3D coordination polymers with vanadyl fragments and alkaline earth metal ions

The reactions of vanadyl sulfate VOSO₄·3H₂O with barium or strontium cyclopropane-1,1-dicarboxylate (MCpdc, M = Ba, Sr, H₂Cpdc = C₃H₄(COOH)₂) afforded the polymeric heterometallic complexes {[(H₂O)₈Ba₂(VO)₂(Cpdc)₄]·2H₂O}n (1) and {[(H₂O)₆Sr(VO)(Cpdc)₂]}n (2), respectively. These complexes differ in the binding mode of mononuclear vanadyl fragments with alkaline earth metal ions. Coordination polymers 1 and 2 were characterized by ESR spectroscopy.     

Synthesis of a diazacrown ether containing polymers and formation of complexes with alkaline earth metals

We report the synthesis of a polymer that contains the diaza‐18‐crown‐6 moiety on the polymer main chain. Metal containing polymers were obtained when the respective barium or strontium complexes were used as monomers. These polymers emitted greenish blue light in solution, and the metal had little influence on absorption and emission energies. In the solid state, the position of the emission peaks was different probably due to a different degree of aggregation.     

Tuning aromaticity in trigonal alkaline earth metal clusters and their alkali metal salts

In this work, we analyze the geometry and electronic structure of the [X_nM₃]^n?2 species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo‐[M₃]^2? unit. The cyclo‐[M₃]^2? ring is held together through a three‐center two‐electron bond of σ‐character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo‐[M₃]^2? ring and leads to a change from σ‐aromaticity in the bound state of the cyclo‐[M₃]^2? to π‐aromaticity in the XM₃^? and X₂M₃ metallic clusters. Our results also show that the aromaticity of the cyclo‐[M₃]^2? unit in the X₂M₃ metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M₃ ring. The Na₂Mg₃, Li₂Mg₃, and X₂Ca₃ clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M₃ ring, whereas X₂Be₃ and K₂Mg₃ keep its aromaticity relatively constant along this process. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

3d and 4d coordination complexes and coordination polymers involving electroactive tetrathiafulvalene containing ligands

The “through bond” approach has been recently developed to increase the interaction between the mobile π and localized d electrons in multifunctional molecular materials involving tetrathiafulvalene-based ligands. This article reviews the 3d and 4d coordination complexes and polymers elaborated from a library of tetrathiafulvalene derivatives containing ligands obtained recently in our group. The different synthetic ways of the complexes are highlighted as well as their chemical and physical properties.     

Macromolecules containing bipyridine and terpyridine metal complexes: towards metallosupramolecular polymers

The ability of a broad range of N-heterocycles to act as very effective and stable complexation agents for several transition metal ions, such as cobalt(II), copper(II), nickel(II), and ruthenium(II), has long been known in analytical chemistry. This behavior was later utilized in supramolecular chemistry for the construction of highly sophisticated architectures, such as helicates, racks, and grids. The discovery of macromolecules by Staudinger in 1922 opened up avenues towards sophisticated materials with properties hitherto completely unknown. In the last few decades, the combination of macromolecular and supramolecular chemistry has been attempted by developing metal-complexing and metal-containing polymers for a wide variety of applications that range from filtration to catalysis. The stability of the polymer-metal complex is a fundamental requirement for such applications. In this respect, the use of bi- and terpyridines as chelating ligands is highly promising, since these molecules are known to form highly stable complexes with interesting physical properties with transition-metal ions. A large number of different structures have been designed for many different applications, but polymers based on the application of coordinative forces have been prepared in a few cases only. Furthermore, the synthetic procedures applied frequently resulted in low yields. During the last few years, strong efforts have been made in the direction of self-assembling and supramolecular polymers as novel materials with "intelligent" and tunable properties. In this review, an overview of this active area at the interface of supramolecular and macromolecular chemistry is given.     

Syntheses,crystal structures and thermoanalyses of alkaline earth metal complexes derived from dinitropyridone

Six new alkaline-earth metal compounds derived from dinitropyridone ligands (3,5-dinitropyrid-2-one, 2HDNP; 3,5-dinitropyrid-4-one, 4HDNP and 3,5-dinitropyrid-4-one-N-hydroxide, 4HDNPO) were synthesized and characterized by elemental analysis, FT-IR and partly by powder XRD, TG-DSC and X-ray single-crystal diffraction analysis. The structural determination revealed that one molecule of both magnesium salts (Mg(2DNP)₂ ·?8H₂O, (1), and Mg(4DNP)₂ ·?6H₂O (4)) comprise one cation [Mg(H₂O)₆]²⁺ and two anions displaying centro-symmetry with the Mg atom located at the center. Two anions (and crystalline water molecules) are joined by hydrogen bonds. The barium salt Ba(4DNP)₂ ·?4H₂O (5), is a centro-symmetric dimer with each Ba(II) being coordinated by one monodentate ligand anion, two bidentate ligand anions (different coordination pattern) and five water molecules. Another barium salt, Ba(4DNPO)₂ ·?6H₂O (6), is a coordination polymer, the ten-coordinate (BaO₁₀) barium environment comprising four water molecules, a pair of 4DNPOs via the pyridine-N-oxide oxygen, and one 4DNPOs from an adjacent metal atom offering chelating nitro group oxygen, bridging adjacent bariums. Abundant intermolecular hydrogen bonds link the molecules of each complex into multi-dimensional chains. The X-ray powder diffraction analysis confirmed the phase homogeneity of the polycrystalline samples. The TG-DSC results revealed that Mg(2DNP)₂ ·?8H₂O and Ba(4DNP)₂ ·?6H₂O each has three main weight-loss stages. The first step is the loss of all water molecules and the last step is the loss of the nitro groups and/or decomposition of the pyridine rings with the release of heat.     

Supramolecular structures and stereochemical versatility of azoquinoline containing novel rare earth metal complexes

Rare earth complexes of 5-(phenylazo)-8-hydroxyquinoline (HL) of composition [M(L)(2)X.H(2)O] [where M=La, Ce, Pr, Nd and X=NO(3)(-) or NCS(-)] have been prepared and characterized on the basis of their chemical analyses, (1)H NMR, magnetic measurements, conductance, and visible and IR spectral data. Composition, conductance and IR spectral data of the complexes show that the HL acts as a bidentate monobasic ligand. The visible spectra of Pr(3+) and Nd(3+) show characteristic f-f transitions, and the nephelauxetic effect (1-beta) of these transitions has been evaluated. These data indicate the weak involvement of the 4f orbitals in complex formation.     

Compressed octahedral coordination in chain compounds containing divalent copper: structure and magnetic properties of CuFAsF6 and CsCuAlF6

Crystal structures and magnetic investigations of CuFAsF6 and CsCuAlF6 are reported. Together with KCuAlF6, these appear to be the only examples of Jahn-Teller pure Cu(II) compounds containing only one type of ligand that exhibits a compressed octahedral coordination geometry. The Rietveld method has been used for refining the CsCuAlF6 structure based on neutron powder diffraction data at 4 K. The compound crystallizes in space group Pnma (no. 62) with a=7.055(1), b=7.112(1), c=10.153(1) A and Z=4 at 4 K. The structure is built from infinite [CuF5]n(3n-) chains of [CuF6]4- octahedra running along the [1 0 0] direction and (AlF6)3- octahedra connected by corners in the trans position, thus giving rise to chains oriented along the [0 1 0] direction. Single crystals of CuFAsF6 were prepared under solvothermal conditions in AsF5 above its critical temperature. The structure was determined from single-crystal data. CuFAsF6 crystallises in the orthorhombic space group Imma (No. 74) with a=10.732(5), b=6.941(3), c=6.814(3) A and Z=4 at 200 K. The structure can also be described in terms of one-dimensional infinite [CuF5]n(3n-) chains of tilted [CuF6](4-) octahedra linked by trans-vertices running along the b axis. The [CuF5]n(3n-) chains are connected through [AsF6]- units sharing joint vertices. The compressed octahedral coordination of CuII atoms in CuFAsF6 and CsCuAlF6 compounds at room temperature is confirmed by Cu K-edge EXAFS (extended x-ray absorption fine structure) analysis. For both compounds strong antiferromagnetic interactions within the [CuF5]n(3n-) chains were observed (theta(p)=-290+/-10 K and theta(p)=-390+/-10 K for CuFAsF6 and CsCuAlF6, respectively). The peculiar magnetic behaviour of chain compounds containing divalent copper at low temperature could be related to uncompensated magnetic moments in the one-dimensional network.     

Weak alkali and alkaline earth metal complexes of low molecular weight ligands in aqueous solution

This work is aimed at reviewing the chemical literature dealing with thermodynamic aspects of the weak complex formation (species with log K values less than about 3) between alkali and alkaline earth metal ions with low molecular weight inorganic and organic ligands in aqueous solution. The following ligands (up to hexavalent anions) were examined in detail: (i) hydroxide, chloride, sulfate, carbonate and phosphate as inorganic, and (ii) carboxylates, amines, amino acids, complexones and nucleotides as organic ligands. The paper also identifies the main reasons responsible for the dispersion of the stability data on ion pairs in the literature. When possible, the trend of stability for the different metal ions interacting with the same ligand will be considered to find predictive interaction relationships. Since the stability of weak alkali and alkaline earth metal complexes are mainly due to electrostatic interaction, simple empirical relationships were obtained between log K and the charge of the anionic ligand. The interest for alkali and alkaline earth cations rises since they are used in study of basic science as components of the supporting electrolyte and are widely diffused in natural fluids. Some examples of application of this science were presented too, to show the role of weak complex formation in the modelling process of natural systems.     

碱土金属与DBC-偶氮氯膦配位反应及配合物结构的研究

本文研究了DBC-偶氮氯膦在不同酸度下的存在形式、质子化情况及反应中的质子释放情况, 测定了钙、锶、钡与其形成的配合物的稳定常数。利用红外、激光Raman、核磁共振光谱等对所生成的配合物的结构进行了研究, 并根据实验结果和分子结构的几咱理论, 提出了碱土金属与其生成的配合物的结构。本文还就配位反应和配合物的成键情况进行了讨论。     

A novel layered niobium oxychloride compound based on Nb2 pairs and Nb6 octahedral clusters: synthesis and crystal and electronic structures of Nb10Cl16O7

The synthesis, single crystal structure determination, and electronic structure of Nb10Cl16O7, the first Nb6 oxychloride stabilized without countercation, are reported in this work. The crystal structure is very original since it consists of layers built up from both Nb6 octahedral clusters and Nb2 pairs. The Nb6Oi6Cli6Cla6 and Nb2(mu2-Cl)2Cl4O4 units form [Nb6Cli6Oi4O(i-i)(2/2)Cl(a-a)(4/2)Cla2]infinity infinite chains and [(Nb2(mu2-Cl)2O(2/2)Cl(4/2)O2)2]infinity double chains, respectively, that are interconnected by shared oxygen and chlorine ligands leading to layers. The cohesion of the three-dimensional structure (3D) is ensured by van der Waals contacts between layers that are randomly stacked along the [011] direction. Structural correlations between Nb10Cl16O7 and related Nb6 cluster oxyhalides, as well as NbOCl2 and NbCl4 containing Nb2 pairs, are discussed. DFT results show that among the 20 valence electrons involved in the metal-metal bonding states, 14 electrons belong to the octahedral Nb6Cli6Oi6Cla6 unit whereas the 6 others (i.e., 1.5 per Nb atom) participate in the bonding in the distorted [(Nb2(mu2-Cl)2O(2/2)Cl(4/2)O2)2]infinity double chains.     

New coordination cyano-bridged polymers based on tetranuclear rhenium chalcocyanide clusters and copper(ii) ammonia complexes

The reactions of aqueous solutions of the tetranuclear chalcocyanide cluster anions [Re₄Q₄(CN)₁₂]^4–, where Q = S, Se, or Te, with an ammonia solution of copper(ii) chloride at room temperature afforded a series of polymeric cyano-bridged compounds [{Cu(NH₃)₃}₂{Re₄Q₄(CN)₁₂}]·nH₂O (Q = S (1), Se (2)) and [{Cu(NH₃)₃}_1.7{Cu(NH₃)₄}_0.3Re₄Te₄(CN)₁₂] (3) having chain structures. The structures of the compounds were established by X-ray diffraction analysis. Compounds 1 and 2 are isostructural and have ordered structures. In structurally similar compound 3, the copper atoms are disordered over two positions in such a way that the structure contains the bridging {Cu(NH₃)₃} fragments along with the terminal {Cu(NH₃)₄} fragments.     

Solvent‐free alkali and alkaline earth metal complexes of di‐imine ligands

Compound [(dph‐BIAN)Mg(THF)]₂ ( 2 ) was prepared by reacting magnesium metal with 1,2‐bis[(2‐biphenyl)imino]acenaphthene (dph‐BIAN) in THF, followed by crystallization from toluene. Reaction of CaI₂ with (dpp‐BIAN)Li₂ in toluene afforded [(dpp‐BIAN)Li]₂Ca ( 3 ) (dpp‐BIAN = 1,2‐bis[(2,6‐diisopropylphenyl)imino]acenaphthene). Both complexes 2 and 3 were characterized by single crystal X‐ray diffraction. The ¹H NMR spectroscopic data obtained for complex 3 in toluene solution indicated an agostic interaction between the methyl groups of the ligand and lithium atoms. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:663–670, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20168     

Study of doubly charged alkaline earth metal and 3-azidopropionitrile complexes by electrospray ionization mass spectrometry

The present work describes a study of the complexation of calcium and magnesium by 3-azidopropionitrile by means of electrospray ionization mass spectrometry (ESI-MS). Complexes were obtained from solutions of calcium and magnesium salts of the type CaX2 and MgX2 (where X = Cl or NO3) in water and methanol/water. The complexes detected were mainly double positively charged, with various stoichiometries not depending on the solvent, since water and 3-azidopropionitrile were always the main ligands. Solvation with methanol was not observed unlike in a previous study of complexation of nickel and cobalt by 3-azidopropionitrile. The complex ions [M(II)Az4(H2O)](2+), [M(II)Az5](2+) (where M = Ca and Mg) are the most abundant for both metals, and both counter ions. Tandem mass spectrometric (MS/MS) analysis showed that, under collision-induced dissociation (CID) conditions, the most important processes occurring were loss of neutral ligands and the replacement of 3-azidopropionitrile by water. A complex species containing reduced alkaline earth metal was due to radical loss, resulting from homolytic cleavage in the azide ligand. Some terminal ions, in the fragmentation sequences, point to the nitrile group as the coordination site in the 3-azidopropionitrile. Density functional theory (DFT) calculations confirmed this coordination site and proved that 3-azidopropionitrile behaves as a monodentate ligand in the systems under study. Moreover, the theoretical study proved that the presence of water ligand introduces stability through a hydrogen bond established between the water molecule and one nitrogen atom of the azido group. In addition, the strong dipole moment of 3-azidopropionitrile (4.76 D), which is mainly related to presence of the nitrile group, favors the stabilization of the metal-ligand complexes through charge-dipole interactions and the coordination of the metal to the nitrile group.     

The photochemistry of a bis-crown ether based on benzobis(thiazole) and its alkaline earth metal cation complexes

Irradiation of acetonitrile solutions of the bis-crown ether E,E-2,7-bis[2-(6,7,9,10,12,13,15,16-octahydro-5,8,11,14,17-pentaoxabenzocyclopentadecen-2-yl)vinyl]-benzo[1,2-d;3,4-d']bisthiazole (hereafter, 1) gives efficient E --> Z photoisomerization (initial phi(trans --> cis) = 0.48), leading to lambda(exc)-dependent quasi-photostationary states composed primarily of E,Z and E,E isomer mixtures. Further irradiation gives [2 + 2]-cycloadducts of 1. In the presence of Ba2+ ions, essentially quantitative formation of 2:2 complexes, 1(2) x (Ba2+)2 controls the photochemical outcome. E --> Z photoisomerization of the ligand is entirely suppressed and efficient intramolecular [2 + 2]-photocycloaddition in the complexes leads to cyclobutane dimers of 1 (phiCB = 0.26). The reactivity of 1 in the presence of Mg2+ ions for which 1:2 complex formation dominates gives both cis-trans photoisomerization and enhanced photocycloaddition.     

Hydrogenation of carbon monoxide by tetranuclear rare earth metal polyhydrido complexes. Selective formation of ethylene and isolation of well-defined polyoxo rare earth metal clusters

The reaction of the tetranuclear rare earth metal polyhydrido complexes {Cp'Ln(mu-H)2}4(THF) (Cp' = C5Me4SiMe3, Ln = Y (1a), Lu (1b)) with carbon monoxide (1 atm) yielded ethylene and the corresponding tetraoxo cubane complexes (Cp'Ln)4(mu3-O)4 (Ln = Y (5a), Lu (5b)). Stepwise formation of some key reaction intermediates, such as oxymethylene complexes (Cp'Ln)4(mu-OCH2)(mu-H)6(THF) (Ln = Y (2a), Lu (2b)), enolate species (Cp'Y)4(OCH=CH2)(mu-O)(mu-H)5(THF) (3), and dioxo complex (Cp'Y)4(mu3-O)2(mu-H)4(THF) (4), was confirmed. The molecular structures of 2a, 4, and 5b were determined by X-ray diffraction studies.     

Assembly of CdI2-type coordination networks from triangular ligand and octahedral metal center: topological analysis and potential framework porosity

Reaction of a rigid triangular ligand 2,4,6-tris[4-(1H-imidazole-1-yl)phenyl]-1,3,5-triazine (TIPT) with Cd2+ ions affordedrare non-interpenetrating CdI2-type networks which display high thermostability and potential porosity; the topological character of the CdI2-type networks have been analyzed in comparison with three common uniform (4,4), (6,3) and (3,6) plane nets.