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Coordination Frameworks Containing the Pyrimidin-4-olate Ligand. Synthesis, Thermal, Magnetic, and ab Initio XRPD Structural Characterization of Nickel and Zinc Derivatives
Abstract
Extended coordination frameworks containing the pyrimidin-4-olate ligand (4-pymo) and Zn(II) and Ni(II) metal ions have been obtained by solid state reactions and have been fully characterized by spectroscopic, thermal, and magnetic measurements and by ab initio XRPD. The reaction of ZnO and 4-Hpymo at 140 degrees C gives a solid microcrystalline phase, Zn(4-pymo)(2) (1). Its 3D framework contains Zn(II) centers linked by 4-pymo ligands acting in two different coordination modes, namely, the N,N'- and the N,O-exo-bidentate ones, which result in a pseudotetrahedral ZnN(3)O chromophore. Thermal treatment of the "molecular" Ni(4-pymo)(2)(H(2)O)(4) complex (2) above 140 degrees C gives an anhydrous amorphous material analyzing as Ni(4-pymo)(2) (3a). Further heating of this material above 388 degrees C results in the formation of the microcrystalline layered Ni(4-pymo)(2) species (3b), in which Ni(II) centers are bridged by N,O-exo-bidentate 4-pymo ligands (assisted by longer Ni.N contacts). The thermal dependence of the magnetic susceptibility has been studied for the paramagnetic species 2 and 3a. 2 shows a weak antiferromagnetic interaction [J = -0.313(5) cm(-)(1)] transmitted through the multiple H-bonding interactions between the exocyclic pyrimidine and water oxygen atoms coordinated to the metal centers. 3a behaves as a 2D Heisenberg antiferromagnet with J = -4.11(3) cm(-)(1).
... Comparative structural analysis involving the layered species: While less diffuse than the N,N'-exo-bidentate coordination mode, the N,O-exo-bidentate mode found in the gcompounds has been already exploited by both 4-and 2-pyrimidinolates: indeed, in the [{ZnA C H T U N G T R E N N U N G (4-pymo) 2 } n ] compound [22] and in the isomorphous [{M(5-NO 2 -2-pymo) 2 } n ] (M= Co, Zn) species, [12] the two crystallographically independent ligands concomitantly adopted these two coordination fashions. In the case of [{ZnA C H T U N G T R E N N U N G (4-pymo) 2 } n ], a three-dimensional topology was generated, while in the [{M(5-NO 2 -2-pymo) 2 } n ] materials the same two-dimensional topology as in g-Zn was present, with g-Zn being indeed isomorphous to them. ...
... In the case of [{ZnA C H T U N G T R E N N U N G (4-pymo) 2 } n ], a three-dimensional topology was generated, while in the [{M(5-NO 2 -2-pymo) 2 } n ] materials the same two-dimensional topology as in g-Zn was present, with g-Zn being indeed isomorphous to them. While the b and c cell parameters of these three isostructural species are highly comparable (9.6084(5), 9.3685(5) for g-Zn [23] and Ni [22] ); in this case, the metal centres were strictly coplanar and, above all, the less common N,O-coordination mode was the only type of ligand bridging, even if supported by ancillary M···N long interactions. ...
The novel porous [{M(F-pymo)(2)}(n)]2.5n H(2)O coordination networks (M=Co, Zn; F-pymo=5-fluoropyrimidin-2-olate), possessing sodalitic topology, have been synthesised and structurally characterised by means of powder diffraction methods. Thermodiffractometry demonstrated their plasticity: when heated up to 363 K, they reversibly transform into three-dimensional dehydrated [{M(F-pymo)(2)}(n)] species, with significantly different lattice parameters. Further heating induces irreversible polymorphic transformations into layered phases, in which the original MN(4) coordination sphere changes into an MN(3)O one. A mixed-metal phase, [{Co(x)Zn(1-x)(F-pymo)(2)}(n)]2.5n H(2)O, was also prepared, showing that zinc is preferentially inserted, when starting from a Co/Zn reagent ratio of 1:1. The solid-gas adsorption properties of the anhydrous 3D frameworks have been explored towards N(2), H(2) (77 K) and CH(4), CO(2) (273 K). These results show that these materials permit the diffusion of CO(2) molecules only. Remarkably, the CO(2) adsorption process for the [{Co(F-pymo)(2)}(n)] network proceeds in two steps: the first step takes place at low pressures (<600 kPa) and the second one above a threshold pressure of 600 kPa. By contrast, the [{Zn(F-pymo)(2)}(n)] network only permits CO(2) diffusion by applying pressures above 900 kPa. This type of behaviour is typical of porous networks with gated channels. The high CO(2) selectivity of these systems over the rest of the essayed probe gases is explained in terms of flexibility and polarity of the porous network. Finally, the magnetic studies on the Co(II) systems reveal that the as synthesised [{Co(F-pymo)(2)}(n)]2.5n H(2)O material behaves as an antiferromagnet with a T(N) of about 29 K. At variance, the [{Co(F-pymo)(2)}(n)] layered phase shows an unusually weak ferromagnetic ordering below 17 K, arising from a spin-canting phenomenon.
... The complexes with exclusively hydrogen bonded Ni(II) ions, analyzed beyond the Curie-Weiss law, are listed in Table 7 (Refs. [45][46][47][48][49][50][51][52]). ...
Metal-organic frameworks represent the ultimate chemical platform on which to develop a new generation of designer magnets. In contrast to the inorganic solids that have dominated permanent magnet technology for decades, metal-organic frameworks offer numerous advantages, most notably the nearly infinite chemical space through which to synthesize predesigned and tunable structures with controllable properties. Moreover, the presence of a rigid, crystalline structure based on organic linkers enables the potential for permanent porosity and postsynthetic chemical modification of the inorganic and organic components. Despite these attributes, the realization of metal-organic magnets with high ordering temperatures represents a formidable challenge, owing largely to the typically weak magnetic exchange coupling mediated through organic linkers. Nevertheless, recent years have seen a number of exciting advances involving frameworks based on a wide range of metal ions and organic linkers. This review provides a survey of structurally characterized metal-organic frameworks that have been shown to exhibit magnetic order. Section 1 outlines the need for new magnets and the potential role of metal-organic frameworks toward that end, and it briefly introduces the classes of magnets and the experimental methods used to characterize them. Section 2 describes early milestones and key advances in metal-organic magnet research that laid the foundation for structurally characterized metal-organic framework magnets. Sections 3 and 4 then outline the literature of metal-organic framework magnets based on diamagnetic and radical organic linkers, respectively. Finally, Section 5 concludes with some potential strategies for increasing the ordering temperatures of metal-organic framework magnets while maintaining structural integrity and additional function.
Luminescent [Cu2I2(pyrpy)2(PR3)2] complexes (pyrpy = 4-pyrrolidinopyridine; PR3 = triphenylphosphine (1), tri- m-tolylphosphine (2), tri- p-tolylphosphine (3)) were prepared by solution reactions and a rarely reported solvent-free thermal method. X-ray structure analyses reveal that complexes composed of dinuclear {Cu2I2} cores surrounded by two PR3 and two pyrpy ligands were formed. Although the melting point of pyrpy is the lowest among the organic units used in this study, the temperature required to form the luminescent dinuclear complex, prepared by the thermal synthesis method, depended strongly on the PR3 moiety. Two of the three complexes (1 and 3) were successfully prepared by the solvent-free thermal method. Complexes 1-3 exhibited blue emissions at around 450 nm with moderately high quantum yields (Φ) of 0.24, 0.31, and 0.51, respectively. Emission-lifetime measurements and time-dependent density functional theory (TD-DFT) calculations suggest thermally activated delayed fluorescence (TADF) in each complex. This solvent-free thermal synthesis of TADF materials represents a promising method for the preparation of luminescent layers directly onto substrates of thin-layer electronic devices, such as organic light-emitting diodes.
In situ formation of ligands is an efficient approach to synthesizing novel complexes with unique coordinating moieties. Oxazolidines and oxazinanes are 1,3-N,O-containing five-membered and six-membered heterocycles, respectively. Metal complexes of ligands derived from these two heterocycles are rather rare. In this work, we designed and synthesized a novel multihydoxy ligand, 2-((2,3-dihydroxypropylamino)methyl)phenol (H3L1). It contains both aminoethanol and aminopropanol units, which may be employed to react with aldehydes to afford oxazolidines and oxazinanes, respectively. Thus, H3L1 was reacted with metal salts in the absence or presence of aldehydes to afford complexes [Cu(HL1)]2 (1), [CuL2]4·4CH3OH (2) [Zn5Na2(L3)4(DMSO)2.65(DMF)1.35]·DMF (3), and [Ni(HL4)]2 (4). Complex 1 is a dialkoxo-bridged binuclear Cu(II) complex. The coordination moieties are linked by intermolecular C–H···O hydrogen bonds to afford a 1D double-chain supramolecular structure. Interestingly, in complexes 2–4, H3L1 has been reacted with formaldehyde, salicylaldehyde, and 2,6-diformyl-4-cresol to afford novel ligands H2L2, H3L3, and H3L4, respectively. The combination of in situ formed oxazinane or oxazolidine rings with appended alkoxyl and phenol functionalities in these ligands has been demonstrated to form a rich diversity of coordination structures. Thus, 2 is a tetranuclear Cu(II) complex with a face-sharing double defective cubane core structure. In this complex, (L2)2– ligands coordinate in two different bridging modes with the Harris notations of 3.1121221311 and 3.1131231111, respectively. Complex 3 has an interesting heptanuclear Zn5Na2 core structure. A central Zn(II) is coordinated with four alkoxo O atoms from four (L3)3– ligands. Each of the O atom further bridges another Zn(II) atom, resulting in a Zn5 moiety, which is then connected to two Na+ by phenoxo O bridges, finally affording the Zn5Na2 core. The bridging mode of (L3)3– can be designated as 4.21221311312411. And Complex 4 is a binuclear Ni(II) complex containing di-μ2-phenoxo bridges. The coordination moieties are linked by intermolecular C–H···π, C–H···O, and π···π interactions to afford a two-dimensional supramolecular network. These results indicate that the combination of in situ formed oxazinane and oxazolidine rings with appended phenol and alkoxyl functionalities is an efficient approach to developing novel ligands and complexes with a rich structural diversity. Variable temperature magnetic data measurements revealed that medium antiferromagnetic interaction exists between the Cu(II) centers in complex 1 with a −2J value of 278 cm–1. And in complex 4, weak antiferromagnetic coupling occurs between the Ni(II) centers, with a −2J value of 9.36 cm–1.
Polymeric metal diazolates typically appear as insoluble and intractable powders, the structure of which could only be retrieved by the extensive use of ab-initio X-ray powder diffraction (XRPD) methods from conventional laboratory data. A number of selected examples from the metal pyrazolate, imidazolate, pyrimidin-2-olate and pyrimidin-4-olate classes are presented, highlighting the specific crystallochemical properties, material functionality and methodological aspects of the structure determination process. Linear and helical one-dimensional polymers, layered systems and three-dimensional networks are described, with particular emphasis on polymorphism and on the thermal, optical, magnetic and sorption properties. A brief outline of the method, as it has been tailored in our laboratories during the last decade, is also offered.
When the polymeric complex [Ag(im)]n (Him = imidazole) is reacted with PPh3 (PPh3 = triphenylphosphine), it yields the [Ag2(μ2-im)2(PPh3)3]n and [Ag(μ2-im)(PPh3)2]n species, shown to contain wavy chains of metal ions, singly bridged by N,N′-exo-bidentate imidazolate ligands. The former, crystallised as the CH2Cl2 solvate, contains two non-equivalent silver(I) ions, differing in the number of coordinated phosphines (one, in trigonal planar stereochemistry, or two, having tetrahedral geometry). The latter has a unique independent silver(I) ion in a tetrahedral environment, with two coordinated PPh3 ligands. The reactivity of known silver(I) azolates with PPh3, as well as the solution behaviour and (when available) the crystal structures of the corresponding derivatives are taken into consideration for a due comparison.
This article focuses on heating or annealing process in the mechanochemical preparation of coordination compounds in the solid state. Heating of metal complexes often promotes the liberation of weakly coordinated ligands and results in the complex with its coordination geometry unsaturated. Such “activated” complexes can be used as the building blocks of coordination polymers in the solid state. As one example, our recent work on [M(CNacac)2]∞ (CNacac = 3-cyano-pentane-2,4-dionato, M = MnII, FeII, CoII, NiII, CuII and ZnII) is presented. Further, co-grinding and annealing treatments of an enantiomeric pair of chiral crystals of [M(phen)3](PF6)2 (M = RuII and OsII, phen = 1,10-phenanthoroline) afford diffusion and rearrangement of transition metal complex ions to form co-crystal phases of racemic or quasi-racemic compounds by way of recognizing chirality. Our latest result of co-crystal formation via chirality transfer between optically stable and labile metal complexes is also briefly introduced.
The use of X-ray powder diffraction for the structure determination of inorganic, organic and metal-organic compounds has grown impressively over the last ten years. In supramolecular chemistry, the knowledge of the three-dimensional structure of a material is essential for the discussion of its macroscopic behaviour, and as a result the design of new functionalized materials.
The
The reaction of pyrazine-2,5-dimethyl-3,6-dicarboxylic acid with first row transition metal salts lead to the formation of coordination polymers always in the form of microcrystalline powders. With manganese and nickel salts isostructural 1D coordination polymers were obtained. With zinc chloride and copper chloride isomorphous 1D coordination polymers were obtained. The thermal decomposition of the nickel and copper polymers were studied and it was shown that on the loss of the coordinated water molecules new 3D coordination polymers could be obtained. In both the 1D and 3D coordination polymers the metal atoms have octahedral geometry in N
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.
The complex 2{[Ni(l-Tyr)2(bpy)]}·3H2O·CH3OH [1, where l-Tyr = l-tyrosine; bpy = 2,2'-bipyridine (2,2'-bpy)] was obtained in crystalline form and characterized by X-ray and spectroscopic (FT-IR, NIR-vis-UV, and HFEPR) and magnetic methods. The complex crystallized in the hexagonal system with a = b = 12.8116(18) Å, c = 30.035(6) Å, and space group P3221. The six-coordination sphere around the Ni(2+) ion is formed by two N and two O l-tyrosinato atoms and completed by two N atoms of the 2,2'-bpy molecule. Neighboring [Ni(l-Tyr)2(bpy)] units are joined via weak hydrogen bonds, which create a helical polymeric chain. The coordinated atoms form a strongly distorted cis-NiN2N2'O2 octahedral chromophore. The solid-state electronic spectrum of complex 1 was analyzed assuming D2h symmetry, and the observed bands were assigned to (3)B1g → (3)Ag, (3)B1g → (3)B3g, (3)B1g → (3)B2g, (3)B1g → (3)B3g, (3)B1g → (3)B1g, and (3)B1g → (3)B2g transitions for the I and II d-d bands, respectively. The crystal-field parameters found for D2h symmetry are Dq = 1066 cm(-1), Ds = 617 cm(-1), Dt = -93 cm(-1), B22 = 7000 cm(-1), and Racah B = 812 cm(-1). Magnetic studies revealed the occurrence of hydrogen-bonded metal pairs. The spin Hamiltonian parameters D = -3.262 cm(-1) and E = -0.1094 cm(-1), determined from high-field, high-frequency electron paramagnetic resonance spectra, together with a weak antiferromagnetic exchange parameter J = -0.477 cm(-1), allowed us to reproduce the powder magnetic susceptibility and field-dependent magnetization of the complex. The biological activity of 1 has been tested by using the Fusarium solani, Penicillium verrucosum, and Aspergillus flavus fungi strains and Escherichia coli, Pseudomonas fluorescens, Serratia marcescens, and Bacillus subtilis bacterial strains.
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.
This chapter reviews the syntheses and reactions of 6-membered heterocyclic ring systems, such as diazines and benzo derivatives. The diazines pyridazine, pyrimidine, pyrazine, and their benzo derivatives, cinnoline, phthalazine, quinazoline, quinoxaline, and phenazine, played a central role in many investigations. Progress has been made on the syntheses and reactions of these heterocycles and their use as intermediates toward broader goals. Some studies relied on solid-phase, microwave irradiation, or metal-assisted synthetic approaches, while others focused attention more on the X-ray, computational, spectroscopic, and natural product and other biological aspects of these heterocycles. Hydrohydrazinations are widely used in the preparation of pyridazines. One-pot N-alkylations and hydrazinations give 5-alkyl-2,5-dihydro-1H-pyridazino[4,5-b]indol-1-ones and -1,4(5H)-diones. 6-substituted 5-hydroxy-3-oxo-2,3-dihydropyridazine-4-carboxylates are prepared in good yields via an intramolecular Dieckmann cyclization. The synthesis of pyridazines functionalized with amino acid moieties proceeds simply via a Tebbe olefination followed by a Diels–Alder reaction with tetrazine.
Reactions between the tritopic pyrazole-based ligand 1,3,5-tris(1H-pyrazol-4-yl)benzene (H 3 BTP) and transition metal acetate salts in DMF afford microporous pyrazolate-bridged metal–organic frameworks of the type M 3 (BTP) 2 $xsolvent (M ¼ Ni (1), Cu, (2), Zn (3), Co (4)). Ab-initio X-ray powder diffraction methods were employed in determining the crystal structures of these compounds, revealing 1 and 2 to exhibit an expanded sodalite-like framework with accessible metal cation sites, while 3 and 4 possess tetragonal frameworks with hydrophobic surfaces and narrower channel diameters. Compounds 1–4 can be desolvated without loss of crystallinity by heating under dynamic vacuum, giving rise to microporous solids with BET surface areas of 1650, 1860, 930 and 1027 m 2 g À1 , respectively. Thermogravimetric analyses and powder X-ray diffraction measurements demonstrate the exceptional thermal and chemical stability of these frameworks. In particular, 3 is stable to heating in air up to at least 510 C, while 1 is stable to heating in air to 430 C, as well as to treatment with boiling aqueous solutions of pH 2 to 14 for two weeks. Unexpectedly, 2 and 3 are converted into new crystalline metal–organic frameworks upon heating in boiling water. With the combination of stability under extreme conditions, high surface area, and exposed metal sites, it is anticipated that 1 may open the way to testing metal–organic frameworks for catalytic processes that currently employ zeolites.
In this chapter, we give an overview of the recent state-of-the-art research of porous and magnetic molecule-based materials. The subject is introduced by a section devoted to the fundamentals of magnetism in molecular magnets, with special attention to the design strategies to prepare molecular magnetic materials. We will then focus on the two main families of materials combining porosity and magnetism: the purely organic and the metal-organic porous magnetic materials. For both families, a selection of the most representative examples has been made. A complete section is devoted to magnetic and porous materials with flexible frameworks, an area of emerging importance in this field, because of their wide range of applications. Finally, we conclude with a brief overview on the most recent approaches for the future development of these materials.
The preparation, characterization, and optimization of the functional properties of mono- and polynuclear coordination complexes containing heteroaromatic nitrogen ligands are discussed here, taking the advantage of numerous studies performed in our laboratories on exploring a variety of different metal ions and polytopic ligands. We highlight how very minor changes in connectivity, composition, and polarity of the molecular entities employed in the self-assembly steps may significantly affect the structural, thermal, sorptive, magnetic, and mesomorphic behavior of the resulting materials. Examples from three different classes are included: 1) pyrazolate-based polynuclear coordination compounds, 2) homoleptic and heteroleptic coordination polymers, and 3) 2,2'-bipyridine metal-based liquid crystals.
In searching for coordination polymers containing the highly polarized 5-nitro-pyrimidin-2-olate ligand (NP), a number of species containing 3d transition metals have been prepared and characterized, namely Co(NP)2(H2O)4, [Co(NP)2]n, Ni(NP)2(H2O)4, [Ni(NP)2]x, and [Zn(NP)2]n. Their structures have been determined by X-ray powder diffraction methods. The hydrated compounds contain mononuclear M(NP)2(H2O)4 units interconnected by means of a three-dimensional (3D) network of hydrogen bonds. The homoleptic species, at variance from the already known metal(II) pyrimidin-2-olate ones, crystallize as two-dimensional (2D) slabs, where the metal coordination is of the MN3O kind. The electron-withdrawing nitro group, never bound to the metal ion, is likely to influence the observed stereochemistry through steric and dipolar effects within the crystal lattice. The thermal, spectroscopic, and magnetic properties of these species are presented. The M(NP)2(H2O)4/[M(NP)2]x,n systems interconvert reversibly upon dehydration/rehydration processes.
Two novel metal-organic frameworks (MOFs)--[Mn(titmb)(N3)2] x 1.5H2O (1) and [Mn3(titmb)2(C2O4)3(H2O)] x 10H2O (2)--were obtained by reactions of the flexible tripodal ligand 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (titmb) with Mn(OAc)2 x 4H2O, together with NaN3 and K2C2O4, respectively. The structures of these MOFs were established by single-crystal X-ray diffraction analysis. The crystal data for 1 were as follows: monoclinic, C2/c, a = 20.956(13) A, b = 9.884(6) A, c = 24.318(14) A, beta = 95.87(5) degrees, Z = 8. The crystal data for 2 were as follows: triclinic, P1, a = 12.400(9) A, b = 16.827(12) A, c = 17.196(11) A, alpha = 66.35(5), beta = 95.87(5) degrees, gamma = 71.03(6), Z = 2. Complex 1 is a novel noninterpenetrating three-dimensional (3D) framework, in which the azide ligand connects Mn(II) atoms in an end-to-end (EE) mode to give [Mn-N-N-N-]n infinite one-dimensional (1D) chains, and complex 2 has a two-dimensional (2D) network structure in which the Mn(II) ions are linked by the oxalate anions to form 1D [Mn(C2O4)]n chains. Each titmb in these two complexes connects three metal atoms and serves as a three-connecting ligand. The magnetic properties of 1 and 2 were investigated. The results showed that the antiferromagnetic interactions occurred between the Mn(II) ions linked by the azide ligands in complex 1, and those linked by the oxalate anions and the carboxylate in syn-anti coordination mode in complex 2. The entirely different structures of complexes 1 and 2, on one hand, indicate that the azide and the oxalate ligands affected the structures of MOFs greatly, and on the other hand, reveals the potential applications of MOFs with the azide and oxalate ligands, which are efficient magnetic couplers.
A solvothermal synthetic procedure has been exploited to prepare the new [Cu(3)L(NO(3))(6)](n) coordination polymer (1) by reaction of the polydentate N,N'-{2,4-di-[(di-pyridin-2-yl)amine]-1,3,5-triazine}ethylenediamine ligand (opytrizediam L) with copper(II) nitrate. 1 has been structurally characterized by means of the conventional X-ray single-crystal diffraction technique. It crystallizes in the monoclinic C2/c space group with a = 16.830(3), b = 20.701(4), c = 18.170(4) Angstroms, beta = 113.26(3) degrees, V = 5816(2) Angstroms(3), Z = 4. 1 consists of trinuclear Cu(3)L(NO(3))(5) units connected by means of a nitrato-O,O' bridge. The resulting chains are involved in weak interchain head-to-tail pi-pi stacking interactions. In the presence of moisture, 1 is readily converted into the hydrated [Cu(3)L(NO(3))(5)](NO(3)).H(2)O form (2). This second phase, monoclinic P2(1)/c, consists of isolated [Cu(3)L(NO(3))(5)](+) and (NO(3))(-) ions which accommodate water molecules in the crystal lattice. These subtle chemical and structural modifications accompanying the moisture-triggered 1-to-2 transformation have been demonstrated through a X-ray powder diffraction study. A thermodiffractometric analysis has evidenced that this solid-to-solid transformation is fully reversible, i.e., thermally induced dehydration of 2 restores 1. The analysis of the temperature dependence of the magnetic susceptibility for 2 has revealed very weak ferromagnetic interactions, consistent with the large Cu...Cu separation (ca. 7.5 Angstroms) in the trinuclear units.
The mixed ligand complex [Ni(CMA)2(im)2(MeOH)2] (where CMA = 9,10-dihydro-9-oxo-10-acridineacetate ion, im = imidazole) was prepared, and its crystal and molecular structure were determined. The nickel ions are hexa-coordinated by four oxygen atoms of the carboxylate and hydroxyl groups and by two imidazole nitrogen atoms, to form a distorted octahedral arrangement. The structure consists of a one-dimensional network of the complex molecules connected by strong intermolecular hydrogen bonds. The weak intermolecular C-H...X hydrogen bonds and stacking interactions make up the 2-D structure. Very strong intramolecular hydrogen bonds significantly affect the geometry and vibrational characteristics of the carboxylate group. The UV-vis-NIR electronic spectrum was deconvoluted into Gaussian components. Electronic bands of the Ni(II) ion were assigned to suitable spin-allowed transitions in the D4h symmetry environment. The single ion zero-field splitting (ZFS) parameters for the S = 1 state of Ni(II), as well as the g components, have been determined by high-field and high-frequency EPR (HF-HFEPR) spectroscopy over the frequency range of 52-432 GHz and with the magnetic fields up to 14.5 T: D = 5.77(1) cm-1, E = 1.636(2) cm-1, gx = 2.29(1), gy = 2.18(1), and gz = 2.13(1). These values allowed us to simulate the powder magnetic susceptibility and field-dependent magnetization of the complex.
The bimetallic complex [CoNi(pmzt)4] (pmtz- = 5-(pyrimidyl)tetrazolate ligand) has been prepared by hydrothermal treatment of an equimolecular mixture of the mononuclear complexes[Co(pmtz)2(H2O)2] and [Ni(pmtz)2(H2O)2]. The structure of [CoNi(pmzt)4] consists of (4,4) square-grid-like sheets, in which Co(II) and Ni(II) metal ions are connected by pmtz(-) bridging ligands. This compound is a spin-canted antiferromagnet (weak ferromagnet) with Tc = 18 K. Although Co(II) and Ni(II) ions have different spin values, the spin-canted structure can be formed because of the accidental compensation of their magnetic moments. Both magnetic anisotropy and antisymmetric exchange interaction promote the spin canting of the compensated magnetic moments in the 3D antiferromagnetic phase. On passing from the homometallic complex, [Co2(pmzt)4], which is also a spin-canted antiferromagnet with Tc = 15 K, to the bimetallic complex, [CoNi(pmzt)4], Tc increases and the hysteresis parameters, remnant magnetization (Mr) and critical field (Hc), decrease. The increase in Tc may be a consequence of the increase of the JCoNi, whereas the decrease in Mr and Hc is probably due to the presence in [CoNi(pmzt)4] of a lower content of the highly anisotropic Co(II) ion.
An indexing program, TREOR, mainly based on trial-and-error methods is described. The program contains separate routines for cubic, tetragonal, hexagonal, orthorhombic, monoclinic and triclinic symmetries. Ten years usage has been analysed to improve the original program. For monoclinic indexing a specific short-axis test has been developed. The over-all success rate of the program has been found to be better than 90%, and considerably more for orthorhombic and higher symmetries.
Complexes of 4,5,6,7-tetrahydro-5,7-dioxo- , and triazolo- and pyrimidine (H2tpO2) with the divalent transition metals of the first transition series from Mn to Zn have been synthesized and characterized, their general formula being M (HtpO2) 2 · nH2O. The crystal structure of the manganese compound, [Mn (HtpO2) 2 (H2O) 2] , has been solved by single crystal X-ray diffraction, showing that the ligand binds bidentately through the exocyclic oxygen O7 and the endocyclic nitrogen N1. The deprotonation of the ligand takes place at the active methylene group at position 6, as it happened in Na (HtpO2) · 2H2O, and not at the N — H group at position 4. Infrared data suggest that the ligand binds in a similar fashion in the Fe, Co, Ni and Zn compounds but not in the copper one. This has been corroborated by powder X-ray diffraction, which indicates that all compounds except Cu are isostructural.
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.
The first six coefficients in the expansion of the susceptibility chi, and its inverse, chi-1, in ascending powers of the reciprocal temperature, have been determined for the Heisenberg model of a ferromagnetic, for any spin value, S, and any lattice. The first five coefficients appropriate to the magnetic specific heat, C, have also been found. For the body-centred and face-centred cubic lattices, the chi and C coefficients are tabulated for half-integral S from 1/2 to 3. From these coefficients estimates have been made of the reduced Curie temperatures, thetasc=kTc/J. It is found that for the simple, body-centred and face-centred cubic lattices the formula tMPH0257_images reproduces the estimated Curie temperatures fairly accurately. Here X=S(S+1) and z is the lattice coordination-number. It is found that, suitably scaled, the theoretical curves for inverse susceptibility against temperature above the Curie point are rather insensitive to the spin value and to the precise lattice structure. The ratio of their initial to their final gradients is approximately 0·3. A comparison is made with the experimental values of chi-1 for both iron and nickel. If iron is represented by the Heisenberg model with S=1, then the observed Curie temperature corresponds to a J value of 1·19×10-2 ev. Brief consideration is given to the use of the tabulated coefficients for antiferromagnetic problems.
The identification of twofold axes is straightforward if the cell is based on three of the shortest lattice translations. The distribution of twofold axes in space fixes the lattice symmetry and most conventional cell edges. A program based on this approach has been written. It works for the seven cases with minimum branching of the algorithm.
At present, over 30 000 powder diffraction patterns are available as references. It is proposed that the patterns on file as well as new patterns submitted for publication be assigned quantitative quality factors. A simple-to-use figure of merit, FN, covering both accuracy in the measurement of the positions of the diffraction lines and completeness of the pattern, has been derived: FN = (1/||) (N/Nposs), where Nposs is the number of independent diffraction lines possible up to the Nth observed line and || is the average absolute discrepancy between observed and calculated 2θ values. This figure of merit provides a rapid evaluation of powder patterns, in much the same way as the R factor provides a rating for single-crystal structure determinations. This figure of merit also provides a means to assess the reliability of a unit derived solely from powder data. At present FN ranking scheme is shown to be superior to de Wolff's M20 for ranking patterns. It is recommended that use of the latter be discontinued for that purpose. Guidelines are given on the use and implementation of the FN rating of powder diffraction patterns.
The application of supramolecular concepts such as self-assembly to the solid state offers an approach to crystal design and crystal engineering, namely supramolecular synthesis of solids, that is based upon the design of infinite networks. Self-assembly of more than one molecular component, modular self-assembly, is particularly attractive since it can be accomplished in one-pot reactions with existing molecular components and allows for facile fine-tuning of structural and functional features. The challenges and opportunities that face crystal engineering are illustrated by concentrating on the superstructural diversity that has been exhibited in 2D network structures. Despite the observed superstructural diversity, which can manifest itself in the form of supramolecular isomerism, and the range of molecular components that have been utilized, these structures have in common an inherent ability to mimic clays by intercalation of guest molecules.
The electronic ligand field spectra of high-spin species of cubic symmetry with d2,d3,d7,d8 ions consist in general of three bands that arise from three spin-allowed transitions.
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.
The reaction of zinc() bromide with pyrazine yielded the two coordination polymers (ZnBr2(pyz)) 1 and (ZnBr2(pyz)2) 2. Crystal structures of these two compounds show that 1 is a 1-D zigzag chain polymer while 2 forms a regular square-grid (4,4) network. Adjacent grids in 2 are slipped in one direction so that the axial bromide ions on one layer project into the cavities of the grids in adjacent layers. The solid-state reaction of 1 with pyrazine yields 2, and 2 in its turn is readily converted into 1 by heating. The activation energy of the latter process has been determined as 99.8 kJ mol 1 .
A figure of merit is defined for an indexing of a given pattern as M20 = Q20/2N20. Here N20 is the number of different calculated Q values up to Q20, which is the Q value for the 20th observed and indexed line; is the average discrepancy in Q for these 20 lines. From a number of indexings which have been disproved by single-crystal analysis, the conclusion is drawn that M20 < 6 must give rise to considerable doubt about the result. A number of confirmed indexings shows values of 20–60 for good routine work on pure, well crystallized samples, and down to 6 for retrievable correct indexings of less accurate data. If the number of unindexed lines below Q20 is not more than two, a value M20 > 10 guarantees that the indexing is substantially correct.
Ab-initio X-ray powder diffraction (see cover for typical spectra) is shown to be a powerful structural tool for (i) insoluble, thermally unstable, compounds which cannot be (re)crystallised from solution or from the melt; (ii) metastable phases destroyed or modified upon manipulation; (iii) twins; (iv) very small crystals and/or crystal aggregates; (v) gas/solid, liquid/solid and solid-state reactions fragmenting and misorienting the coherent domains of the starting crystals but conserving the (poly)crystalline nature of the sample.
Bis(1,1,1-trifluoro-5,5-dimethyl-5-methoxy-acetylacetonato)copper(II) was prepared in two polymorphic modifications. The orthorhombic α-form is stable and densely packed, with four trans and four cis square bischelate building blocks per unit cell. These are connected through additional coordination bonds to form a dense polymer network. For the trigonal β-form, the square bischelate complex units are present exclusively as the trans isomers. The distinctive assembly of these units results in a lattice with an open pore volume of about 17% that is accessible to a wide range of guests. The compound has a remarkably strong affinity for the porous β-form as evident from the efficient α-to-β conversion on contact not only with liquid guests but also with organic vapors at pressures well below the saturation pressure. Although the open β-form is metastable, it has a remarkable kinetic stability, most likely because of the trans-to-cis isomerization that must accompany the β-to-α transformation. Many sorbents play a dual role as stabilizing guest and as catalyst promoting the α-to-β or β-to-α conversion. Because of its versatile sorption properties and relative robustness, the β-form of the complex can be classified as a novel organic zeolite mimic.
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.
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.
Acentric three-dimensional coordination polymers bis(isonicotinato)zinc (1) and bis(4-pyridylacrylato)cadmiumH2O (2) were synthesized under hydro(solvo)thermal conditions; they exhibit a threefold (see picture) and fivefold diamondoid structure, respectively. Both 1 and 2 are active for second harmonic generation and exhibit remarkable thermal stability.
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.
Changing channels! The crystal-to-crystal sliding of a 2D network between two packing modes is triggered by the guest exchange of solvent molecules, and results in considerable difference in the channel dimensions (a → b; see scheme).
This paper discusses the statistical mechanics of the isotropic and the weakly anisotropic quadratic-layer antiferromagnet. This system is of current interest since it appears to be quite a good model for the less anisotropic members of two recently discovered isomorphic series of antiferromagnetic layer crystals. The antiferromagnetic phase, depending for its very existence on anisotropy, is discussed using spin-wave and Green's function methods, and comparisons are made with a typical three-dimensional (simple-cubic) system. The paramagnetic phase is investigated by Green's function and high temperature series expansion techniques, with particular attention paid to magnetic susceptibility and spin correlations. By expanding the Green's function results as a high temperature series, a test of the extrapolation techniques, which are frequently used in conjunction with this type of series and are particularly controversial for the two-dimensional Heisenberg system, can be made in the Green's function context.
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.
Techniques and methods to facilitate the solution of structures by simulated annealing have been developed from the starting point of a space group and lattice parameters. The simulated-annealing control parameters have been systematically investigated and optimum values characterized and determined. Most significant is the inclusion of electrostatic-potential penalty functions in a non-linear least-squares Rietveld refinement procedure. The long-range electrostatic potentials are calculated using a general real-space summation which can be used for all space groups. In addition, a general weighting scheme for penalty functions negates the need to determine weighting schemes experimentally. Also investigated and improved is the non-linear least-squares minimization procedure used in the refinement of structural parameters. The behaviour and success of the techniques have been tested on X-ray diffraction powder data against the known structures of AlVO4 in P1 with 18 atoms in the asymmetric unit, K2HCr2AsO10 in P31 with 15 atoms in the asymmetric unit excluding hydrogen, and [Co(NH3)5CO3]NO3.H2O in P121 with 15 atoms in the asymmetric unit excluding hydrogen.
A convolution approach to X-ray powder line-profile fitting is developed in which the line shape is synthesized from the Cu K-alpha emission profile, the dimensions of the diffractometer and the physical variables of the specimen. In addition to the integrated intensities and 2-theta positions of the line profiles, the parameters that may be fitted include the receiving-slit width, the receiving-slit length, the X-ray-source size, the angle of divergence of the incident beam, the X-ray attenuation coefficient of the specimen and the crystallite size. This is a self-consistent approach to fitting as the instrumental parameters are usually known by direct measurement. To minimize correlation between refined instrumental parameters, profiles at high and low 2-theta values should be fitted simultaneously. The Cu K-alpha emission profile used in this work is based on recent monolithic double-crystal spectrometer measurements that have identified a doublet structure in both the K-alpha-1 and K-alpha-2 components. Fast and accurate convolution procedures have been developed and a mixture of multilinear regression and Gauss-Newton non-linear least squares with numerical differentials is used for fitting the profiles. The method is evaluated by fitting powder diffraction data from well crystallized specimens of MgO and Y3Al5O12 (YAG). Testing has also been carried out by examining the changes in the fitted values after altering various instrumental parameters (e.g. receiving-slit width, detector defocus, receiving-slit length and inclusion of a monochromator).
A blueprint for the design of oxide materials is provided by nature. By borrowing from nature's ability to influence inorganic microstructures in biomineralization processes and in the hydrothermal synthesis of complex minerals, a new class of materials in which organic components exert a role in controlling inorganic microstructure is evolving. By employing members of the ever-expanding class of polymeric coordination complex cations, novel molybdenum oxide substructures, such as the one shown, may be prepared.
A strategy based on reticulating metal ions and organic carboxylate links into extended networks has been advanced to a point
that allowed the design of porous structures in which pore size and functionality could be varied systematically. Metal-organic
framework (MOF-5), a prototype of a new class of porous materials and one that is constructed from octahedral Zn-O-C clusters
and benzene links, was used to demonstrate that its three-dimensional porous system can be functionalized with the organic
groups –Br, –NH2, –OC3H7, –OC5H11, –C2H4, and –C4H4 and that its pore size can be expanded with the long molecular struts biphenyl, tetrahydropyrene, pyrene, and terphenyl.
We synthesized an isoreticular series (one that has the same framework topology) of 16 highly crystalline materials whose
open space represented up to 91.1% of the crystal volume, as well as homogeneous periodic pores that can be incrementally
varied from 3.8 to 28.8 angstroms. One member of this series exhibited a high capacity for methane storage (240 cubic centimeters
at standard temperature and pressure per gram at 36 atmospheres and ambient temperature), and others the lowest densities
(0.41 to 0.21 gram per cubic centimeter) for a crystalline material at room temperature.
A combination of framework-builder (Cu(II) ion and 4,4'-bipyridine (4,4'-bpy) ligand) and framework-regulator (AF(6) type anions; A = Si, Ge, and P) provides a series of novel porous coordination polymers. The highly porous coordination polymers ([Cu(AF(6))(4,4'-bpy)(2)].8H(2)O)(n)(A = Si (1a.8H(2)O), Ge (2a.8H(2)O)) afford robust 3-dimensional (3-D), microporous networks (3-D Regular Grid) by using AF(6)(2-) anions. The channel size of these complexes is ca. 8 x 8 A(2) along the c-axis and 6 x 2 A(2) along the a- or b-axes. When compounds 1a.8H(2)O or 2a.8H(2)O were immersed in water, a conversion of 3-D networks (1a.8H(2)O or 2a.8H(2)O) to interpenetrated networks ([Cu(4,4'-bpy)(2)(H(2)O)(2)].AF(6))(n)(A = Si (1b) and Ge (2b)) (2-D Interpenetration) took place. This 2-D interpenetrated network 1b shows unique dynamic anion-exchange properties, which accompany drastic structural conversions. When a PF(6)(-) monoanion instead of AF(6)(2)(-) dianions was used as the framework-regulator with another co-counteranion (coexistent anions), porous coordination polymers with various types of frameworks, ([Cu(2)(4,4'-bpy)(5)(H(2)O)(4)].anions.2H(2)O.4EtOH)(n)(anions = 4PF(6)(-) (3.2H(2)O.4EtOH), 2PF(6)(-) + 2ClO(4)(-) (4.2H(2)O.4EtOH)) (2-D Double-Layer), ([Cu(2)(PF(6))(NO(3))(4,4'-bpy)(4)].2PF(6).2H(2)O)(n)(5.2PF(6).2H(2)O) (3-D Undulated Grid), ([Cu(PF(6))(4,4'-bpy)(2)(MeCN)].PF(6).2MeCN)(n)(6.2MeCN) (2-D Grid), and ([Cu(4,4'-bpy)(2)(H(2)O)(2)].PF(6).BF(4))(n) (7) (2-D Grid), were obtained, where the three modes of PF(6)(-) anions are observed. 5.2PF(6).2H(2)O has rare PF(6)(-) bridges. The PF(6)(-) and NO(3)(-) monoanions alternately link to the Cu(II) centers in the undulated 2-D sheets of [Cu(4,4'-bpy)(2)](n)() to form a 3-D porous network. The free PF(6)(-) anions are included in the channels. 6.2MeCN affords both free and terminal-bridged PF(6)(-) anions. 3.2H(2)O.4EtOH, 4.2H(2)O.4EtOH, and 7 bear free PF(6)(-) anions. All of the anions in 3.2H(2)O.4EtOH and 4.2H(2)O.4EtOH are freely located in the channels constructed from a host network. Interestingly, these Cu(II) frameworks are rationally controlled by counteranions and selectively converted to other frameworks.
Double interpenetration: Guest molecules can control the formation of an unprecedented interlinked network consisting of zinc and a 3D tridentate ligand. The network shrinks when guest molecules are removed and swells when they are returned (see scheme).
Three new cyano-bridged copper(II)−copper(I) mixed-valence polymers containing diamine ligands of formula [Cu(pn)2][Cu2(CN)4] (1, pn = 1,2-propanediamine), [Cu2(CN)3(dmen)] (2, dmen = N,N-dimethylethylenediamine), and [Cu3(CN)4(tmen)] (3, tmen = N,N,N‘,N‘-tetramethylethylenediamine) and one 2D cyano-bridged copper(I) polymer, [NEt4][Cu2(CN)3] (4), have been synthesized. The structural results and DFT calculations show that the architecture of the assembled compound is mainly controlled by the volume of the diamine ligand. Compound 4 shows intense luminiscence at room temperature whereas weak antiferromagnetic interactions are observed for 2 and 3.
The reaction between [Co(H2O)6]2+ and [Co(CN)5]3- in deoxygenated water yields a dark blue solid of composition Co3[Co(CN)5]2.8H2O (1). X-ray powder diffraction data indicate a cubic Prussian blue-type framework, wherein the hexacyanometalate positions have only a two-thirds occupancy of square-pyramidal [Co(CN)5]3- units. Upon dehydration, the compound retains crystallinity and exhibits a Type I dinitrogen sorption isotherm, characteristic of a microporous solid. Magnetic measurements show 1 to behave as a ferrimagnet with an ordering temperature of 48 K, which is reduced to 38 K in the dehydrated solid. At 5 K, both 1 and dehydrated 1 exhibit magnetic hysteresis with a coercive field of 1160 G (the highest value yet reported for a cubic Prussian blue analogue) and remnant magnetizations of 1540 and 745 cm3G/mol, respectively. Thus, dehydrated 1 represents the first compound for which microporosity and long-range magnetic ordering have been demonstrated to coexist.
A hysteretic adsorption and desorption profile (right) accompanied by a transformation of the crystal structure is observed for the title coordination polymer, which possesses a pillared-layer structure (left), on exposure to H2O or MeOH vapor under pressure.
The new complexes trans-[a2Pt(Hpymo-N1)2]X2 (a = NH3, X= NO3 (1a); a = CH3NH2, X= NO3 (1b); a = CH3NH2, X= ClO4 (1c); Hpymo = 2-hydroxypyrimidine) have been prepared by reaction of trans-[a2Pt(H2O)2]-X2 with 2-hydroxypyrimidine at 80 °C in water. Complex 1c cocrystallizes in water with 2-aminopyrimidine (ampym) through formation of complementary pairs of hydrogen bonds to give the supramolecular hexagon {trans-[(CH3NH2)2Pt(pymo-N1)(Hpymo-N1)]·Hampym}2(ClO4)4 (2). Molecular recognition of ampym by 1c is responsible for a conformational change of the two hydroxypyrimidine ligands in 1c from anti (1c) to syn and in addition for a proton transfer from a Hpymo residue to ampym against 1.5 units of pK(a) gradient. 1H NMR concentration-dependent studies as well as NOE experiments in dmso-d6 and dmf-d7 show that 2 dissociates in solution. Compound 1a reacts in NH3:H2O (1:3) with Ag(I) to give the polymeric species {trans-[(NH3)2Pt(μ-pymo-N1,N3)2Ag(H2O)]-NO3}(n) (3). In contrast to 2, in the polymeric structure the trans-[(NH3)2Pt(pymo)2] entities adopt an anti conformation. Nevertheless, the [(H2O)Ag(pymo)2] residues present a syn conformation that leads to a meander-like global structure. Compounds 1b, 1c, 2, and 3 have been studied by X-ray crystallography: (1b) triclinic space group, P1̄, a = 9.300(2) Å, b = 10.483(2) Å, c = 11.050(2) Å, α = 68.21(3)°, β = 75.47(3)°, γ = 73.83(3)°, Z = 2, R1 = 0.025, and wR2 = 0.062; (1c) triclinic space group, P1̄, a = 5.692(1) Å, b = 7.758(2) Å, c = 11.236(2) Å, α = 93.12(3)°, β = 92.86(3)°, γ = 102.58(3)°, Z = 2, R1 = 0.048, and wR2 = 0.119; (2) triclinic space group, P1̄, a = 8.355(2) Å, b = 11.221(2) Å, c = 13.004(3) Å, α = 86.76(3)°, β = 78.62(3)°, γ = 77.96(3)°, Z = 2, R1 = 0.033, and wR2 = 0.080; (3) monoclinic space group, C2/c, a = 5.345(1) Å, b = 23.998(5) Å, c = 12.474(2) Å, β = 102.27(3)°, Z = 8, R1 = 0.041, and wR2 = 0.093.
Flexible and dynamic coordination polymers based on interpenetration and interdigitation have been synthesized and characterized. Reversible crystal-to-crystal transformation from a nonporous structure (24 m2g-1) to a microporous structure (at least 320 m2g-1) is triggered by adsorption of various supercritical gases (see picture).
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