvement in the exploration of this interfacial area will prove increasingly fruitful.
Transcending consideration of covalent versus non-covalent bonding, supramolecular chemistry considers building blocks instilled with angles, coordination sites, and affinities that drive their assembly to architectures with utilities and designs not accessed from the starting materials alone. This chapter discusses new developments in heterocyclic chemistry pertaining to hexameric macrocyclic architectures, highlighting salient synthetic features of ring construction whereby the participating heterocyclic building blocks, or subunits, possess at least one heteroatom, such as nitrogen, oxygen, or sulfur. The chapter also focuses on macrocycles with five-membered heterocyclic subunits, six-membered ring heterocycles, and some miscellaneous heterocyclic materials. The chapter emphasizes that the use of heterocyclic species, such as furan, pyrrole, thiophene, and pyridine, for the preparation of stable, hexameric (macro) molecular architectures has been demonstrated as a logical pathway to functional materials. This is based, in part, on the mature chemistry and ready availability of these versatile building blocks. Step-wise procedures and self-assembly protocols combined with ingenuity and creativity have led to the crafting of architecturally controlled species such as Stang's metal-directed metallocycles, Schlu¨ ter's bipyridine phenylacetylenes, Lehn's self-assembling helicates, and Newkome's bisterpyridine-based constructs.
Adsorption isotherms of N2, O2, CO2, and Xe on a flexible microporous coordination polymer, CPL-2 [Cu2(pzdc)2(bpy)]·(pzdc=pyrazine-2,3-dicarboxylate; bpy=4,4′-bipyridine), possessing bellows-shaped one-dimensional channels were measured. A nonintegral number of each of the N2, O2, CO2, and Xe molecules can be accommodated in each unit pore, which indicates that all guest molecules are accommodated in the so-called “incommensurate fashion”. In situ synchrotron X-ray powder diffraction patterns of CPL-2 with guest molecules were recorded. The unit cells were determined from each pattern. It was found that the host CPL-2 exhibits different crystal transformation with the accommodation of each guest molecule. This indicates that, even in the case of incommensurate adsorption, the flexible framework of a microporous coordination polymer can transform each pore to suit different guest molecules.
The reaction of an aqueous solution of Mn(ClO4)2·6H2O with 5-fluoro-2-hydroxypyrimidine (HFpymo) and NaOH in 1:2:1 ratio affords a species analysing as Mn(Fpymo)2(H2O)2 (1) in 70% yield. Single crystal X-ray analysis reveals that 1 consists of [Mn2(μ-Fpymo-N1,O2)2(Fpymo-O2)2(H2O)4] dinuclear units, in which each Mn(II) ion shows a slightly distorted trigonal bipyramidal stereochemistry. Thermal treatment of 1 above 150°C gives an anhydrous, amorphous material analysing as Mn(Fpymo)2 (2a). Further heating of this compound above 250°C results in the formation of the microcrystalline Mn(Fpymo)2 species (2b). The thermal dependence of the magnetic susceptibility χ has been studied for species 1 and 2b in the 2–300K temperature range at 100, 300 and 5000Oe field strengths. The fitting of the χ values of 1 to the Curie–Weiss equation gives values of C=2.450(2) and θ=1.0(2)K, which is indicative of an almost negligible magnetic interaction between the Mn(II) centres. At variance, 2b shows a significant antiferromagnetic behaviour, with a decrease of the μeff values upon cooling. The fitting of the χ values of 2b to the Curie–Weiss equation gives the respective C and θ values of 4.26(1) and −14.8(3)K, which agrees with an efficient coupling of the magnetic Mn(II) centres, possibly through bridges of the Fpymo-N1,N3 kind, within a polymeric network. The N2 and CO2 gas adsorption measurements at 77K and 293K, respectively, show that the 2b phase is not microporous, which is reflected in its low BET surface (19m2g−1) and its BJH pore size distribution.
X-ray powder diffraction data for two ionic salts containing imidazole (Him) complexes of the magnesium(II) ion, [Mg(Him)4(H2O)2]Cl2 and [Mg(Him)6](NO3)2, are reported. Their crystal and molecular structures were determined by simulated annealing and full-profile Rietveld refinement methods. [Mg(Him)4(H2O)2]Cl2 was found to crystallize in the monoclinic system with space group C2/c, a=12.3980(3) Å, b=11.0234(2) Å, c=14.4691(3) Å, and β=107.024(1)°. [Mg(Him)6](NO3)2 crystallizes in the trigonal R-3 space group with a=b=12.4631(4) Å and c=14.9449(6)
Å. Both species contain centrosymmetric complexes, and Mg is octahedrally coordinated by six imidazoles, as in [Mg(Him)6](NO3)2, or by four imidazoles and two water molecules, as in [Mg(Him)4(H2O)2]Cl2. Additional analytic, thermogravimetric, calorimetric, and spectroscopic characterizations were also performed.
Three binuclear Cu(II) and Ni(II) perchlorate complexes with the potentially bidentate ligand 2-amino-6-methylpyrimidin-4(1H)-one (AMPO) [Cu(AMPO)4][Cu(H2O)5](ClO4)4·6H2O (1), [Cu2(AMPO)4(H2O)3](ClO4)4·½H2O (2) and[Ni(AMPO)4][Ni(H2O)6](ClO4)4·5H2O (3), have been prepared and were characterized by single crystal X-ray diffraction, IR spectroscopy and elemental analysis. Structural and IR data indicate that the ligand is present in its tautomeric form protonated at nitrogen in position one and metal coordinated at position three. The basic coordination pattern of the AMPO coordinated metal cations in all three complexes is square planar by four pyrimidyl nitrogen atoms of four different AMPO ligands. The coordination sphere is augmented by weak M⋯O interactions between the metal centers and AMPO keto oxygen atoms. Bond valence calculations indicate the M⋯O interactions to be most pronounced for nickel compound (3), and least for copper complex (2). The structural and geometrical differences between compounds (1) and (3) on the one hand and compound (2) on the other can to a large part be traced back to the lack of available water in the crystallization solvent in (2) which starves the cation not coordinated to AMPO nitrogen atoms of water molecules to saturate its coordination sphere, thus forcing two of the AMPO ligands in (2) to act as a bridging ligands, while the other AMPO ligands in the three structures are mostly monodentate with the coordination mode of the AMPO ligand being completed by weak secondary chelating M⋯O interactions.
The polymer {[Co(ox)(Htr)2]·2H2O}n (ox=oxalate dianion; Htr=1,2,4-triazole) (1) has been synthesized and characterized by FT-IR spectroscopy, thermal analysis, variable-temperature magnetic measurements and X-ray diffraction methods. The physical analysis allows us to propose a one-dimensional structure in which [Co(Htr)2]2+ units are bridged by bis-bidentate oxalato ligands. Magnetic measurements at variable temperature show an overall antiferromagnetic behavior of the compound. Isolated chains of this polymer have been obtained by sonication of 1 in water and deposition on mica or on mica treated with poly-l-lysine. Circular molecules and nano-fibres have been isolated on Highly Oriented Pyrolitic Graphite (HOPG) by casting deposition of sonicated solutions of 1 in ethanol. The direct reaction on HOPG surface between CoII, H2ox and Htr has proved a useful route to isolate one-dimensional systems on surfaces. The development of new strategies to characterize these types of polymers on surfaces opens the possibility to perform nano-scale studies on their properties and their potential use as nano-materials.
A class of intensely colored platinum complexes, derived from the hydrolysis product of the antitumor agent cisplatin, cis-[Pt(NH3)2(H2O)2]2+, and pyrimidine nucleobases (pym) and related cyclic or open amides, and generally
termed 'Platinum Blues', is discussed. First reported over 30 years ago, major questions concerning their nature have been solved since then, for example their mixed valency and paramagnetism. Their modes of action as antitumor agents and as nucleic acid stains remain elusive, however. It
has generally been assumed that the 'Blues' adopt linear chain structures, thus permitting short Pt•••Pt contacts, but more recent findings demonstrate that these ligands also allow cyclic structures to be formed (metallacalix[n]arenes). They provide a wealth of interesting
properties with regard to host–guest chemistry and non-covalent DNA binding. These developments are reviewed.
In the search for coordination compounds showing significant second harmonic generation (SHG) activity, reaction of Ag(I) ions with the 4-hydroxypyrimidine (4-Hpymo) and 5-nitro-2-hydroxypyrimidine (HNP) ligands generated four crystalline 1D polymers, Ag(4-pymo)·nH2O (n = 2.5, 0), Ag(NP)(NH3), and Ag(NP), the latter two crystallizing in acentric space groups. Their synthesis, complete characterization, and structural determination, by conventional single-crystal and laboratory X-ray powder diffraction methods, are presented and discussed in the frame of diazaaromatic-ligand- and metal-containing species. XRPD has also allowed the detection of the polyhydrated, elusive Ag(4-pymo)·nH2O (n = 2, 3) species. Powders of Ag(NP) have shown an SHG activity close to that of standard urea. By applying the geometrical model proposed by Zyss, it is shown that the NP ligand is a highly promising chromophore, the oxo and nitro functionalities cooperatively promoting a high hyperpolarizability.
Cited By (since 1996): 3, Export Date: 24 August 2012, Source: Scopus
Supramolekulare Koordinationsverbindungen haben mehrere Vorteile gegenüber ihren organischen Pendants: Sie sind in Eintopf-Reaktionen in hohen Ausbeuten zugänglich und weisen physikalische Eigenschaften auf, die organischen Molekülen in der Regel fehlen. Darüber hinaus ermöglichen ihre schwachen, reversiblen nicht-kovalent bindenden Wechselwirkungen die Behebung von Fehlverknüpfungen durch Selbstreparaturmechanismen. Dieser Aufsatz beschreibt Entwicklungen in der supramolekularen Koordinationschemie, die ausgehend von Zufallsentdeckungen mithilfe rationalen Designs gemacht wurden. Das Auffinden von Parallelen bei der Entstehung verschiedener supramolekularer Architekturen ermöglicht eine Vorhersage von Ergebnissen in ähnlichen Fällen. Die supramolekulare Synthese verläuft in etwa nach Regeln, wie sie das “lead sheet” zur Improvisation in einem kleinen Jazz-Ensemble vorgibt, und kann daher zu unvorhergesehenen Resultaten führen. Detaillierte Symmetriebetrachtungen haben basierend auf den Grundregeln der Koordinationschemie jüngst die Entwicklung rationaler Strategien für den Aufbau der verschiedensten Nanostrukturen mit geplanter Größe und Gestalt ermöglicht.
Sterically bulky pyrazines have been successfully utilized for the preparation of discrete oligo-nuclear TBP (trigonal bipyramidal), SqP (square pyramidal), and Oh (octahedral) copper(II) complexes. We have synthesized a unique linear pentanuclear complex [{Cu(hfac)2}5(μ-2-butyl-3-methylpyrazine)4]. The two terminal copper(II) ions have a SqP structure while the three inner ions have an Oh one. The solvent molecule was incorporated in the clearance of the lattice. From another reaction under harsh conditions, we separated [{Cu(hfac)2}3(μ-2-butyl-3-methylpyrazine)2], which can be regarded as the central moiety of the pentanuclear one. We also prepared a dinuclear complex [{Cu(hfac)2}2(μ-tetramethylpyrazine)], in which the pyrazine nitrogen atoms were located at TBP equatorial positions. Single-crystal EPR measurements supported its compressed TBP structure. The exchange coupling was antiferromagnetic with JTBP–TBP/kB=−3.6K. The linear trinuclear [{Cu(hfac)2}3(μ-2,3,5-trimethylpyrazine)2], having two TBP Cu ions with an intervening Oh Cu ion, showed very weak antiferromagnetic coupling. DFT calculations on these compounds indicated that the σ-type orbital overlap between the Cu and N atoms is essential for superexchange interactions.
Two unique bimetalic Pt(II) coordination polymers of composition [Ni(hydeten)2Pt(CN)4] (Ni–Pt) and [Cu(hydeten)2Pt(CN)4] (Cu–Pt) [hydeten=N-(2-hydroxyethyl-ethylenediamine) or 2-(2-aminoethylamino)ethanol] have been synthesized and structurally characterized by various methods in this study. The crystal structure of Cu–Pt was determined by single-crystal X-ray diffraction analysis. The structure of Cu–Pt forms of infinite 2,2-TT type [–Cu(hydeten)2–NC–Pt(CN)2–CN–] chains containing paramagnetic copper atoms bridged by tetracyanoplatinate species. In this complex, Cu(II) centers display an axially elongated octahedron with two chelating hydeten molecules in the equatorial positions and N-bonded bridging cyano groups in the axial positions, whereas Pt(II) centers are four coordinate with four cyanide-carbon atoms in a square-planar arrangement. The decrease of the moments of these complexes in temperature range of 50305K can assigned to the antiferromagnetic interactions in the structures. The thermal decomposition of Cu–Pt comprise of five distinguished stages, while the thermal decomposition of Ni–Pt take place four different stages.
Solution phase reaction of AgNO(3) with a mixture of benzene-1,3,5-tricarboxylic acid (H(3)BTC) and heterocyclic 2-aminopyrimidine (APYM) under the ammoniacal conditions gives rise to a novel metal-organic coordination polymer Ag(3)(BTC)(APYM)(2) (1). The structure of 1 possesses a unique three-dimensional (3D) framework with one-dimensional channels surrounded by carboxylato-supported Ag-Ag dimers, Ag-Ag chains, fully deprotonated [BTC](3-) and APYM ligands. Moreover, 1 exhibits strong blue photoluminescence maximized at 464 nm at room temperature (lambda(ex) = 383 nm) and upon cooling to 77 K, the emission spectrum seems narrowly red-shifted. (c) 2009 Elsevier B.V. All rights reserved.
The ultrasonic reactions of Ag(2)O with benzoguanamine and ancillary carboxylate ligands under the ammoniacal condition gave eight new coordination compounds (CCs), namely, [Ag(4)(bga)(6)(mal)(2)] (1), [Ag(4)(bga)(6)(mlc)(2)] (2), [Ag(bga)(2)(tpa)(0.5)](n) (3), {[Ag(bga)(suc)(0.5)]center dot C(2)H(5)OH}(n) (4), {[Ag(bga)(Pta)(0.5)]center dot CH(3)OH}(n) (5), {[Ag(bga)(ox)(0.5)]center dot C(2)H(5)OH center dot H(2)O}(n) (6), {[Ag(2)(bga)(2)(dnb)(2)]center dot DMF}(n) (7), and [Ag(2)(bga)(2)(pma)(0.5)(H(2)O)](n) (8) (bga = benzoguanamine, H(2)mal = malonic acid, H(2)mlc = maleic acid, H(2)tpa = terephthalic acid, H(2)suc = succinic acid, H(2)pta = phthalic acid, H(2)ox = oxalic acid, Hdnb = 3,5-dinitrobenzoic acid, H(4)pma = pyromellitic acid, and DMF = N,N'-dimethylformamide). All CCs have been characterized by elemental analyses, IR spectra, and single-crystal X-ray diffraction. Compounds 1 and 2 are OD discrete molecules and contain centrosymmetric [Ag(2)(mal)](2) and [Ag(2)(mlc)](2) units, respectively, which are extended to ID supramolecular chains through intermolecule N-H center dot center dot center dot N complementary hydrogen bonds. Compounds 3 and 4 contain similar ID [Ag(2)(tpa)](n) and [Ag(2)(suc)](n) infinite chains incorporating monodentate bga ligand as an ornament. It is noteworthy that the Ag center dot center dot center dot Ag interaction was exclusively observed in the ID chain of compound 4, which may be caused by different coordination environments of the Ag(I) center between 3 and 4. The Ag center dot center dot center dot pi interactions further extend the ID chains into 2D sheet in 4. In 5 and 6, the mu(2)-bga ligands link Ag(I) ions to form ID helical chains, which are further extended by mu(2)-dicarboxylate to 2D 6(3)-hcb net incorporating different dimensions of hexagonal grids. Compound 7 is a ID chain containing [Ag(2)(dnb)(2)] subunits, to which the monodentate and bidentate bga ligands as well as DMF coordinate. Compound 8 is a 2D sheet structure incorporating mu(6)-eta(1):eta(1):eta(1):eta(1):eta(1):eta(0):eta(1):eta(0) pma, monodentate and bidentate bga ligands. The results show that the structural diversity (0D-2D) of the CCs is mainly attributed to the usage of diverse ancillary carboxylate ligands as well as diverse coordination modes of bga ligand. Moreover, the photoluminescence properties of the CCs 1-6 were also investigated in the solid state at room temperature.
Eight new multidimensional metal(II) complexes [Zn(tp)2(NCS)2] (1), [Ni(tp)2(H2O)2(m-tp)2Ni(NCS)4]n (2), [Co(tp)2(H2O)2(m-tp)2Co(NCS)4]n (3), [Cd(tp)2(NCS)2]n (4), [Mn(tp)2(NCS)2(H2O)2] (5), [Zn(tp)2(NCO)2] (6), [Cd(tp)(NCO)2]n (7) and [Cd(tp)(N3)2]n (8) have been synthesized by conventional reactions of the 1,2,4-triazolo[1,5-a]pyrimidine with metallic(II) salts in the presence of thiocyanate, cyanate and azide as auxiliary ligands. X-Ray diffraction studies on these compounds show that species 1, 5 and 6 are mononuclear units in which zinc and manganese have tetrahedral and octahedral coordination geometry, respectively. Complexes 2 and 3 are isostructural and consist of neutral chains with triazolopyrimidine bridging ligands through N1, N3 nitrogen atoms. Compound 4 exhibits a 2D rectangular-grid-like structure and complexes 7 and 8 are cyanate-bridged chains formed by defective cubanes. Magnetic and luminescent properties of these materials have also been studied.
Reports on spontaneous self-assembly processes between metal fragments and organic ligands frequently tend to ignore the fact that the product isolated and structurally characterized in most cases is only one out of a more or less large series of feasible ones. This is true even for rings containing as few as three or four metal ions. Here we shall review metallatriangles and metallasquares containing predominantly cis-square-planar metal entities and a range of bidentate bridging ligands. The most significant features contributing to the number of possible stereoisomers appear to be ligand symmetry and flexibility, viz. rotation of two halves of a ligand about a single bond, or rotation of the whole ligand about the metal-donor atom bonds. With low-symmetry bidentate ligands the number of isomers increases dramatically with ring size as a consequence of an increase in possible connectivity patterns, hence linkage isomers, and an increase in possible rotamer states of the bridging ligands. In this tutorial review it is demonstrated how complexity increases as the symmetry of the bridging ligands is lowered from D(∞h) and D(2h) to C(∞v), C(2v), C(2h) and C(s). Special attention will be paid to cyclic tri- and tetranuclear complexes of substituted pyrimidine ligands (C(2v) and C(s) symmetries) as well as the flexible 2,2'-bipyrazine, which can adopt states of either C(2v) or C(2h) symmetry. Uses of these complexes and ways to reduce the number of isomers will be pointed out.
Conventional reactions of the versatile multidentate ligand 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (HmtpO) with metallic(II) salts lead to three novel multidimensional complexes [Cu(HmtpO)(2)(H(2)O)(3)](ClO(4))(2)·H(2)O (1), {[Cu(HmtpO)(2)(H(2)O)(2)](ClO(4))(2)·2HmtpO}(n) (2) and {[Co(HmtpO)(H(2)O)(3)](ClO(4))(2)·2H(2)O}(n) (3). In each compound, the triazolopyrimidine ligand shows a different and unusual coordination mode, giving rise to structures with diverse topologies and dimensionality. Compound 1 is a monomeric complex, in which HmtpO shows both N3-monodentate and N1,O71-bidentate modes. 2 is a bidimensional framework with the ligand showing a N3,O71 bidentate-bridging mode. The structure of 3 consists of 1D chains, in which HmtpO displays a N1,N3,O71-tridentate-bridging mode. It should be noted that these coordination modes of the HmtpO ligand are unique in the case of compounds 2 and 3. On the other hand, the magnetic properties of the polynuclear complexes 2 and 3 have been studied showing weak ferromagnetic and antiferromagnetic behaviour, respectively.
Pyrimidine (pym) ligands with their two endocyclic N-donor atoms provide 120° angles for molecular constructs, which, with the 90° angle metal fragments cis-a(2)M(II) (M=Pt, Pd; a=NH(3) or a(2)=diamine), form cyclic complexes known as metallacalix[n]arenes (with n=3, 4, 6, 8, …). The number of possible isomers of these species depends on the symmetry of the pym ligand. Although highly symmetrical (C(2v)) pym ligands form a single linkage isomer for any n and can adopt different conformations (e.g., cone, partial cone, 1,3-alternate, and 1,2-alternate in the case of n=4), low-symmetry pym ligands (C(s)) can produce a higher number of linkage isomers (e.g., four in the case of n=4) and a large number of different conformers. In the absence of any self-sorting bias, the number of possible species derived from a self-assembly process between cis-a(2)M(II) and a C(s)-symmetrical pym ligand can thus be very high. By using the C(s)-symmetric pym nucleobase cytosine, we have demonstrated that the number of feasible isomers for n=4 can be reduced to one by applying preformed building blocks such as cis-[a(2)M(cytosine-N3)(2)](n+) or cis-[a(2)M(cytosinate-N1)(2)] (for the latter, see the accompanying paper: A. Khutia, P. J. Sanz Miguel, B. Lippert, Chem. Eur. J. 2011, 17, DOI: 10.1002/chem.2010002723) and treating them with additional cis-a(2)M(II) . Moreover, intramolecular hydrogen-bonding interactions between the O2 and N4H(2) sites of the cytosine ligands reduce the number of possible rotamers to one. This approach of the "directed" assembly of a defined metallacalix[4]arene is demonstrated.
A molecular vase, analogous to a calix[4]arene, has been
generated from (en)PdII and 4,6-dimethyl-2-hydroxypyrimidine,
the X-ray crystallographic study showing that this compound is able to
incorporate a gadolinium atom.
Soft Supramolecular Materials (SSM) are multicomponent materials formed bythe bulk supramolecular assembly/aggregation of building units into a regularstructure, with stronger bonding within building units and weaker bondingbetween them. The nature of the building units may vary from simple moleculesto nanoparticles, and the forces linking the units together may vary from coordinativeto van der Waals. Recently SSM have attracted a great deal of attention due to theirwide variability, easy conversion from one structure to another, and active responseto external stimuli. It seems evident that the progress in the chemistry of SSMpredestines the appearance of a new generation of functional and ``smart'''' materials.
Molecular flasks of self-assembled M6L4 nanocages promote the [2+2] photodimerization of olefins in a surprisingly efficient fashion. Thus, the dimerization of acenaphthylenes and naphthoquinones quantitatively proceeded in the cavity with remarkable rate acceleration and perfect regio- and stereocontrol (>98 %, see scheme).
Louis Kahn, architect of the Salk Institute in La Jolla, said¹ “even a common, ordinary brick wants to be something more than it is.” Suppose that were also true of molecules. We know that they can and do aggregate; they give complex structures, and by doing so they acquire new properties—functions that may not be apparent from a study of the individual components. This review is about molecular aggregates of a certain sort, namely, those that assemble and more or less completely surround other molecules. Taking part in this intimacy imparts unique properties to the participants, and new functions emerge from the aggregate as a whole. For the most part, we emphasize self-complementary structures. Their ability to assemble—an expression of the molecule's desire to be something more than it is—results from instructions engineered into the molecules during their creation.
Reaction of p-tBu-calix[6]arene with potassium metal in methanol followed by [TiCp2Cl2] affords novel mononuclear and binuclear monocyclopentadienyl titanium(IV) complexes, both having the same inverted double cone conformation with a Cp in one of the cavities, in both complexes.
An experimental technique using powders is described which permits the rapid classification of materials according to
(a) magnitude of nonlinear optical coefficients relative to a crystalline quartz standard and
(b) existence or absence of phase matching direction(s) for second-harmonic generation.
Results are presented for a large number of inorganic and organic substances including single-crystal data on phase-matched second-harmonic generation in HIO3, KNbO3, PbTiO3, LiClO4·3H2O, and CO(NH2)2. Iodic acid (HIO3) has a nonlinear coefficient d14∼1.5×d31 LiNbO3. Since it is readily grown from water solution and does not exhibit optical damage effects, this material should be useful for nonlinear device applications.
The open “molecular box” [(en)Pt(U-N1,N3)]4 (1) (where en = ethylenediamine, U = uracil dianion) is able to act as an efficient ligand for additional metal ions. Reactions of the 1,3-alternate conformer of 1 with divalent metal ions result in the formation of octanuclear compounds of the general formula [(en)Pt(U-N1,N3,O2,O4)M]4X8 [M = Cu2+, X = Cl (2a), X = (SO4)0.5 (2b), and M = Co2+ (3), Ni2+ (4), Zn2+ (5) with X = (SO4)0.5], in which the heterometals are bound at the exocyclic oxygen atoms of the uracil nucleobases. The structurally characterized heteronuclear compounds show a 1,3-alternate arrangement of the uracil nucleobases. Pt–M contacts are in the range 2.743(2)–2.804(2) Å; the Pt atoms act as weak σ donors to the heterometals. In spite of the high degree of positive charge associated with compounds 2a–5, they do not behave as hosts for anions. This is a consequence of the orientation of the four nucleobases which, in contrast to a cone arrangement, does not produce a sufficiently large cavity for the incorporation of anions.
Reaction of Cu2+ salts with 4-hydroxypyrimidine (4-Hpymo) in water:ammonia (9:1) solutions at room temperature leads to formation of either [Cu(4-pymo)2(NH3)2(H2O)2] (1) or [Cu(4-pymo)2 · nH2O]∞ (2), depending on which crystal nucleation process occurs. Selective formation of 2 is possible by using non-coordinating Et3N as a base. X-ray diffraction analyses have been performed in both cases showing that 1 is a mononuclear compound in which the heterocyclic ligands monodentately coordinate the copper ions through the N1 nitrogen atom. 2 is a 3D sodalite type open framework, in which each 4-pymo ligand bridges two copper ions through both nitrogen atoms in the N,N′-exobidentate mode. Heating 1 at 110 °C in air generates an amorphous phase (2a), which shows the same chemical analysis and spectroscopic properties as dehydrated 2. Crystalline [Cu(4-pymo)2 · nH2O]∞ (2), possesses interesting physico-chemical properties related to its porous nature. Indeed, this material reversibly absorbs N2 and water vapour with minimal structural changes.
9-(5-Pyrimidinyl)anthracene (1) forms a ternary adduct 1·Cd(NO3)2·2(CH3OH), the crystal structure of which shows a remarkable cooperation of metal coordination, hydrogen bonding and aromatic stacking interactions in the hierarchical formation of one-, two- and three-dimensional networks. Ditopic pyrimidine ligands and cadmium ions form a pyrimidine–Cd2+ alternate copolymeric chain. The chains are held together to give a sheet by extensive cross-links via hydrogen bonding between metal-bound nitrate ions of one chain and methanol molecules of the neighboring one. The sheets are self-assembled via stacking, interpenetration or intercalation of the orthogonal anthracene side arms on both sides of a sheet. This gives rise to a layered structure having an alternate arrangement of inorganic and organic sheets; the former contains Cd2+ ions two-dimensionally networked by pyrimidine bridges and hydrogen-bonded nitrate–methanol links, while the latter is composed of tightly-packed anthracene columns.
The formation and X-ray structure of a cyclic, tetranuclear PtII complex of composition [{Pt(en)(uH)}4](NO3)4(uH = uracil monoanion) and its conversion into cyclic, octanuclear derivatives is reported.
Single-crystal X-ray analysis has shown the tetrameric structure of the low melting point product obtained from the base catalysed condensation of formaldehyde and para-t-butylphenol and its ability to form a stable cage-type clathrate with toluene.
The title compound, catena-poly[silver-mu-(2-pyrimidinolato-N:N') dihydrate], exhibits a case of pseudosymmetry, the supergroup being Aema (Cmce in standard setting) and the subgroup Pbca, identified a posteriori by trial and error. A considerable extinction effect is present, making the space-group assignment more difficult. The structure consists of infinite chains along the b axis, with alternating Ag atoms and 2-pyrimidinolate ligands. Each metal atom is placed at a false symmetry centre and is linearly coordinated by one N atom of each of two ligands. A false mirror plane passes through the middle of the organic moiety, which is attached to two Ag atoms via its two N atoms. The chains are linked by the water molecules, which are hydrogen bonded to one another and to the carbonyl O atoms, and also by direct Ag...Ag interactions.
Reversible encapsulation is one of the more recent forms of
molecular recognition. Small molecule targets are completely surrounded by
larger molecular assemblies and steric barriers keep the guest from
escaping the host. Calix[4]arenes make useful modules for capsule
construction and the review traces their history. Applications in physical
organic chemistry, materials science and spectroscopy are described.
Recrystallization
of 9-(5-pyrimidinyl)anthracene (1) with copper(II) nitrate trihydrate formed three
kinds of complexes: 1·Cu(NO3)2·H2O (2), 1·Cu(NO3)2·MeOH·H2O (3) and 1·Cu(NO3)2·2EtOH (4) by changing the recrystallization solvent. The crystal structure of the three complexes showed cooperation of metal coordination,
hydrogen bonding, and aromatic stacking interactions in the hierarchical formation of one-, two- and three-dimensional networks. Complexes 2 and 3 formed zigzag one-dimensional chains consisting of 1 and Cu2+ ions by
coordination of pyrimidine to Cu2+ ion in equatorial trans fashion. Complex 4 formed a spiral one-dimensional chain by coordination in equatorial cis fashion. The magnetic behavior of 2, 3, and 4 were measured on a SQUID
susceptometer to reveal that there existed strong antiferromagnetic interactions between Cu2+ ions. The
magnetic data of one-dimensional antiferromagnetic chains were analyzed by the Bonner–Fisher model. The antiferromagnetic
interaction between Cu2+
ions was around
−55 K,
which is the largest value observed in pyrimidine-bridged Cu2+
ions.
The combination of transition metal fragments with 90 or 180° angles, viz. cis-a2MII (a=amine or a2=diamine; M=Pt or Pd) and trans-a2PtII or HgII, respectively, with (heterocyclic ligands providing 90, 120, or 180° angles leads, either in a self-assembly process or in a stepwise fashion, to cations of versatile shapes and charges. Examples include open boxes, molecular squares, hexagons, triangles and cups. Intermolecular H bonding can assist association of smaller entities. Synthetic and structural aspects as well as physico–chemical properties of selected examples with be discussed.
A number of coordination polymers of the pymo ligand (Hpymo = 2-hydroxypyrimidine) have been prepared and fully characterized by chemical, spectroscopic, and thermal analyses. Their complete crystal structures have been solved ab initio from laboratory X-ray powder diffraction data and ultimately refined by the Rietveld method. The M(pymo)2 species (M = Co, Ni, Zn) consist of structurally related three-dimensional frameworks of very high thermal stability (decomposing under N2 only at T > 550 °C), with the metal atoms, linked by μ2-η1-η1 (N;N′) (Co, Zn) or μ2-η2-η1 (N,O;N′) bridges, about 5.4−5.7 Å apart. The hydrated species Ni(pymo)2(H2O)2.5 is based on a two-dimensional array of Ni(pymo)2 stoichiometry, containing both coordinated and clathrated water molecules, and can be selectively transformed into Ni(pymo)2 by thermal treatment, through an amorphous intermediate, recrystallizing at T > 315 °C. In contrast, one dimensional chains are found in the three hydrazine adducts, M(pymo)2(N2H4)2, which show unique bis(μ2-hydrazine) bridges (M···M ca. 4.0 Å) and terminally O-bonded pymo ligands.
Coordination networks that mimic silicate mineral structures are formed by a new class of coordination polymers, which are accessible through the self-assembly of tetrahedral copper(1) cations and bent, bifunctional pyrimidine ligands. Thus, extended organometallic framework can be produced, which show optical activity (as quartz), or microporosity (as zeolites)... or both! The first example of such a framework is [Cu(pyrimidine)2]BF4 which can be described as a 'stuffed feldspar', and contains channels that house both BF4 ions and disordered solvent molecules.
Zeolite type structures with large cages interconnected by multidimensional 12-ring (rings of 12 tetrahedrally coordinated
atoms) channels have been synthesized; more than a dozen large-pore materials were created in three different topologies with
aluminum (or gallium), cobalt (or manganese, magnesium, or zinc), and phosphorus at the tetrahedral coordination sites. Tetragonal
UCSB-8 has an unusually large cage built from 64 tetrahedral atoms and connected by an orthogonal channel system with 12-ring
apertures in two dimensions and 8-ring apertures in the third. Rhombohedral UCSB-10 and hexagonal UCSB-6 are structurally
related to faujasite and its hexagonal polymorph, respectively, and have large cages connected by 12-ring channels in all
three dimensions.
A hydrogen transfer potential is programmed into the components of a self-organising system, and cocrystallisation gives a molecular ribbon in which a triple hydrogen-bonding motif is reinforced by ion pairing.
This article deals with a coordination approach to
three-dimensional assemblies via
‘molecular
paneling’. Families of planar exo-multidentate organic ligands
(molecular panels) are found to assemble into large three-dimensional
assemblies through metal-coordination. In particular,
cis-protected square planar metals, (en)Pd2+ or
(en)Pt2+ (en = ethylenediamine), are shown to be very useful to
panel the molecules. Metal-assembled cages, bowls, tubes, capsules, and
polyhedra are efficiently constructed by this approach.
An achiral anthracene−pyrimidine derivative (5-(9-anthracenyl)pyrimidine, 1) forms adduct 1·Cd(NO3)2·H2O·EtOH (2) in chiral space group P21. The metal ion is hexacoordinated with two pyrimidine ligands (equatorial cis), water and ethanol (equatorial cis), and two nitrate ions (axial trans). The chirality arises from a pyrimidine−Cd2+ helical array and is preserved not only in each crystal via homochiral interstrand water−nitrate hydrogen bonding but also in all the crystals in the same chirality as a result of single-colony homochiral crystal growth. Compound 1 also forms achiral (Pbca) trihydrate adduct 1·Cd(NO3)2·3H2O (3) having nonhelical pyrimidine−Cd2+ zigzag chains. Achiral zigzag polymer 3 and chiral helical polymer 2 are interconvertible with each other in the solid states upon exchange of volatile ligands (ethanol and water). The helix winding associated with the conversion of adduct 3 to 2 can be made homochiral by seeding.
The preparation, X-ray crystal structure, and the solution behavior of a cyclic, tetranuclear nucleobase complex of (en)Pt(II), [(en)Pt(UH-N1,N3)]4(NO3)4 (2) (with en = 1.2-diaminoethane, UH = uracil monoanion, N1,N3 = platination sites) is described. The tetranuclear cation of 2 displays close similarities with calix[4]arenes as far as overall geometry and conformational behavior is concerned. The affinity of the metal analogue 2 for metal cations appears to be more pronounced as compared to typical calix[4]arenes, however. In the solid state, 2 adopts a 1,3-alternate conformation of the four uracil rings, but in solution and after deprotonation to [(en)Pt(U-N1,N3)]4 a second major species (cone conformer) occurs in solution. The assignment of this species is made on the basis of preliminary X-ray crystal data of a Ag4 derivative of 2, [(en)Pt(UH)Ag]4(NO3)8.4HO (3), in which the four uracil rings adopt a pinched-cone conformation and which, after Ag+ removal by means of Cl-, produces an identical species. 2 forms spontaneously in aqueous solution from the mononuclear precursor [(en)Pt(UH-N1)(H2O)](NO3).H2O (1). The analogous cis-[(NH3)2Pt(UH-N1)(H2O)](NO3) seems to behave similarly, although condensation products have not been isolated. In contrast, the N(3) linkage isomer cis-[(NH3)2Pt(UH-N3)(H2O)](NO3), prepared in situ from (cis-NH3)2Pt(UH-N3)Cl.2H2O(4) and AgNO3, does not form a cyclic tetramer under comparable experimental conditions but dimerizes only to a head-tail species with N3,O Pt coordination and a mu-OH complex, depending upon pH. Crystallographic data for the three structurally characterized compounds 1, 2, and 4 are as follows: 1, triclinic system, space group P1, a = 7.229(1) angstrom, b = 9.732(3) angstrom, c = 9.968(2) angstrom, a = 107.37(2)degrees, beta = 103.14(1)degrees, gamma = 99.46(2)degrees, Z = 2; 2, tetragonal system, space group P4(2)/n, a = 16.117(8) angstrom, b = 16.131(8) angstrom, c = 8.626(3) angstrom, z = 4; 4, monoclinic system, space group P2(1)/c, a = 6.592(14) angstrom, b = 20.135(25 ) angstrom, c = 7.493(10) angstrom, beta = 92.32(14)degrees, Z = 4. The cyclic tetramer 2 can be considered a prototype of a metal analogue of a calix[4]arene. Implications for the synthesis of other metal analogues of calixarenes and possible host-guest chemistry are briefly pointed out.
The thermally induced solid state transformation of the [Ag(pymo)]n·2nH2O 1D polymer, 1, shows separate dehydration (with amorphization, 2) and devitrification processes resulting in the cyclic [Ag(pymo)]6 oligomer, 3, which has been characterized by ab-initio XRPD analysis. This transformation is reversible, 3 → 1 being a rare case of ring-opening polymerization of a coordination compound.
Copper(II) bisimidazolate affords five different polymorphs; of these, one was structurally characterized 40 years ago by standard single-crystal X-ray diffraction (Jarvis, J. A. J.; Wells, A. F. Acta Crystallogr. 1960, 13, 1027), while the remaining four, selectively prepared as pure polycrystalline phases, have been now studied by X-ray powder diffraction (XRPD) methods. Of the four new (blue, green, olive-green, and pink) phases, three were solved by the ab initio XRPD technique and refined by the Rietveld method, and the fourth phase (pink) could not be structurally characterized. Crystal data for [Cu(imidazolate)2]n: blue phase, a = 27.559(3) Å, c = 5.3870(9) Å, trigonal, R3̄, Z = 54; green phase, a = 21.139(1) Å, b = 19.080(1) Å, c = 9.2842(8) Å, orthorhombic, Ccca, Z = 20; olive-green phase, a = 11.7556(8) Å, b = 23.422(2) Å, c = 9.0727(9) Å, β = 104.993(5)°, monoclinic, C2/c, Z = 12. All polymorphs contain four-coordinate CuN4 chromophores and (N,N‘)-exobidentate imidazolate ligands, but show different spectroscopic and structural properties, the latter ranging from 2D to different 3D networks of the PtS, sodalite, and moganite archetypes. The intermediacy of the [Cu(imidazole)2CO3]·H2O species in the synthesis of the blue polymorph has been confirmed by spectroscopic and thermal analyses. FTIR, Raman, and electronic spectra were correlated with the structural features revealed in the present work, and used to gain insight into the coordination geometry of copper(II) ions of the pink polymorph. In addition, the correct Raman spectrum for copper(II) bisimidazolate, common for all polymorphs, has been definitely determined.
Two new cobalt(II) species containing the pyrimidin-4-olate ligand (4-pymo) have been prepared and fully characterized by spectroscopic, thermal, and ab initio X-ray powder diffraction methods. The magnetic properties of both these species and Co(2-pymo)2, an extended cobalt(II) compound containing the pyrimidine-2-olate ligand (2-pymo), are also reported. Co(4-pymo)2(H2O)4 (1) [orthorhombic, Pcab, a = 13.5233(4) Å, b = 12.9617(3) Å, and c = 6.7925(2) Å] consists of D4h octahedral monomers, bearing axial 4-pymo ligands, interlinked by an extensive network of OH···X (X = O, N) hydrogen bonds. Upon heating, it loses water and transforms into an amorphous (above 150 °C) (2a) or a polycrystalline (above 320 °C) Co(4-pymo)2 phase (2b) [orthorhombic, Imma, a = 6.5720(8) Å, b = 6.6209(8) Å, and c = 20.688(2) Å]. In the latter, C2v pseudo-tetrahedral cobalt(II) ions are linked by 4-pymo ligands in the unusual N,O-exo-bidentate mode, generating 2D layers of nearly square meshes, thus significantly differing from the Co(2-pymo)2 analogue (3), in which N,N‘-exo-bidentate bridges generate an acentric, 3D diamondoid network. The thermal dependence of the magnetic susceptibility has been studied for all the above compounds (1, 2a, 2b, and 3) in the 2−300 K temperature range. The magnetic behavior of 1 is dominated by spin−orbit coupling of magnetically isolated octahedral Co(II) centers. The extended materials 2a and 2b show antiferromagnetic exchange between distorted tetrahedral metal centers, whereas 3 behaves as a spin-canted antiferromagnet, a ferromagnetic ordering taking place below a critical temperature, Tc = 23 K; 3 can thus be considered as a molecular magnet. Indeed, magnetic hysteresis studies on 3 at 4.8 K yield a coercitive field Hcoer = 3900 G and a remnant magnetization Mrem = 279 cm3 G mol-1.
The yellow, microcrystalline compound [Cu(pymo)] (Hpymo=2-hydroxypyrimidine) has been characterized with the newly emerging technique of ab initio X-ray powder diffraction. A unique and unprecedented crystal phase containing cyclic oligomers and infinite helical polymers (see picture) of the same monomeric fragment is selectively formed upon reaction of [Cu(CH3CN)4][BF4] and Hpymo with NEt3.
A [3+3] modular self-assembly gives rise to the formation of a molecular bowl or crown with syn,syn,syn conformation (see picture). These structures are analogues of calix[3]arenes and can function as anion receptors. Interestingly, an NO3- ion is found to distort from a trigonal plane into a trigonal pyramid when binding to the bottom of the molecular bowl.
The condensation reaction between p-tert-butylphenol and formaldehyde leads in a single step to good yields of cyclic oligomers in which, depending on the reaction conditions, either four, six, or eight phenol units are joined by methylene bridges. The beakerlike shape of the most stable conformation of the tetramer has led to their being given the name “calixarenes” (calix = chalice). Resorcinol can undergo condensation in a similar manner with a variety of aldehydes to afford cyclic tetramers with the same basic structure (the resorcarenes). In both cases the reaction does not require the use of dilution techniques, so that large quantities of product can be readily obtained. In addition, the parent compounds can be modified in various ways, in particular at the phenolic hydroxy groups or the phenyl residues; these approaches can be used separately or in combination. Calixarenes are thus ideal starting materials for the synthesis of various types of host molecules and can also act as building blocks for the construction of larger molecular systems with defined structures and functions. Their potential applications range from use as highly specific ligands for analytical chemistry, sensor techniques and medical diagnostics to their use in the decontamination of waste water and the construction of artificial enzymes and the synthesis of new materials for non-linear optics or for ultrathin layers and sieve membranes with molecular pores.
The goal of this chapter is to discuss the prevailing synthesis strategies for molecular sieves and highlight the interesting large pore structures that have emerged over the past decade or so. The chapter is divided into microporous and mesoporous materials followed by composition and pore size. The relevant details of structure, synthesis, and physicochemical properties for several important large pore molecular sieves are described in this chapter. An effort has been made to present the molecular sieve structures using both cylinder and space-filling models, in order to reveal the connectivity and realistic pore size in the same figure.
The development in the field of coordination polymers or metal-organic coordination networks, MOCNs (metal-organic frameworks, MOFs) is assessed in terms of property investigations in the areas of catalysis, chirality, conductivity, luminescence, magnetism, spin-transition (spin-crossover), non-linear optics (NLO) and porosity or zeolitic behavior upon which potential applications could be based.
The use of transition metals with low coordination numbers or blocked bonding positions in combination with nitrogen heterocyclic ligands of different geometries (e.g. pyrazole, imidazole, bipyrazine, pyrimidine or purine) leads to formation of both discrete supramolecular assemblies and 1D polymers. When highly coordinating ‘naked’ metal ions are applied instead, 2D and 3D frameworks are generated. Some of the assemblies, both molecular and polymeric, possess cavities or channels that can reversibly include guest molecules, including anions. The chemistry reported provides a vast playground for potential applications and future synthetic work.
Reaction of CuX2 (X ) NO3, Cl, (SO4)1/2) salts and Hpymo‚HX (Hpymo ) 2-hydroxypyrimidine; X ) Cl, NO3) in aqueous amine solutions (amine ) NH3, CH3NH2) leads to formation of the poorly crystalline three-dimensional open-framework coordination polymer [Cu(pymo-N1,N3)2]∞ (1). Under the same reaction conditions, but in the presence of amine and group 1 metal salts of single charged voluminous anions, highly crystalline clathrates of the type {[Cu(pymo-N1,N3)2]‚(AX)1/3}∞ (1‚AX with A ) NH4, CH3NH3, Li, K, Rb; X ) ClO4, BF4, PF6) are obtained. The X-ray crystal structure of 1‚NH4ClO4 reveals that the combination of square-planar Cu2+ ion with 120° bond angles provided by Hpymo generates a three-dimensional porous [Cu- (pymo-N1,N3)2]∞ framework with ammonium and perchlorate ions and water molecules included in the pores. 1 possesses a rich host-guest chemistry. Indeed, N2 sorption at 77 K by empty host 1 reveals its microporous nature with a BET surface area of ca. 200 m2 g-1. Hydrated 1 loses water upon heating and when exposed to moist air regenerates the original hydrated material. Likewise, 1‚NH4ClO4 loses ammonia upon heating, giving the corresponding activated acidic material 1‚HClO4 which upon exposure to gaseous ammonia regenerates 1‚NH4ClO4. In addition, 1 reversibly and selectively sorbs AClO4 salts (A ) NH4, Li, Na, K, Rb) when exposed to AClO4 aqueous solutions giving highly crystalline 1‚AClO4 clathrates. Cl-, NO3-, SiF62-, and SO42- salts are, however, not taken up. Salt sorption curves are of type V and possess hysteresis loops. This behavior agrees with the observed guest-induced structure phase change taking place in the 1 framework after guest inclusion.
Reaction of Cu(ClO4)2 with 4,6-dimethyl-2-hydroxypyrimidine (Hdmpymo) in aqueous amine solution gives rise to compounds of formula [L2Cu(dmpymo)](ClO4) (L=NH3, 1a; MeNH2, 1b). An X-ray crystallographic study on 1a revealed a 1-D polymeric structure in which dmpymo entities symmetrically bridge square planar copper(II) centres. The copper environment is made up of two ammonia and two nitrogen donor atoms from the pyrimidine ligands disposed in a trans configuration. Spectroscopic data (electronic spectra, EPR, IR) for 1a and 1b are very similar revealing their related nature. The magnetic properties of 1a have been investigated in the temperature range 2–300 K. A significant antiferromagnetic coupling with J=−23.0 cm−1, through the pyrimidine bridges, is observed by analysing the susceptibility data with the Hamiltonian H=−2JSiSi+1. Crystal data: orthorhombic, space group Pnma, a=13.676(3), b=10.804(2), c=9.528(2) AD , V=1407.8(5) AD 3, Z=4, Dcalc =1.681 g cm− 3, R=0.037 for 999 reflections.
Metal complexes of haxaazatriphenylene (hat) and its derivatives are reviewed, focusing on assembled structures based on their X-ray crystallographic structures. A wide variety of crystal structures of mononuclear, binuclear, trinuclear and oligonuclear complexes and coordination polymers are classified by the coordination modes such as bidentate, bis-bidentate, and tris-bidentate forms of the ligands, their synthetic procedures being developed from serendipitous to rational level. Their magnetic, electrochemical, photophysical properties, and molecular inclusions are described. The ligand, hat, discussed here is one of the most useful multifunctional ligands, affording not only various self-assembled frameworks but also unique electronic structures. Their characteristics are mentioned in detail.
Wall decoration: Coordinatively unsaturated metal centers (CuII, CoII, and NiII) can be embedded in the pore wall of a microporous coordination polymer containing Schiff base type metalloligands [M(salphdc)]2- (H4salphdc = N,N′-o- phenylenebis(salicylideneimine-5,5′-dicarboxylic acid)). These coordination polymers possess large 1D channels with dimensions of approximately 14 × 14 Å2 (see structure).
Molecular flasks of self-assembled M6L4 nanocages promote the [2+2] photodimerization of olefins in a surprisingly efficient fashion. Thus, the dimerization of acenaphthylenes and naphthoquinones quantitatively proceeded in the cavity with remarkable rate acceleration and perfect regio- and stereo-control (> 98%, see scheme).
Louis Kahn, architect of the Salk Institute in LaJolla, said "even a common, ordinary brick wants to be something more than it is". Suppose that were also true of molecules. We know that they can and do aggregate; they give complex structures, and by doing so they acquire new properties--functions that may not be apparent from a study of the individual components. This review is about molecular aggregates of a certain sort, namely, those that assemble and more or less completely surround other molecules. Taking part in this intimacy imparts unique properties to the participants, and new functions emerge from the aggregate as a whole. For the most part, we emphasize self-complementary structures. Their ability to assemble-an expression of the molecule's desire to be something more than it is--results from instructions engineered into the molecules during their creation.
Inorganic zeolites are used for many practical applications that exploit the microporosity intrinsic to their crystal structures. Organic analogues, which are assembled from modular organic building blocks linked through non-covalent interactions, are of interest for similar applications. These range from catalysis, separation and sensor technology to optoelectronics, with enantioselective separation and catalysis being especially important for the chemical and pharmaceutical industries. The modular construction of these analogues allows flexible and rational design, as both the architecture and chemical functionality of the micropores can, in principle, be precisely controlled. Porous organic solids with large voids and high framework stability have been produced, and investigations into the range of accessible pore functionalities have been initiated. For example, catalytically active organic zeolite analogues are known, as are chiral metal-organic open-framework materials. However, the latter are only available as racemic mixtures, or lack the degree of framework stability or void space that is required for practical applications. Here we report the synthesis of a homochiral metal-organic porous material that allows the enantioselective inclusion of metal complexes in its pores and catalyses a transesterification reaction in an enantioselective manner. Our synthesis strategy, which uses enantiopure metal-organic clusters as secondary building blocks, should be readily applicable to chemically modified cluster components and thus provide access to a wide range of porous organic materials suitable for enantioselective separation and catalysis.
Crystal engineering--the planning and construction of crystalline supramolecular architectures from modular building blocks--permits the rational design of functional molecular materials that exhibit technologically useful behaviour such as conductivity and superconductivity, ferromagnetism and nonlinear optical properties. Because the presence of two cooperative properties in the same crystal lattice might result in new physical phenomena and novel applications, a particularly attractive goal is the design of molecular materials with two properties that are difficult or impossible to combine in a conventional inorganic solid with a continuous lattice. A promising strategy for creating this type of 'bi-functionality' targets hybrid organic/inorganic crystals comprising two functional sub-lattices exhibiting distinct properties. In this way, the organic pi-electron donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) and its derivatives, which form the basis of most known molecular conductors and superconductors, have been combined with molecular magnetic anions, yielding predominantly materials with conventional semiconducting or conducting properties, but also systems that are both superconducting and paramagnetic. But interesting bulk magnetic properties fail to develop, owing to the discrete nature of the inorganic anions. Another strategy for achieving cooperative magnetism involves insertion of functional bulky cations into a polymeric magnetic anion, such as the bimetallic oxalato complex [MnIICrIII(C2O4)3]-, but only insoluble powders have been obtained in most cases. Here we report the synthesis of single crystals formed by infinite sheets of this magnetic coordination polymer interleaved with layers of conducting BEDT-TTF cations, and show that this molecule-based compound displays ferromagnetism and metallic conductivity.
A number of polymeric pyrazolato complexes have been prepared and characterized by spectroscopy, thermal analyses (DSC and TGA), and X-ray powder diffraction (XRPD) methods. Ab initio XRPD studies showed that the (isomorphous) [Zn(pz)(2)](n)() and [Cd(pz)(2)](n)() species (Hpz = pyrazole) are 1-D polymers containing tetrahedrally coordinated metals and M(&mgr;-pz)(2)M (M = Zn, Cd) bridges, much alike [Cu(pz)(2)](n)() [orthorhombic, Ibam, a = 7.4829(4), b = 14.3844(6), c = 7.3831(3) Å (Zn) and a = 7.8591(6), b = 13.652(1), c = 7.9165(4) Å (Cd)]; differently, Hg(pz)(2) [triclinic, P&onemacr;, a = 7.4097(3), b = 9.4474(3), c = 5.8345(3) Å, alpha = 96.310(2), beta = 96.752(3), and gamma = 73.694(2) degrees ] is best described as a mononuclear complex, containing two monodentate pyrazolato ligands loosely interacting, through long(er) Hg.N contacts with neighboring molecules. During the synthesis of the latter, an intermediate phase was obtained, and characterized as Hg(pz)NO(3), which contains a polymeric polycation, [Hg(pz)](n)()(n)()(+), based on Hg(&mgr;-pz)Hg bridges, and uncoordinated NO(3)(-) groups (orthorhombic, Pcmn, a = 17.2985(9), b = 5.2538(3), c = 7.3912(4) Å). All structures were ultimately refined by the Rietveld method.
The open "molecular box" [(en)Pt(UH-N(1),N(3))](4)(NO(3))(4) (with en = 1,2-diaminoethane, UH = uracil monoanion) resembles calix[4]arenes in its structure and solution dynamics. It adopts a 1,3-alternate conformation in the solid-state (1a), but in solution and after deprotonation to [(en)Pt(U-N(1),N(3))](4), a second major species (cone conformer (1b-4H(+))) occurs. 1b-4H(+) acts as an efficient ligand for additional metal ions through the oxo-surface formed by the four O(2) exocyclic atoms of the uracil nucleobases. As shown here, 1b-4H(+) can incorporate a single metal ion only, giving rise to the formation of species of type {[(en)PtU](4)M}(X)(n)() with M = Zn(II) (2a), Be(II) (3) (not isolated in the solid state), and La(III) (4); X = NO(3), SO(4)/2; n = 2, 3. In addition, both the protonated species of the cone conformer (1b, pH 2-4) and compounds 2a (at pH 3-8) and 3 (at pH 3-5) act as hosts for organic anions in water, as deduced from (1)H NMR studies. It is proposed that the cone conformers act as anion hosts due to a combination of positive charge as well as apolarity and size of the cavity. Host-guest complexes of type {[(en)PtU](4)Zn}(X)(NO(3),SO(4)/2) with X = p-toluenesulfonate (2b) and 3-(trismethylsilyl)-1-propanesulfonate (2c) included in the cone cavity have been prepared and association constants have been determined by (1)H NMR spectroscopy. The fact that 4 does not act as a host may be due to a possible tetradentate coordination of La to 1b-4H(+) which may result in a flatter cone cavity than in compounds 2 and 3.
The challenges and the opportunities in the field of crystal engineering were presented with the emphasis on supramolecular concepts. The supramolecular concepts were important for understanding the supramolecular isomerism and super structural diversity in the context of coordination polymers and organic molecular networks. These networks are based on the molecular components and the number and chemical type of components is restricted.
