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Synthesis of a Self-Assembled Molecular Capsule that Traps Pyridine Molecules by a Combination of Hydrogen Bonding and Copper(II) Coordination
Angewandte Chemie International Edition
Abstract
Copper(II) complexes of a tetradentate ligand self-assemble in pyridine to form two slightly different tetrameric units. Hydrogen bonding between the tetramers forms a capsular cavity that traps four molecules of pyridine (see picture).
... The synthesis of the H 2 hissal ligand was carried out by modifying the procedure reported earlier. 23 All four complexes 1−4 were obtained via a one-pot synthesis by stirring a methanolic solution of NiSO 4 ·7H 2 O, KHhissal, and a dipotassium salt of the respective dicarboxylates (in a 1:1:0.5 ratio) for 12 h at room temperature. In all four cases, the desired product was obtained from the evaporation of the filtrate (the solid by-product K 2 SO 4 insoluble in methanol is the precipitate) under reduced pressure. ...
... The H 2 hissal ligand was made by modifying a literature procedure. 23 However, its synthesis and characterization are reported in the Supporting Information. Physical Measurements. ...
Four new chiral supramolecular coordination networks of Ni(II) of general formula [Ni2(Hhissal)2(dicarboxylate)(H2O)2]·nH2O (where Hhissal = histidinesalicylate; dicarboxylate = adipate; n = 8 for 1, succinate; n = 4 for 2, maleate; n = 4 for 3, fumarate; and n = 6 for 4) are reported. On the basis of the single-crystal X-ray study, an unprecedented zig-zag chain structure of water octamer encapsulated in 1 has been identified. The supramolecular network of the dimetal subunits is formed through hydrogen bonding interactions between the amine N–H of Hhissal and the oxygen atom of the coordinated water molecule of one subunit with the uncoordinated oxygen atom and the coordinated oxygen atom of the carboxylate group of Hhissal of the next subunit, respectively. The strength of hydrogen bonding within this water cluster (the range of O···O distances is 2.702–2.760 Å) is similar to that found in ice. These networks are further characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction, polarimetry, UV–vis/diffuse reflectance and circular dichroism spectroscopy, and thermogravimetric analysis. A comparison of their properties indicates that these are isostructural with a variation of encapsulated water clusters.
... [9][10][11] Previous studies have utilized N-(2-hydroxybenzyl)-amino acids and N-(2-pyridylmethyl)-amino acids as useful polydentate ligands to form multidimensional and oligomeric structures. [12][13][14][15][16][17][18][19] Here we report the investigation of the influence of the amino N substituent in (2-pyridinylmethyl)amino ligands on the solid-state structure of copper(II) complexes. Depending on the substituent polymeric polynuclear [{Cu(µ-Cl)2(MeL1-κ 2 N,N')}n], dinuclear, [{CuCl(µ-Cl)(HL2-κ 2 N,N')}2] or mononuclear [CuCl2(HL3-κ 2 N,N',N'')] complexes were obtained. ...
The coordination behavior of three ligand precursors 2-[(2- pyridinylmethyl)amino]acetic acid hydrochloride, 4-[(2- pyridinylmethyl)amino]benzoic acid hydrochloride and 4-{[2-(pyridin-2- ylmethylamino)ethylamino]methyl}benzoic acid hydrochloride, HL1?HCl- HL3?HCl, respectively, in copper(II) complexes is described. The complexes were characterized by elemental analysis, ESI mass spectrometry and IR spectroscopy, as well as X-ray structural analysis. The reaction of copper(II) with HL1?HCl in methanol afforded the polymeric complex [{Cu(?-Cl)2(MeL1- ?2N,N?)}n] (1) featuring the methyl ester of L1 (MeL1). With HL2?HCl or HL3?HCl, the dimeric complex [{CuCl(?-Cl)(HL2-?2N,N?)}2] (2) or the mononuclear complex [CuCl2(HL3-?3N,N?,N??)] (3) were obtained. All complexes exhibited square-pyramidal geometries. In 1, polymeric chains are formed through bridging chlorido ligands without typical hydrogen bonding interaction. Contrarily, the COOH group in 2 is participating in the formation of intermolecular hydrogen bonding forming a supramolecular structure. In 3, intermolecular hydrogen bonding (Cl?O) leads to a 1-D polymeric structure. The copper(II) complex 2 diminished viability of human 8505C, MCF-7, 518A2 and SW480 cell lines. The tumoricidal effect of 2 was realized mainly through caspase-mediated apoptosis.
... Several structural studies have been carried out on transition metal complexes of the Schiff bases derived from condensation of salicylaldehyde and hydroxynaphthaldehyde with amino acids in view of the fact that these complexes can be used as non-enzymatic models analogous to the key intermediates in many metabolic reactions of amino acids such as transamination, decarboxylation, αand β-elimination, racimization, and intermediate products in biologically important reactions. [1][2][3][4][5] Derivatives of amino acids and pyridoxal or salicylaldehyde Schiff bases have been widely studied as a model systems for studying enzymatic processes. [6] A series of N-salicylaldeneglutamatocopper(II) complexes of composition Cu(sal-glu)X, where sal-glu represents Schiff bases derived from salicylaldehyde with L-and DL-glutamic acid and X = pyridine, 2-, 3-, and 4-methylpyridine, were prepared and characterized. ...
Ni(II) complexes with Schiff-bases obtained by condensation of glutamic acid with salicylaldehyde; 2,3-; 2,4-; 2,5-dihydroxybenzaldehyde and o-hydroxynaphthaldehyde have been synthesized using the template method in ethanol or ammonia media. They were characterized by elemental analyses, conductivity measurements, magnetic moment, UV, IR and H NMR spectra as well as thermal analysis (TG, DTG, DTA). The Schiff-bases are dibasic tridentate or tetradentate donors and the complexes have square planar and octahedral structures. The complexes decompose in two or three steps where kinetic and thermodynamic parameters of the decomposition steps were computed. The interactions of the formed complexes with FM-DNA were monitored by UV and fluorescence spectroscopy.
Four salts of an anionic iron(III) bis-complex, [Fe(LL-thr)2]1-, were synthesized from water or methanol. H2LL-thr is a tridentate ligand derived from the L-threonine amino acid, and the cations used are Li+ (1), Na+ (2), K+ (3), and Ba2+ (4). Single-crystal X-ray diffraction showed that all the complexes are coordination polymers of different dimensionalities. The iron(III) complex binds to cations through its coordinated phenolate and non-coordinated carboxylate oxygen atoms. While Li+ forms a linear chain, all others have a pair of bridged cations intervening the iron(III) complexes. The 3D network of Ba2+ salt has a sizeable solvent-accessible space occupied by aquated chloride ions. The differences in circular dichroism (CD) spectra and significantly lower conductance values in water and methanol support partial retention of the polymeric nature in methanol. The visible spectra of 4 in methanol or water showed an ∼10 nm shift of the charge transfer bands from 3. However, the addition of Al3+ salt to 2 showed a significant colour shift. Further investigation confirmed that the colour shift is due to partial protonation of the complex with protons generated from salt hydrolysis. Most reports on visual aluminium detection consider aluminium's binding as the shift's source. The present results show that protonation due to hydrolysis of aluminium salt can skew the observation.
Two coordination polymers [Cd(L)2(H2O)2]n (1) and [Cd(L)-µ2Cl]n (2) are synthesized from a L-methinone based reduced Schiff base ligand and characterized by various spectrochemical and analytical methods along with single-crystal X-ray analysis. The crystal structures indicate formation of a one-dimensional (1D) and a three-dimensional (3D) framework for 1 and 2 respectively. Controlled solid-state thermolysis of 1 and 2, resulted size specific CdS nanospheres (CdS-1/2) having hexagonal wurtzite structure with excellent optical properties. The photocatalytic activities of coordination polymers (1/2) as well as nanoparticles (CdS-1/2) are evaluated in degradation of methylene blue (MB) solution in presence of visible light which shows enhanced catalytic efficiency of nanoparticles over coordination polymers. Catalytic efficacy and reusability suggest the synthesized nanospheres can be used as potential photocatalysts for removal of hazardous organic wastes from water.
Chiral coordination polymers and porous chiral MOFs have great potential as agents for enantioselective separations, sensing, and catalysis due to their well-structured internal chiral cavities. They also have physical properties that may be exploited, such as non-linear optical activity, ferroelectrics, magnetochiral dichroism, and use as chemical shift reagents. There are many ways in which chiral coordination polymers can be synthesised and the file has grown tremendously over the past two decades. In this review, we will discuss some of the main synthetic approaches that have been taken towards this fascinating class of materials. The main focus will be placed on synthetic approaches using enantiopure ligands, the route that is most likely to yield homochiral network solids. We will highlight the applications of many examples, noting how the design of the frameworks influences their application. Whilst this is a mature field, there still lies huge potential for functional chiral materials, and we aim to demonstrate areas that are ripe for exploration.
The self‐assembly of a unique molecular container is reported: a hybrid hydrogen‐bonded/metal‐coordinated cage where both hydrogen‐bonding and metal‐coordination form the crucial part of the topology. The hybrid cage was prepared combining hydrogen‐bonded rosette motif and palladium(II)/platinum(II) coordination to a pyridine ligand. It was also shown that the hybrid cage could be prepared by integrative self‐sorting from simple components. For the first time the genuine dual character of the hybrid cage was manifested as both self‐assembling parts responded selectively to different stimuli (such as phosphine and cyanurate), which resulted in the disassembly of the cage.
A novel chiral Nickel (II) complex of N-(2-pyridylmethyl)-L-alanine (Hpyala) 1 has been prepared and structurally characterized by elemental analysis, FT-IR, UV-visible, TGA and single crystal X-ray diffraction techniques. Complex 1 crystallizes in an orthorhombic P212121 space group. The nickel (II) centre in the complex adopts a distorted octahedral geometry. This compound has been seen to exhibit structural diversity resulting from the number of lattice water molecules. The photoluminescent properties of this compound which have also been investigated, indicates the potential application in luminescence.
A reaction of 2-((pyridin-4-yl)methylamino)-4-(methylthio)butanoic acid (HL) and Zn(OAc)2.2H2O afforded a hexacoodinated coordination polymer of [Zn(L)(HL)(H2O)2]n (Zn-1). When the single crystals of Zn-1, are suspended in water-DMF (2:1) solution of Cu(OAc)2.H2O, a quantitative metal exchange occurred resulting an isomorphous structure [Cu(L)(HL)(H2O)2]n (Cu-1) via a single-crystal-to-single-crystal mediated route. The metal exchange process can be clearly monitored with visual colour change in solid state and supported by spectroscopic evidences. However, attempt to obtain Cu-1 via a direct reaction route under identical condition, afforded a completely different compound [Cu(L)(CH3COO)]n (Cu-2). Various counter ions of different Cu-sources as well as solvent types play an important role for the above metal exchange process. All the coordination polymers are unequivocally characterized by single crystal X-ray crystallography and other spectroscopic methods. The above metal exchange is unique as Cu-1 can be only synthesized by metal exchange route and follows the Irving–Williams series of stability for Cu(II) over Zn(II).
A novel metal-organic framework (MOF), namely, {[ZnL(bibp)]·2H2O}n (1) where H2L = 1-(4-Carboxy-benzyl)-5-oxo-pyrrolidine-2-carboxylic acid, bibp = 4,4′-bis(imidazol-1-yl)biphenyl, have been synthesized under solvothermal condition. In the reaction, the N-(2-carboxylbenzyl)-l-glutamic acid first undergoes intramolecular acylation to form 1-(4-Carboxy-benzyl)-5-oxo-pyrrolidine-2-carboxylic acid, which further reacts to form Compound 1. Its structure have been characterized by single-crystal X-ray diffraction analysis, elemental analysis, infrared spectroscopy and thermogravimetric analysis. Compound 1 exhibits a 3D framework with 5-fold interpenetrated dia topological network. In addition, dye adsorption experiment results indicated that compound 1 has good adsorption effect on methyl orange (MO) and can selectively adsorb and separate MO in a short time.
A series of Ni(II) complexes of L-methionine derived Schiff base ligand has been synthesized and their interconversions are investigated for the first time with the help of a variety of physico-chemical techniques. The different reactant/reagent conditions lead to mono- (1), di- (2a/2b) and tri-nuclear (3a/3b) Ni(II) complexes and they are unequivocally characterized by single crystal X-ray crystallography. Alkali ions K+/Na+ can serve as efficient templates for the conversion of 1 to tri-nuclear complex 3a/3b which are thermally stable at elevated temperature of 70 °C, but amenable to dissociation to 1 in the presence of strongly interacting 18-crown-6-ether. 2a gets transformed to 2b in DMF, in which the essential structural change is the incorporation of one DMF molecule to the coordination sphere of one of the Ni(II) centers with concomitant release of the coordinating thioether arm of the ligand. 2a and 2b can also be converted to self-assembled complex (3a/3b) by alkali metal salt addition at ambient temperature. Warming the solution to 70 °C dis-assembles the tri-nuclear complexes with a perceptible color change and this cycle can be repeated several times. Additional evidence for the inter-conversion and retention of all the complex species in solution is clearly established by ESI-mass and UV-Vis spectroscopy. Variable temperature magnetic analysis shows weak ferromagnetic and antiferromagnetic coupling for binuclear and self-assembly complexes respectively.
The trans-configured square-planar complex of dichloropalladium and chiral monodentate phosphine ligands forms self-complementary dimers through 16 hydrogen bonded amides and π-π stacking in chlorinated solvents. The self-assembly is controled by cis-trans isomerisation of the metal center, where trans-configuration governs the dimer formation.
The work describes an integrated optical platform forrecognition of Cr3+ at the picomolar level (0.66 pM). Thecondensation of a fluorene unit with L-leucine led to the development of a highly fluorescent molecular probe L which detects Cu2+ following a turn-off signaling mechanism. Further, the L-Cu2+ ensemble has been successfully utilized as a light-up signaling tool for selective turn-on sensing of Cr3+, for the first time, at the picomolar level through quencher displacement. This sensing process eventually detects selectively one paramagnetic cation through turn on signaling by the displacement of another paramagnetic cation. We have successfully shown that the common sensitivity issues associated with displacement approaches can be overcome by suitable ligand design. The present integrated system, L-Cu2+, has been found to be sensitive enough to detect Cr3+ at the picomolar level even in real samples, including water from different sources such as tap water, river water, and drinking water.
The work describes an integrated optical platform for recognition of Cr3+ at picomolar level (0.66 pM). The condensation of a fluorene unit with L-leucine led to the development of a highly fluorescent molecular probe L which detects Cu2+ following a turn-off signaling mechanism. Further, the L-Cu2+ ensemble has been successfully utilized as light-up signaling tool for selective turn-on sensing of Cr3+, for the first time, at picomolar level through quencher displacement. This sensing process eventually detects selectively one paramagnetic cation through turn-on signaling by the displacement of another paramagnetic cation. We have successfully shown that the common sensitivity issues associated with displacement approaches can be overcome by suitable ligand design. The present integrated system, L-Cu2+, has been found to be sensitive enough to detect Cr3+ at picomolar level even in real samples, including water from different sources such as tap water, river water and drinking water.
A tetranuclear nickel(II) complex featuring defective double-cubane of formula, [Ni4(L)2(C12H8N 2)2(CH3O)2(H2O) 2](ClO4)2 (1), where H2L is N-(3-methoxy-2-hydroxybenzyl)glycine has been prepared and structurally characterized. The structure of complex 1 consists of one [Ni 4(L)2(C12H8N2) 2(CH3O)2(H2O)2] 2+ cation and two perchlorate anions. The vertices of the two face-sharing defective cubanes are occupied by alternating nickel and oxygen ions and the four Ni(II) ions in the cluster are held together by two bridging μ3-CH3O- ions and four μ2- O- ions from two L2- ligands, forming a planar Ni 4 parallelogram. The complex 1 is further stabilized via intramolecular hydrogen bonds, generating a dimeric unit.
A new complex [Cu 2(sala) 2(H 2O) 2(4,4'-bipy)]·H 2O (sala = N-(2-hydroxybenzyl)-D,L- alaninate, 4,4-bipy = 4,4-bipyridine) has been synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction. The complex crystallizes in monoclinic system, space group C2/c with a = 42.44(3), b = 10.416(8), c = 15.487(13) Å, β = 97.455(14)°, C 30H 36Cu 2N 4O 9, M r = 723.71, V = 6789(9) Å 3, D c = 1.416 g/cm 3, Z = 8, F(000) = 2992, μ(MoKα) = 1.308 mm -1, R = 0.0493 and wR = 0.1004 for 4878 observed reflections (I > 2σ(I)). Structural analysis shows that each copper(II) atom displays a distorted square-based pyramidal coordination geometry with two oxygen atoms and one nitrogen atom from one N-(2-hydroxybenzyl)-D, L-alaninate, one nitrogen atom from 4,4-bipyridine ligand and one water molecule. 4,4-Bipyridine ligand bridges two Cu(II) ions to form a dinuclear compound. The molecular structure is extended into a one-dimensional wavy chain through hydrogen bonds. These 1D chains are further expanded into 2D networks through hydrogen bonds.
Four configurationally and conformationally related Zn(II) complexes with a tri- dentate ligand namely, N-(2-pyridylmethyl)-phenylalanine (Hpmpa), have been synthesized by hydrothermal reactions. [Zn(L-α-pmpa) 2-H2O] 1: orthorhombic, space group P212 12 with a = 15.1091(7), b = 16.2417(8), c = 5.9972(3) Å, V= 1471.70(12) Å3, Z = 2,Mr = 593.97, Dr = 1.340 gcm3, μ = 0.879 mm-1, F(000) = 620, R int = 0.0205, R = 0.0450 and wR = 0.1578 for 3102 observed reflections with 2δ(I); [Zn(D-α-pmpa)2-2H2O] 2: orthorhombic, space group P21212 with a = 15.1023(6), b = 16.2516(7), c = 6.0024(2) Å, V= 1473.21(10) Å3, Z = 2, Mr = 611.98, Dc = 1.380 g/cm3, μ = 0.882 mm -1, F(000) = 640, Rint= 0.0337, R = 0.0484 and wR = 0.1435 for 2408 observed reflections with I > 2δ(7); [Zn(L-β-pmpa) 2] 3: monoclinic, space group C2/c with a = 27.8667(5), b = 5.60350(10), c = 19.9636(2) Å,β = 120.2210(10)°, V= 2693.66(7) Å3, Z = 4, Mr = 575.95, Dc= 1.420 g/cm3, μ = 0.955 mm-1, F(000) = 1200, Rint 0.0345, = 0.0358 and wR = 0.1135 for 2251 observed reflections with I 27delta;(I); and [Zn(D-β-pmpa)2] 4. They are all mononuclear discrete structures. The influence of temperature and pH on the conformation of structures has been investigated. Moreover, the photoluminescent properties of compounds 1 and 3 are also reported.
A novel chiral coordination polymer, [Zn2 (C7H8O6)2 (4, 4′-bipy)2 (H2O)2]·4H2O (C7H8O6 = 2, 3-O-isopropylidene-L-tartrate, bipy = 4, 4′-bipyridine), was synthesized via a solvothermal reaction and characterized by elemental analyses, TG, IR and single crystal X-ray diffraction. The analysis results of crystal structure show that the complex is monoclinic with space group C2, a = 2.02334 (14) nm, b = 1.13896 (4) nm, c = 1.01091 (6) nm, β = 117.366 (3)°, V = 2.0689 (2) nm3. Both crystallographically unique Zn atoms exit as an octahedral geometry. The four equatorial positions of Zn1 atom are occupied by the carboxylate-oxygen atoms of the two tartrates, and the two oxygens of the left four carboxylate-oxygen atoms coordinate to two different Zn2 atoms, respectively, forming infinite coordination polymer chains. The left two of the trans equatorial positions of Zn2 atom are completed with two oxygen atoms of two water molecules. The axial positions of both Zn atoms are occupied by the nitrogen atoms from different 4, 4′-bipyridine molecules to give a 2D rectangular-grid layers with a cavity dimension of 0.51165 (3) nm × 1.13896 (5) nm. A three dimensional network is formed by the crystallization water chains joined by the carboxylate-oxygen atoms through hydrogen-bonding interactions.
Supramolecular chemistry of Schiff base ligands and their reduced homologues is rapidly growing and gaining increased attention due to their convenient and straightforward synthetic methods and a wide range of complexation modes with almost all types of metal ions. In fact, the phenomenon of molecular recognition, self-organization and self-assembly, and host–guest chemistry through covalent and noncovalent interactions is pivotal to the understanding and development of supramolecular chemistry. In this direction, several forms of acyclic and macrocyclic Schiff bases and their reduced forms are employed to gain more insights and correctly ascertain the effect of different donor atoms, their relative position, the number and size of the chelating rings formed, the flexibility, and the geometry around the coordinating moiety on the molecular recognition process and selective binding of cations, anions, and/or neutral species. In this connection, this chapter deals with the supramolecular and molecular recognition properties and interesting host–guest complexes and metalla–supramolecular network structures derived from several acyclic and cyclic Schiff bases and reduced Schiff base ligands. Various solid-state metalla-supramolecular network structures are delineated ranging from hydrogen-bonded linear polymers and helical coordination polymers, and 2D sheets to 3D network architectures constructed via N H⋯O, C O⋯H Osolvent, O H⋯O, N H⋯O C, hydrogen bonds and C O⋯π, C H⋯π, and π–π stacking interactions. This review gives an account of the observed structural diversity in relation to the role of different donors and acceptors, aqua ligands and solvents, nature of the ligands and metal ions, and the coordination geometry around the metal ions.Keywords:Schiff bases;acyclic Schiff bases;macrocyclic Schiff bases;salens;reduced Schiff bases;molecular recognition;host–guest chemistry;cation binding;anion binding;water chains;hydrogen bond;coordination polymers
Molecular capsules, cages and other three-dimensional hosts arising from the reversible assembly of complementary monomers are able to enclose space and encapsulate guest molecules. This article highlights work done in this area exemplifying the growing variety of non-covalent stabilising interactions being employed in host formation. These interactions include hydrogen bonding, ionic interactions, metal ion coordination as well as combinations thereof. Due to the protective environment offered by these hosts from the bulk phase solution, altered properties are often observed for encapsulated guests which is paving the way towards realising practical applications of such host systems.
Through the strategic design of ligands based on amino acids, structural diversity in chiral coordination architectures of Cu(II) is demonstrated with six new examples: {[Cu(l-HTyrbenz)2]·CH3OH·H2O}n (), {[Cu(l-HSerbenz)2]·3H2O}n (), {[Cu(l-HTyrthio)2]·H2O}n (), [Cu(l-HTyr4-pyr)2(H2O)]·2H2O (), [Cu(l-HSerthio)2(H2O)] (), and [Cu(l-Phethio)2(H2O)]·3H2O () [where l-H2Tyrbenz = l-N-(benzyl)-tyrosine, l-H2Serbenz = l-N-(benzyl)-serine, l-H2Tyrthio = l-N-(methyl-2-thiophenyl)-tyrosine, l-H2Tyr4-pyr = l-N-(methyl-4-pyridyl)-tyrosine, l-H2Serthio = l-N-(methyl-2-thiophenyl)-serine and l-HPhethio = l-N-(methyl-2-thiophenyl)-phenylalanine]. For these 1 : 2 metal-ligand complexes, the availability of a donor atom (either from the phenolic OH group or the carboxylate group of one of the ligands) for bridging between the Cu(II) centers results in the formation of coordination polymers (), while no such availability allows a water molecule to occupy the fifth site around the Cu(II) center to generate hydrogen bonded supramolecular assemblies (). In , a coordination polymer is formed via a syn-anti bridging carboxylate, and the phenolic group has no role in its formation. To further emphasize this point, l-tyrosine in is replaced with l-serine to form , in which an anti-anti bridging by the carboxylate group is observed. On the other hand, the formation of {[Cu(l-HTyrthio)2]·H2O}n () results from the growth of a spiral polymer via the unique phenolic bridging with a distance of 10.806(9) Å between two Cu(II) centers. On changing from the l-H2Tyrbenz ligand to the l-H2Tyr4-pyr ligand (vs.), the strong hydrogen bonding of the pyridyl nitrogen with the phenolic group does not allow the latter to bind to Cu(II). Similarly, on changing from l-H2Tyrthio to l-H2Serthio (vs.), the length of the -CH2OH group in the latter is much less than the distance between the two Cu(II) centers, therefore this group cannot occupy the fifth site and thus a water molecule is coordinated. This is further confirmed by reacting with 2 eq. of l-H2Tyrthio in methanol to form , while the reverse is not possible. All these compounds are characterized by a number of analytical methods, such as elemental analysis, FTIR, UV-Vis and circular dichroism spectroscopy, polarimetry, powder and single crystal X-ray diffraction and thermogravimetric analysis. Photoluminescence properties of all ligands containing the l-tyrosine group and their metal complexes (, and ) are compared in solution at room temperature.
New zinc(II) and copper(II) complexes with a reduced Schiff-base ligand derived from D,L-selenomethionine and salicylaldehyde have been synthesized and characterized by elemental analysis, magnetic susceptibility, IR, and NMR measurements. The single-crystal X-ray structure of the Cu(II) complex reveals that this complex is a carboxylate-bridged dimer of dinuclear copper(II) subunits and all metal centers are five-coordinate with O4N donor sets in distorted square-pyramidal geometries. The Cu(II) complex consists of a 1-D coordination polymer.
Highlights of the year's literature include the first complex containing a copper–bismuth bond, the first mixed valence CuI/II alkoxides, and evidence of non-redox roles for the CuB site in cytochrome c oxidase. The biologically-important {CuIII(μ-O)2}22+ core has been identified in copper-exchanged ZSM-5, which also catalyses efficiently the one-step oxidation of benzene to phenol. Important developments in the Jahn–Teller distortion of copper(II) compounds have been reviewed; bond-stretch isomerism has been identified and the alternation of elongation axes discussed in Jahn–Teller active systems.
Three new metal complexes were synthesized by reactions of [bis(2-amino-ethyl)-amino]-acetic acid (HL) and different metal salts at different pH values. Their structures were characterized by X-ray crystallography. Interestingly, under acidic conditions, the dinuclear structure {Cu2[H(L)]2Cl2}(ClO4)2 (1) was obtained, whereas under alkaline conditions, the complexes {[Cu(L)](ClO4)}n (2) and [Cd(L)Cl]n (3), which exhibit distinct one-dimensional (1D) structures, were obtained. The results indicate that the pH value, metal ions, and anions have remarkable influence on the formation and structure of the complexes.
We are reporting structural characterization of two new hexanuclear cages (H3O)2[Cu3(μ3-OH)(μ3-NH3)0.5(L)3]2·8H2O (1) and (H3O)2[Cu3(μ3-OH)(μ3-H2O)0.5(L)3]2·8H2O (1a) where L2− is the dianionic form of the Schiff base of L-alanine and salicylaldehyde. The complex 1 has two C3 symmetric hydroxo bridged trinuclear halves joined by an ammonia or water molecule at the center through H-bonding. Each of the trinuclear halves is enantiopure but of opposite chirality to the other half, making the hexanuclear unit a meso isomer. Temperature dependent magnetic measurements showed the presence of ferromagnetic interactions among trinuclear Cu(II) units, a rare occurrence among trinuclear Cu(II) complexes. Characterization of the LiHL showed it to be enantiopure. Addition of a base, monitored using optical rotation, showed that racemization occurs as a result of base addition. The racemization depends on the base as well as the temperature. Base or Cu(II) induced racemization of amino acid derivatives has been indicated in a number of cases in the past but structural characterization of the products or formation of this type of chiral hexanuclear architecture was never reported. Structures of the complex and the ligand have a number of interesting H-bonding situations.
N-(2-Pyridylmethyl)-L-alanine (L-Hpana), and N-(2-pyridylmethyl)-aspartic acid (L-H(2)pasp) have been solvothermally prepared and structurally characterized by X-ray single-crystal diffraction. Complexes 1 and 2 crystallize in the monoclinic P2(1)/c and orthorhombic C222(1) space groups, respectively, due to the dissimilar ligand features (chirality of L-Hpana). They show similar mononuclear coordination structures with two kinds of five-member chelating rings, which are assembled into 2D supramolecular networks through multiple N-H center dot center dot center dot O and O-H center dot center dot center dot O interactions. For complex 3, the formation of a Ni-O bond between Ni(II) and the side-chain carboxylate lead to a left-handed helical coordination polymer with helical water chains inclusion. The most striking feature is that the helical hydrogen-bonding motif represents rare hydrated hydronium aggregation that formed by strong interactions between hydronium ions and guest water molecules. This helical aggregate is further stabilized by multiple hydrogen bonds with other lattice water molecules and chloride counteranions. The thermal and luminescent properties of these complexes have also been investigated.
A chiral supramolecular architecture, [Cu 2(4,4'-bipy)
2(sala) 2] n·4.5nH 2O
( 1) (sala= N-(2-hydroxybenzyl)- L-alanine anion), has been synthesized
by the reaction of Cu(NO 3) 2·2H
2O with 4,4'-bipyridine (4,4'-bipy) and N-(2-hydroxybenzyl)-
L-alanine (H 2sala) in basic ethanol/aqueous solution. X-ray
single crystal diffraction analysis reveals that complex 1 has a 3D
extended structure in which the mononuclear anions [Cu(sala)
2] 2- are bonded to [Cu(4,4'-bipy) 2]
2+ cations through Cu-O bond at a distance of 2.528 Å.
One Cu(II) center is in lengthened octahedral geometry and another one
is in planar square environment. The cyclic voltammetry shows that two
Cu(II) centers have different electrochemical properties.
The title compound, [Cd(C11H11NO5)(H2O)(2)]., crystallizes in orthorhombic, space group Pbca with a = 8.521(3), b = 10.154(3), c = 28.804(8) angstrom, V = 2492.2(13) angstrom(3), Z = 8, C11H15NO7Cd,M-r= 385.64, D-c= 2.056 g/cm(3), F(000) = 1536, mu(MoK alpha) = 1.786 mm(-1), the final R = 0.0424 and wR = 0.0859 for 2026 observed reflections with I > 2 sigma(I). It has a one-dimensional zig-zag chain structure along the a axis driven by Cd-O coordination bonds. Three kinds of hydrogen bonds connect the chains along the b axis into a two-dimensional structure.
A series of water-soluble platinum(II) complexes of reduced amino acid Schiff bases were synthesized as potential anticancer agents and characterized by 1H NMR, EA, MS, IR, and molar conductivity. These compounds were tested for their DNA interaction with salmon sperm DNA, and their in vitro anticancer activities have been validated against HL-60, KB, BGC-823, and Bel-7402 cell lines by the MTT assay. The cytotoxicity of one complex (5g) is better than that of cisplatin against BGC-823 and HL-60 cell lines, and show close cytotoxic effect against Bel-7402 cell line.
Graphical Abstract
Two new reduced Schiff base ligands, [HL1 = 4-{2-[(pyridin-2-ylmethyl)-amino]-ethylimino}-pentan-2-one and HL2 = 4-[2-(1-pyridin-2-yl-ethylamino)-ethylimino]-pentan-2-one] have been prepared by reduction of the corresponding tetradentate unsymmetrical Schiff bases derived from 1:1: 1 condensation of 1,2-ethanediamine, acetylacetone and pyridine-2-carboxaldehyde/2-acetyl pyridine. Four complexes, [Ni(L1)]ClO4 (1), [Cu(L1)]ClO4 (2), [Ni(L2)]ClO4 (3), and [Cu(L2)]ClO4 (4) with these two reduced Schiff base ligands have been synthesized and structurally characterized by X-ray crystallography. The mono-negative ligands L1 and L2 are chelated in all four complexes through the four donor atoms to form square planar nickel(II) and copper(II) complexes. Structures of 3 and 4 reveal that enantiomeric pairs are crystallized together with opposite chirality in the nitrogen and carbon atoms. The two CuII complexes (2 and 4) exhibit both irreversible reductive (CuII/CuI; Epc, −1.00 and −1.04 V) and oxidative (CuII/CuIII; Epa, +1.22 and +1.17 V, respectively) responses in cyclic voltammetry. The electrochemically generated CuI species for both the complexes are unstable and undergo disproportionation.
A series of metal complexes containing the 4-methylumbelliferone-8-methyleneiminodiacetic acid (H3muia, also named as Calcein Blue) has been synthesized and characterized. Complexes of Cu(II), Ni(II), Mn(II), Zn(II) and Mg(II) have been structurally characterized while Ca(II) and Al(III) complexes by elemental analysis and thermogravimetry. The Cu(II) and Ni(II) complexes are neutral and mononuclear in the solid state. Interestingly, the Mn(II), Zn(II) and Mg(II) muia complexes exist as ion-pairs containing hydrated or solvated metal cation and dimeric metal(II) muia anions. Owing to the presence of hydrogen-bond donors and acceptors in the ligand, hydrogen bonding interactions are dominant along with π–π stacking in their solid-state structures. The solid-state fluorescence studies indicate that the family of muia complexes exhibit comparable emission properties as in solution state, in which only main group and post-transition complexes show bright blue fluorescence while transition metal complexes do not fluoresce.
Complexes [Cu(HSas)(H2O)] · 2H2O (H3Sas = N-(2-hydroxybenzyl)-l-aspartic acid) (1), [Cu(HMeSglu)(H2O)] · 2H2O (H3MeSglu = (N-(2-hydroxy-5-methylbenzyl)-l-glutamic acid) (2), [Cu2(Smet)2] (H2Smet = (N-(2-hydroxybenzyl)-l-methionine) (3), [Ni(HSas)(H2O)] (4), [Ni2(Smet)2(H2O)2] (5), and [Ni(HSapg)2] (H2Sapg = (N-(2-hydroxybenzyl)-l-aspargine) (6) have been synthesized and characterized by chemical and spectroscopic methods. Structural determination by single crystal X-ray diffraction studies revealed 1D coordination polymeric structures in 2 and 4, and hydrogen-bonded network structure in 5 and 6. In contrast to previously reported coordination compounds with similar ligands, the phenol remains protonated and bonded to the metal ions in 2 and 4, and also probably in 1. However, the phenolic group is non-bonded in 6.
The reaction of Zn(ClO4)2 · 6H2O and Cu(ClO4)2 · 6H2O with H3Sas (H3Sas = N-(2-hydroxybenzyl)-L-aspartic acid in water afforded the complexes [Zn6(Sas)4(H2O)8]·5H2O (1) and [Cu(HSas)(H2O)] (2), respectively, which were characterized by infrared spectroscopy, elemental analysis, thermogravimetry and single-crystal X-ray crystallography. In 1, the pentanuclear clusters formed by four H3Sas ligands and five Zn(II) metal ions are bridged by the “[Zn(H2O)4]2+” cations to form 1D polymeric chains. While in 2, the mononuclear [Cu(HSas)(H2O)] repeating units form a 1D zigzag chain and further extended by strong intermolecular hydrogen bonds to form a 2D sheet. The different coordination geometries of Cu(II) and Zn(II) show significant influence on the polymeric structures.
Six homochiral metal–organic coordination networks based on two new phenyl acid-amino acids, [ZnL12(H2O)2] (1), [Cu2L12(H2O)3] (2), [Zn2L12] (3), [CuL2(H2O)2]·2H2O (4), [ZnL2] (5) and [Cd3NaL23(ClO4)]·3H2O·DMF (6), where L1 = (S)-4-((1-carboxy-2-methylpropylamino)methyl)benzoic acid, and L2 = (S)-4-((1-carboxy-2-hydroxyethylamino)methyl)benzoic acid, have been synthesized and characterized. Compound 1 is a supramolecular network of hydrogen bondings linking up discrete zinc coordination units, and compound 2 presents a 2D lattice motif of water molecules linking up polymeric chains, while compound 3 is a 3D network constructed of interesting left-hand triple helices. Compound 4 consists of 1D coordination polymeric chains, while compound 5 adopts an intriguing 2D diamondoid network built from two kinds of left-handed helices, and compound 6 is a 3D framework constructed from homochiral cages. In addition, the second-order nonlinear optics (NLO) properties of compounds 1–6 were investigated. Compound 1 has a powder SHG intensity of 3.4 versus a-quartz, and the powder SHG intensities of compounds 2–4 approximate to that of a-quartz, while the powder SHG intensities are 7.8 and 8.4 versus a-quartz for compounds 5 and 6, respectively. Compounds 1, 3, 5 and 6 in the solid state exhibit blue fluorescent emissions at room temperature, mainly attributed to the ligand-centered transitions.
A series of Ni2+ complexes of N-(7-hydroxy-4-methyl-8-coumarinyl)-glycine (H2mugly) and N-(7-hydroxy-4-methyl-8-coumarinyl)-L-alanine (H2muala) has been prepared by self-assembly of Ni(CH3COO)2·4H2O with ligands in the presence of alkali metal ions. The complexes have been characterized by elemental analysis, thermogravimetry, IR and ESI-MS studies, and several of these complexes have also been structurally characterized by X-ray crystallography. Interestingly, the alkali metal ions have been found to direct the self-assembly processes and facilitate the formation of oligonuclear structures. Structural investigations showed that the molecular clusters displayed intriguing architectures including heptanickel metallocrowns with highly symmetrical hexagonal shapes, a heterobimetallic molecular cage and a pentanickelcluster with a nanobasket shape. The diversity of the coordination geometries and the cluster structures are discussed in detail.
A series of copper-L-arginine complexes has been synthesized and characterized by spectroscopic and single-crystal X-ray diffraction analyses. The L-arginineSchiff bases invariably show [ONO] tridentate coordination on a mononuclear Cu(II) sphere. [Cu(RNap)(OAc)]·2H2O, 1 (RNap = N-(2-hydroxy-1-naphthalidene) L-arginine), obtained from Cu(OAc)2·2H2O and HRNap, gives two stereochemically different molecules in the crystal unit cell, with each of them showing different acetate binding modes. It exhibits a channel structure with disordered water molecules filling the cavity. Complexation of N-(2-hydroxy-5-nitro-1-salicylidene) L-arginine (HRNO2) with Cu(ClO4)2·6H2O yields the intriguing triclinic crystal structure of 2. Its unit cell consists of a neutral molecule [Cu(RNO2)Cl(H2O)], an ion pair [Cu(RNO2)(H2O)2]ClO4 and three water molecules of crystallization. Complexation of HRMe (RMe = N-(2-hydroxy-5-methyl-1-salicylidene) with Cu(OAc)2·2H2O gives [Cu(RMe)(OAc)]·5H2O, 3, whose crystal packing shows a zeolite-like network with a watercluster residing in the hydrophilic channel, thus facilitating the hydrogen bonding interaction.
Four pentacoordinated square-pyramidal Cu(II) complexes with the general formula [Cu(L)(X)], where L is a l-histidine derived tetradentate ligand and X is either 3-hydroxypyridine or 2-methylpyridine, has been synthesized. Structural analysis showed that the presence of water filled one dimensional chiral channel in the lattices. The interiors of the channels were varied using aromatic ring substitution on the ligand as well as on the monodentate ligand. The dimensions of the channels range from ∼7 to 9Å.
There are an ever increasing number of interesting and complex supramolecular architectures being designed and isolated. However, a slight shift is detected towards an increasing focus on the application of the supramolecular concept to the area of functional materials, sensors and components for molecular electronics and nanofabrication. An ultra-large {Mn84} wheel-shaped cluster has been isolated that is a single-molecule magnet (SMM). Many new types of cluster frameworks have been synthesized, some notably (e.g. Fe14) using hydrothermal methods. Polyoxometalate clusters provide paradigms for cation capture and filtering, whereas ligand design has allowed access to a vast range of molecular grids, cubes, boxes and other complexes with interesting functionality e.g. solvatochromism, Zn(II)-sensors and a nanovalve.
Four new layered transition-metal hydroxyl−carboxylate−phosphonates, [M(CH(OH)(CO2)(PO3H))(H2O)2] (M = Mn (1), Fe (2), Co (3), Zn (4)), have been successfully hydrothermally synthesized and characterized by single-crystal X-ray diffraction as well as with elemental analysis, infrared spectroscopy, thermogravimetric analysis, and magnetic measurement. These isomorphous compounds crystalline in the monoclinic space group P21/c with a = 5.678(2)−5.800(2) Å, b = 15.469(6)−15.664(5) Å, c = 7.846(3)−7.911(2) Å, β = 109.287(4)−110.332(3)°, V = 649.5(4)−676.5(4) Å3, and Z = 4. In these compounds, transition-metal [MO6] (M = Mn, Fe, Co, Zn) octahedra and [PCO3] tetrahedra are connected to each other through corners into an infinite wriggled chain. Carboxylate and hydroxyl groups interlace the chain to form an organic−inorganic hybrid layered structure. The results of magnetic measurements revealed the presence of antiferromagnetic interactions of M(II) ions (M = Mn, Fe, Co) in compounds 1−3, respectively.
Four different mononuclear octahedral Ni(II) complexes with protonated and deprotonated form of the same ligand have been synthesized by controlling reaction conditions and structurally characterized. The complexes are [Ni(HLl-his)(benzoate)(MeOH)] (1), [Ni(HLl-his)(SCN)(MeOH)] (2), [Ni(HLl-his)2] (3) and [Ni(Ll-his)(imidazole)2] (4) where H2Ll-his is (S)-2-(2-hydroxybenzylamino)-3-(1H-imidazol-4-yl)-propionic acid. The ligand behaves as a monobasic tetradentate ligand in 1 and 2, monobasic tridentate ligand in 3 and dibasic tetradentate ligand in 4. Ni(II) coordinated phenolic proton of the ligand in the complexes 1–2 shows strong intra-molecular H-bonding with benzoate in 1 and lattice water in 2, whereas 3 shows intermolecular H-bonding between uncoordinated phenols with neighbouring carboxylate. The pH titration of the complexes revealed that metal coordination and H-bond in complexes 1 and 2 considerably lowers the acidity of ligand phenol (pKa 6.8 and 7.0 respectively) compared to phenol (pKa 10). The complex 4 does not show any proton loss due to the absence of phenolic proton. All the complexes show extensive H-bonded network in the crystals including narrow (7.8×5.2Å) water filled one dimensional channel in 2.
Metal coordination compounds derived from several closely related yet different multidentate reduced Schiff base ligands (obtained by reducing the CN bond in the Schiff bases formed by the condensation of aldehyde and various natural/unnatural amino acids) are discussed in terms of their mode of binding and coordination to supramolecular network structures. These multidentate ligands have flexible backbone with hydrogen bond donors and acceptors, and readily form metal complexes and coordination polymers with metal ions such as Cu(II), Zn(II), and Ni(II). Various solid-state metallasupramolecular network structures are delineated ranging from hydrogen-bonded linear polymers and helical coordination polymers, 2D sheets to 3D network architectures constructed via N–H⋯O, CO⋯H–Osolvent, O–H⋯O, N–H⋯OC hydrogen bonds and CO⋯π, C–H⋯π, and π⋯π stacking interactions. This review gives an account of the observed structural diversity in relation to the role of different donors and acceptors, aqua ligand and solvents, nature of the ligands and metal ions, coordination geometry around the metal ions and counter ions besides the experimental conditions such as temperature, pH, etc. in directing the formation of supramolecular structures in the solid state. Some other related and interesting examples from the literature are also mentioned.
One chiral heptanuclear FeIII cluster, {Fe[(FeL)2(μ2-OH)]3(μ2-OH)6}·13H2O (1) (H2L=N-(2-hydroxybenzyl)-l-histidine), has been synthesized and characterized structurally and magnetically. Complex 1 crystallizes in the chiral space group C2. The heptanuclear FeIII cluster of 1 has a propeller-like [Fe7(μ2-OH)9]12+ core, with the peripheral ligation provided by six tetradentate L2− ligands. The configurations of the C- and the N-centers of L2− is (S,R) and the central atom Fe4 is chiral Λ configuration. All FeIII centers are hexacoordinated, displaying a distorted octahedral coordination sphere. Variable temperature magnetic studies showed complex 1 is antiferromagnetic with C=14.27cm3Kmol−1 and θ=−27.56K. Magnetisation and susceptibility measurements show that cluster 1 exhibits a ground spin state of S=3.
The self-assembly of salicylaldehyde, d,l-aspartic acid and Cu(NO3)2·3H2O gave a 1D molecular ladder {[Cu2(sasp)2Cu(H2O)4]·0.5H2O}n (1) in which Cu(H2O)4 units serve as cross rungs and two sasp–Cu–sasp–Cu chains with opposite chirality serve as side rails. Compound 1 displays strong antiferromagnetic interactions within Cu3O2 trinuclear units and weak interunit ferromagnetic interactions. Interchain hydrogen bonds result in weak antiferromagnetic interactions.
Three new reduced amino-acid Schiff base complexes, [Co(HL)2(H2O)2] · 4H2O (1), [Cu(HL)2(H2O)2] · 2H2O (2), and [Cd(HL)2(H2O)3] · 2H2O (3), where H2L is the reduced Schiff-base ligand derived from the condensation of N-(4-hydroxybenzaldehyde) with L-glycine, have been synthesized and characterized by physico-chemical and spectroscopic methods.
In these complexes, the two bidentate monoanionic Schiff base ligands coordinate the metal center through the secondary amine
N atom and the carboxylate O atom. Water ligands complete a distorted octahedral (1, 2) or a pentagonal bipyramidal coordination geometry (3) around each metal center. The binding interactions of the complexes with CT-DNA have been investigated by UV–visible spectrophotometry
and fluorescence quenching methods. The results show that these complexes bind to CT-DNA with an intercalative mode. In addition,
DNA cleavage experiments have been also investigated by agarose gel electrophoresis. Complexes 1–3 show oxidative DNA cleavage activity in the presence of H2O2/sodium ascorbate and the reactive oxygen species responsible for the DNA cleavage is most likely singlet oxygen.
{[Cu2(L-val)2(4,4′-bipy)(H2O)2](NO3)2}n was synthesized and its crystal structure was determined by X-ray diffraction. In the presence of 4,4′-bipyridine, deprotoned L-valine chelates CuII ions into coordination layers which were linked into a framework by hydrogen-bonded chains resulting from nitrate anions and water molecules.
Three new reduced amino-acid Schiff-base complexes, [Zn(HL)2] · H2O (1), [Ni(HL)2] · H2O (2), and [Cd(HL)2] · H2O (3), where H2L is a reduced Schiff base derived from condensation of N-(2-hydroxybenzaldehyde) and L-histidine, have been synthesized and characterized by elemental analysis, UV-Vis absorption spectra and single crystal X-ray diffraction. Complexes 1–3 are isostructural. All metal centers are six-coordinate with O2N4 donor sets in slightly distorted octahedra. Unlike its Schiff-base counterpart, the deprotonated monoanionic ligand HL has a more flexible backbone and two HL are tridentate to one metal. Moreover, the binding interactions of these complexes with calf thymus DNA (CT-DNA) have been investigated by UV-Vis spectra and fluorescence quenching, which show that the complexes bind in an intercalative mode.
A new molecular capsule based on viologen–resorcinarene and sulfonatomethylene-resorcinarene is synthesized and its redox-controlled stability is investigated.
Four copper(II) complexes containing the reduced Schiff base ligands, namely, N-(2-hydroxybenzyl)-glycinamide (Hsglym) and N-(2-hydroxybenzyl)-l-alaninamide (Hsalam) have been synthesized and characterized. The crystal structures of [Cu2(sglym)2Cl2] (1), [Cu2(salam)2(NO3)2]·H2O (3), [Cu2(salam)2(NO3)(H2O)](NO3)·1.5H2O (4), [Cu2(salam)2](ClO4)2·2H2O (5) show that the Cu(II) atoms are bridged by two phenolato oxygen atoms in the dimers. The sglym ligand bonded to Cu(II) in facial manner while salam ligand prefers to bind to Cu(II) in meridonal geometry. Variable temperature magnetic studies of 3 showed it is antiferromagnetic. These Cu(II) complexes and [Cu2(sglym)2(NO3)2] (2), exhibit very small catecholase activity as compared to the corresponding complexes containing acid functional groups.
The redox chemistry and e.s.r. spectra of a number of copper(II) complexes with nitrogen- and sulphur-donor ligands have been examined, including complexes with 2,2′-bi-imidazole, histamine, and cyclic and acyclic saturated amine and thioether ligands. The tetrahedral CuIIS4 centre generated by γ-irradiation of single crystals of a thioacetamide complex of CuI has a low value of |A∥|. Tetrahedral distortion of otherwise tetragonal copper(II) centres increases g∥ and decreases |A∥| for N-, S-, and O-donor ligands, and is a more effective source of reduction of |A∥| than charge effects. The quotient g∥/|A∥| appears to be a convenient empirical index of distortion of the donor set from planar toward tetrahedral, indicating that most type I copper in proteins is tetrahedrally, rather than tetragonally, co-ordinated.
This article reviews recent progress in the study of the transition-metal mediated self-assembly of two- and three-dimensional synthetic receptors. Whereas macrocyclization under kinetic control is undoubtedly an unfavorable process, the self-assembly strategy offers quite efficient methods for constructing macrocycles under thermodynamic control. In particular, cis-protected Pd(II) and Pt(II) blocks are quite effective in obtaining the cyclic framework from simple molecules. Examples disclosed in this article are spontaneously assembled in quantitative yields by just mixing component molecules. This approach is successfully applied to the construction of cage compounds. The self-assembly of nanosized macrocycles and cages is also discussed.
The structure of monopyridinecopper(II) acetate has been determined by Patterson and Fourier syntheses from three-dimensional X-ray diffraction spectra. The copper atoms are bridged in pairs by four acetate groups to form binuclear molecules, Cu2(CH3·CO2) 4,2C5H5N, similar to those found in copper acetate monohydrate. The copper atom is 0.22 Å, out of the plane of the four oxygen atoms to which it is joined by covalent bonds (1.98 Å in length). The nitrogen atom of a pyridine molecule is attached to the copper atom by a slightly elongated covalent bond (2.13 Å long), giving the copper atom a distorted tetragonal-pyramidal co-ordination. The sixth, "octahedral," site is occupied by the second copper atom to which a δ-bond is formed (Cu-Cu distance 2.63 Aω). The binuclear molecule as a whole possesses a two-fold axis of symmetry which passes through the copper atoms and the pyridine molecules.
Louis Kahn, der Architekt des Salk Institute in La Jolla, sagte einmal:1 „Ein ganz gewöhnlicher, ordinärer Backstein möchte mehr sein als er ist“. Man stelle sich vor, das träfe auch auf Moleküle zu. Wir wissen, dass sie aggregieren können und es auch tun; sie bilden komplexe Strukturen und erhalten dabei neue Eigenschaften – Funktionen, die man bei der Untersuchung der einzelnen Komponenten nicht sieht. Dieser Aufsatz beschäftigt sich mit Molekülaggregaten einer ganz bestimmten Art, solchen, die andere Moleküle mehr oder weniger vollständig umschließen. Die beteiligten Moleküle erhalten dabei einzigartige Eigenschaften, und mit der Bildung des Aggregats als Ganzem entstehen neue Funktionen. Die Fähigkeit zur Aggregation – ein Ausdruck des Moleküls, dass es mehr sein möchte als es ist – resultiert aus dem gezielten Einbau von „Befehlen“ während der Synthese. Der Schwerpunkt soll auf der Beschreibung selbstkomplementärer Strukturen liegen.
Two pyridoxal (3-hydroxy-5-hydroxymethyl-2-methylpyridine-4-carbaldehyde) thiosemicarbazone (H2L) complexes of cobalt have been synthesised and structurally characterized by spectroscopic and X-ray diffraction methods. Crystallographic parameters: [Co(H0.5L)2]·3.5H2O 1 space group C2/c, a= 10.335(1), b= 29.026(3), c= 16.564(2)Å, β= 94.85(3)°, Z= 8, R= 0.053, R′= 0.057; [Co(HL)L]·4.5H2O 2, space group Pa= 11.195(1), b= 12.138(2), c= 11.128(1)Å, α= 103.23(3), β= 99.42(2), γ= 115.49(2)°, Z= 2, R= 0.058. In both compounds the cobalt atom is co-ordinated in a rather distorted octahedron to two molecules of pyridoxal thiosemicarbazone which are not equivalent. They are cobalt(III) complexes although the starting material was a cobalt(II) salt, differing in the H-atom positions of the pyridine nitrogen atoms. In 1 both the pyridine nitrogen atoms are ‘semiprotonated’: this is responsible for a loss of regularity in the arrangement of the water molecules. In 2 only one pyridine nitrogen atom is protonated. A. strong symmetric N H N hydrogen bond [2.685(9)Å] is present in complex 1.
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.
Experimental details are given for the preparation of large self-complementary molecules capable of assembly into pseudospherical capsules. These structures exist as hydrogen bonded dimers in organic solvents, and they form and dissipate on a time scale that permits direct NMR observation of the reversible encapsulation of smaller molecules. The cavity is roomy enough to accommodate more than one molecule, and two solvent molecules such as benzene appear to occupy the resting state of the capsules. Liberation of these solvent molecules is responsible for the unexpected thermodynamic parameters of the encapsulation process. A bimolecular reactionthe Diels−Alder reactionis shown to be accelerated by the capsule as both reactants can occupy the capsule concurrently. Size selectivity, saturation kinetics, and product inhibition studies point to a reaction that takes place within the capsule.
Crystal structures of a series of five symmetrically substituted N,N-bisarylformamidines ArNHCHNAr with Ar = X-C6H4, X = p-OCH3 (IV), p-CH3 (V), p-F (VI), p-NO2 (VII), and m-Br (VIII) have been determined by single-crystal X-ray diffraction (XRD) and complete the series studied previously where X = H (I), p-Br (II), and p-Cl (III). In addition, the results of variable-temperature 15N CPMAS NMR experiments performed on 15N-labeled I, II, and IV are reported. All compounds form cyclic dimers linked by two NH···N hydrogen bonds which can form two different tautomers, a and b, interconverting by fast double proton transfers. The NMR experiments indicate three types of amidines characterized by different magnitudes of the equilibrium constants Kab of the tautomerism. In dimers of type such as V−VIII, we find Kab 1 (i.e., only a single tautomer in the temperature range between 100 and 300 K). In this case, the hydrogen-bonded protons are ordered and can be localized by XRD. Furthermore, the C···N bond lengths and torsional and valence angles involving the two aryl groups of an amidine unit are different. For dimers such as II and III, characteristic temperature dependent 15N CPMAS NMR line shape changes are observed indicating that Kab = 1 within the margin of error. Rate constants of the tautomerism can in this case be obtained by line shape analysis. For this degeneracy to occur, the aryl group conformations at both amidine nitrogen atoms must be similar. XRD then observes disordered hydrogen-bond protons and, in principle, also disordered nitrogen atoms. However, in practice, the disorder of the latter is not resolved leading to the observation of equalized C···N bond lengths. Finally, dimers (I, IV) represent an intermediate case with Kab < 1, which could be labeled as “dynamic partial order”. The implications of the molecular structure and the hydrogen bond and proton transfer characteristics are discussed.
Four iron(II) ions help assemble a container molecule (1), by bringing together two hemispherical resorc[4]arenes. The resorc[4]arene ligands are appended with four iminodiacetate moieties which act as ligands for the iron atoms. X-ray crystallographic analysis of 1 shows that the iron atoms are coordinated in an N,N-cis-fac manner and exhibit a trigonal prismatic geometry. When 1 is formed in water, six water molecules, hydrogen bonded together, occupy its cavity. However, when 1 is formed with bromobenzene present in the water solution, bromobenzene is trapped in the cavity. Multinuclear NMR experiments (1H, 2H, and 19F) demonstrate the pH-dependent encapsulation of various organic guest molecules by 1, e.g., substituted benzenes, alkanes, ethers, and chlorocarbons. Complex 1 is the first iron(II)-containing cage complex that is formed by assembly of resorcinarene molecules and that binds neutral organic molecules.
A new resorc[4]arene ligand with four bis(pyridyl-methylamine) coordinating moieties (bpa-res) is described. The tetranuclear copper(II) complex of bpa-res shows that the bpa-res ligand serves as a template to assemble four copper atoms in close proximity to each other. The complex possesses four structurally unique copper(II) ions in the solid state, two of which form a discrete binuclear complex within the tetranuclear complex.
The crystal and molecular structure of [Cu(cyclops)py]ClO4 (1, cyclops = difluoro-3,3′-(trimethylenedinitrilo)bis(2-butanone oximato)borate, py = pyridine) has been determined from three-dimensional single-crystal X-ray diffraction data, collected by counter techniques. The purple crystals of 1 were orthorhombic, of space group P212121 (No. 19), with four formula units in the unit cell (a = 7.898 (5) Å, b = 14.040 (8) Å, c = 19.574 (11) Å). The structure of 1 was refined to R = 0.058 (Rw = 0.060) for 1361 independent reflections for which F2 > 3σ(F2). The discrete, monomeric complex ions of 1 exhibited a square-pyramidal coordination geometry about the copper(II) ion, with the pyridine ligand occupying the apical position and the four basal coordination sites being occupied by the nitrogen atoms of the quadridentate macrocyclic cyclops ligand. The displacement of the copper(II) ion from the basal plane of four coordinating nitrogen atoms is large (0.40 Å), despite the fact that the Cu(II)-N bonds remain strong (basal Cu-N(av) = 1.97 (1) Å). The observed degree of distortion of the metal ion coordination is achieved by a considerable degree of "flexing" of the macrocyclic ligand, which adopts a "chair"-like conformation, in contrast to that found in earlier copper(II) structures involving this macrocycle. In contrast to the complexes [Cu(cyclops)X] (X- = I-, NCO-) previously studied, where the bond to the anionic apical ligand was unprecedentedly strong, the Cu-N5(py) bond length of 2.170 (9) Å falls at the low end of the normal range for such bonds. This confirms the importance of both variations in the metal ion's apical displacement and the strength of the bond to the apical position in accounting for the spectroscopic properties of compounds in this series.
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Simple syntheses of the potentially tetradentate chelating ligands 6,6′-bis(3-pyrazolyl)-2,2′-bipyridine (H2L1), and 6,6′-bis(2-hydroxyphenyl)-2,2′-bipyridine (H2L2) are described: H2L1 is a new ligand, whereas H2L2 is known, but investigation of its coordination chemistry has been hampered by the lack of a simple synthesis. Complexes of both have been structurally characterised and reveal many interesting features. [Cu(HL1)(H2O)][PF6] is square pyramidal with an axial H2O ligand, but, in the solid state, forms a hydrogen-bonded dimer in which the peripheral pyrazolyl groups of HL1 (one protonated, one deprotonated) in one complex unit form a two-point ‘chelating’ hydrogen-bonding interaction with the axial water ligand of the second, and vice versa. In contrast, [Ag2(L1)2][BF4]2 is a dinuclear double helicate because of the preference of Ag(I) ions for a pseudo-tetrahedral geometry. [Cu(L2)] has a typical near-planar geometry with a N2O2 donor set, and monomeric units are associated into centrosymmetric dimers in the crystal via weak axial Cu⋯O(phenolate) interactions to give an asymmetric [Cu2(μ-phenolate)2] core. In {[Cu(L2)]2H}(PF6), the two monomeric [Cu(L2)] units are also associated via axial phenolate interactions to give a dimer with a [Cu2(μ-phenolate)2] core, but, in addition, the extra proton per dimer unit is located at the centre of a short, strong O⋯H⋯O hydrogen-bond that links a phenolate group from each of the two monomer units. The geometry of dimer formation is changed in order to allow the phenolate groups to approach one another closely enough for this hydrogen-bond to form.
The complex Co4 1(2)8- is a tetranuclear cobalt(II) cage compound that assembles in aqueous solutions above pH 4 and is capable of encapsulating a variety of organic guest molecules, for example, benzene, hexane, chlorobutane, butanol, and ethyl acetate. Ligand 1 is a resorc[4]arene-based molecule with iminodiacetate moieties appended to its upper rim. 1H NMR studies of Co4 1(2)8-.guest complexes demonstrate inclusion of nonpolar hydrocarbons, substituted phenyls, alcohols, halogen-containing hydrocarbons, and polar organic molecules. The complex Co4 1(2)8- acts as an NMR shift reagent and causes substantial upfield isotropic hydrogen shifts (-30 to -40 ppm) in the guest molecule and separation of the guest hydrogen chemical shifts by typically 12 ppm. The complex Co4 1(2)8- will encapsulate molecules with fewer than eight atoms in a linear chain, mono- and disubstituted benzenes, and polar molecules with greater than two carbon atoms. The solid-state structure of Ba4[Co4 1(2).C6H5C2H5] shows a disordered guest molecule encapsulated within the cavity of Co4 1(2)8-. The cavity dimensions, bond lengths, and bond angles of Ba4[Co4 1(2).C6H5C2H5] are very similar to those determined in Ba4[Co4 1(2).6H2O].
We provide a summary of our results in three-dimensional, coordination-driven self-assembly based on the directional-bonding methodology, in which the stoichiometric mixing of complementary building blocks, with appropriate, predefined geometries, leads to targeted, nanoscopic cages. Using this motif, we have synthesized high-symmetry ensembles resembling the Platonic solids, such as dodecahedra, and the Archimedean solids, such as truncated tetrahedra and cuboctahedra, as well as other cages, like trigonal bipyramids, adamantanoids, and trigonal prisms. The synthesis and characterization of these compounds is discussed, as is some host-guest chemistry.
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