Ligand-induced polyhedral opening in the mixed-metal cluster MeCCo2NiCp(CO)6 by 4,5-Bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd): X-ray structure of Co2NiCp(CO)4[μ2,η2,η1-C(Me)C=C(PPh2)C(O)CH2C(O)](μ2-PPh2)

The mixed-metal cluster MeCCo₂NiCp(CO)₆ (1) reacts with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in refluxing CH₂Cl₂ to afford the disubstituted cluster MeCCo₂NiCp(CO)₄(bpcd) (2), which exists as a 1:1 mixture of bridging and chelating bpcd isomers. VT ³¹P NMR spectroscopy confirms that the two bpcd isomers do not interconvert in solution over the temperature range of 182–298 K. Thermolysis of cluster 2 leads to bpcd/cluster activation and formation of the phosphido-bridged cluster Co₂NiCp(CO)₄[μ₂,η²,η¹-C(Me)C=C(PPh₂)C(O)CH₂C(O)](μ₂-PPh₂) (3). The ligand-induced polyhedral expansion that accompanies the formation of the title cluster was established by X-ray diffraction analysis. Co₂NiCp(CO)₄[μ₂,η²,η¹-C(Me)C=C(PPh₂)C(O)CH₂C(O)](μ₂-PPh₂) crystallizes in the triclinic space group P-1, a=9.679(2), b=11.691(2), c=16.653(3) ?, α=85.849(3)°, β=85.456(4)°, γ=66.453(3)°, V=1720.3(6) A³, Z=2, D _cacl=1.632 Mg/m³; R=0.0874, R _w=0.1998 for 7053 observed reflections with I > 2σ(I).     

Reactivity of polyiodide toward 1, 3-bis(4-pyridyl)propane (bpp): synthesis and structure of an organic-inorganic hybrid compound [(CuI2)2(N,N′-dimethyl-bpp)] n

The solution-phase reaction of a metal iodide with 1, 3-bis(4-pyridyl)propane (bpp) yields a new organic-inorganic hybrid framework, [(CuI2)2(N,N-dimethyl-bpp)] _n (1), which is made up of organic cations [dimethyl-bpp]²⁺ and an infinite [Cu₂I₄] _n ²⁻ anion chain; The cluster 1 obtained via the reaction between polyiodide complexes and organic N-donor ligand suggests that this simple synthetic approach is likely to be applicable to the construction of polymeric clusters.Supplementary material CCDC-253123 contains the crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44-1223-336-033; E-mail: deposit@ccdc.cam.ac.uk].     

Molecular and crystal structures of decamethylruthenocene (η5-C5Me5)2Ru in the temperature range 153–300 K: Thermal motion in a crystal according to X-ray diffraction data

The crystal structure of decamethylruthenocene (η⁵-C₅ Me ₅)₂Ru (I) is investigated by X-ray diffraction. It is demonstrated that the compound studied crystallizes in two polymorphic modifications, namely, modification Ia with space group P2₁/m (Z = 2) in the temperature range 153–300 K and modification Ibwith space group P2₁/n (Z = 4) at 203 K. No temperature phase transition between the modifications is found. In crystal Ia, the molecule occupies a special position in the mirror plane. In crystal Ib, the molecule is located in the general position. The cyclic ligands η⁵-C₅ Me ₅, (Cp*) are aligned parallel to each other and adopt an eclipsed conformation. The bond lengths in compounds Ia and Ib are identical. Analysis of the anisotropic displacement parameters of the atoms indicates that molecules Ia and Ib are not structurally rigid and that the Cp* rings involved in these molecules can execute independent librations. In the temperature range 153–300 K, the Cp*(1) ligand in molecule Ia is statically disordered over two positions. The barrier heights B ₅ for rotation of the Cp* ligands are estimated both from the root-mean-square amplitudes of librations 〈ϕ²〉 and with the use of the atom-atom potential method. __________ Translated from Kristallografiya, Vol. 48, No. 2, 2003, pp. 283–292. Original Russian Text Copyright ? 2003 by Zanin, Antipin.     

Strontium-based Mercury Cuprates with Perovskite-like Crystal Structures

Conditions of synthesis, structure, and temperatures of superconducting transitions of strontium-based mercury cuprates Hg—Sr—Me—Cu—O (Me = Ca, La, Ce, Sm, Ho) with perovskite-like crystal structure are described. The samples belong to two homological series: HgSr₂ (Ln, Ce)_n–1CunO_2n + _{2 + δ} with the Hg—O bond directed along <110> and (Hg, Cu) Sr₂Ln_n–1Cu_nO_{2n + 2 + δ} with the (Hg, Cu)—O bond directed along <100>. The variation of composition leads to rotation of the Hg—O bond along the hk0 direction and consequently to the increase of T_c from 28 K to 81 K. An anomaly of the resistivity was observed around 200 K for most of the investigated samples, independent of their content and phase composition.     

1-[Ferrocenyl(hydroxy)methyl]-1,7-dicarba<Emphasis Type="Italic">-closo</Emphasis>-dodecaborane: Synthesis and X-ray crystal structure

The synthesis and molecular structure of the novel 1-[ferrocenyl(hydroxy)methyl]-1,7-dicarba-closo-dodecaborane (1) is described. Compound 1 was synthesized from reaction of m-carborane and ferrocene carboxaldehyde using n-butyllithium (n-BuLi) or tetrabutylammonium fluoride (TBAF) in THF in 45% and 36% yield, respectively. Compound 1 consists of a ferrocene molecule tethered to m-carborane through a methylhydroxy bridge. The crystal structure of 1 was determined by single crystal X-ray diffraction analysis. Crystal data: 1 [Fe(C₅H₅)(C₅H₄-CH₂O-1,7-C₂B₁₀H₁₂)], formula weight = 359.17, crystallized in orthorhombic system, space group Pna2 ₁ with a=19.698(4) ?, b=10.709(2) ?, c=8.520(2) ?, and V=1797.3(7) ?³ and Z=4. Refined to R ₁=0.043 for 4124 observed reflections with I/σ>2σ(I). The compound was crystallized as racemic twins in a ratio of 73(2)/27(2). The unsubstituted Cp ring was disordered and modeled as two conformations in a 53(3)/47(3) ratio. Intermolecular hydrogen bonding was observed from the hydrogen of the meta-carbon on the carborane cluster towards the hydroxyl oxygen.     

Preparation and Reactivity of 4,4′-diaminostilbene-2,2′disulphonate

The precursor compound 4,4′-diaminostilbene-2,2′disulphonic acid DAS-(SO₃H)₂ was successfully deprotonated through reactions with (n-Bu₄N)(OH) and NaOH to produce the corresponding salts sodium 4,4′-diaminostilbene-2,2′disulphonate Na₂(DAS-(SO₃)₂) (1) and tetrabutylammonium 4,4′-diaminostilbene-2,2′disulphonate (n-Bu₄N)₂(DAS-(SO₃)₂) (2). The structure of (n-Bu₄N)₂(DAS-(SO₃)₂) (2) was confirmed through the use of single crystal X-ray diffraction. Compound (2) crystallizes in the monoclinic space group P2₁/n with the lattice parameters of a = 10.0645(6), b = 14.2573(9), c = 17.6053(11), and β = 94.3160(10). The reaction of Cu²⁺(aq) with (n-Bu₄N)₂(DAS-(SO₃)₂) resulted in the crystallization of the molecular organocopper cluster, [CuDAS-(SO₃)₂]₂·3H₂O (3), that resembles a molecular parallelogram as revealed by single crystal X-ray diffraction. Compound (3) crystallizes in the monoclinic space group P2₁/n with the lattice parameters of a = 8.8647(6), b = 10.5247(7), c = 21.2265(14), and β = 93.1730(10). Within the structure of (3) each [DAS-(SO₃)₂]²⁻ ligand is shown to bind two copper atoms through interactions with three of the five available metal binding sites.

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Graphical abstract Preparation and Reactivity of 4,4′-diaminostilbene-2,2′disulphonate Natalie C. Rader, Heather A. Nees, Paul S. Szalay*, Matthias Zeller and Allen D. Hunter The preparation of 4,4′-diaminostilbene-2,2′disulphonic and its reactivity with copper(II) are described.

     

Synthesis and Crystal Structures of Anionic Gallium(II) and Gallium(III) Heterocyclic Compounds Derived from a Gallium(I) N-Heterocyclic Carbene Analogue

Abstract  

The addition of the N–H bond of the formamidine, ArN(H)C=NAr (Ar = C₆H₃Pr₂ⁱ-2,6), to the gallium(I) center of [K(tmeda)][:Ga(Ar-DAB)] (Ar-DAB={(Ar)NC(H)}₂) yields K[(Ar-DAB)Ga^III(H){N(Ar)C=NAr}] 1. The crystal structure of this and two other related anionic compounds, [K(18-crown-6)][(Ar-DAB)Ga^III{N(H)N=Fl}{(H)Fl}] (Fl = fluorendiyl) 2 and [K(OEt₂)₃][(Ar-DAB)Ga^II(CH₂Ph)Ga^II(Ar-DAB)] 3, have been determined. The cell parameters of the compounds are 1: P2₁/c, a = 20.2350(9), b = 14.1760(7), c = 19.6441(10), β = 111.307(1); 2: P2₁/c, a = 13.115(3), b = 21.799(4), c = 22.646(5), β = 90.20(3); 3: P2₁/n, a = 16.783(3), b = 21.635(4), c = 19.814(4), β = 92.34(3). The crystal structures of all complexes exhibit distorted tetrahedral gallium centers, and interactions between anion aryl substituents and the potassium cations.     

Mesophase design: I. Molecular structure and crystal packing motifs of 4-alkylcyanobiphenyls

A comparative study of the crystal and molecular structures of 4-alkylcyanobiphenyls (ACB-n) C _n H_{2n + 1}-C₆H₄-C₆H₄-CN (n = 2, 4–12) belonging to liquid-crystal compounds revealed no direct relationship between the molecular geometry of these compounds and their liquid-crystalline properties. Mesogenic properties are determined by the alternation of the loosely packed aliphatic and closely packed aromatic regions in the crystals. Graphs describing the crystals and mesophases were designed for ACB-n. The graph for nematic mesogens of ACB-n (n = 5−7) has one structure-forming element. The graph for smectic-nematic (n = 8 and 9) and smectic (n = 10−12) mesogens have more than one structure-forming element. If different types of secondary bonds in the smectic mesophase have equal energies, the disruption of these interactions caused by the temperature rise occurs simultaneously and the system undergoes a transition from the smectic phase to the isotropic liquid. If the energies of different types of secondary bonds are different, the destruction of the mesophase occurs in steps and the phase transitions are more complicated (smectic-nematic-isotropic transitions).     

Syntheses and X-ray structures of the bridging and chelating isomers of Os3(CO)10(dmpe)

The substitution chemistry of the activated clusters Os₃(CO)₁₀(MeCN)₂ (1) and Os₃(CO)₁₀(1,5-cod) (2) has been investigated with the bidentate ligand 1,2-bis(dimethylphosphino)ethane (dmpe). Both starting clusters react rapidly with dmpe at room temperature to give the corresponding substitution product Os₃(CO)₁₀(dmpe) (3), whose isomeric composition is shown to depend on the nature of the starting cluster. Whereas the bridged cluster 1,2-Os₃(CO)₁₀(dmpe) (3b) was formed almost exclusively upon reaction with Os₃(CO)₁₀(MeCN)₂, a near statistical mixture of bridging (3b) and chelating (3c) isomers of Os₃(CO)₁₀(dmpe) was found in the reaction employing Os₃(CO)₁₀(1,5-cod). Both dmpe isomers have been characterized in solution by 3iP NMR spectroscopy and their solid-state structures established by X-ray crystallography. The bridged cluster 1,2-Os₃(CO)₁₀(dmpe) crystallizes in the monoclinic space group P2₁/n, a = 9.867(2) Å, b = 17.081(3) Å, c = 14.198(2) Å, β = 95.902(3)°, V = 2380.4(6) ų, Z = 4, and d _calc = 2.793 Mg/m³; R = 0.0435, R _w = 0.0466 for 3519 reflections with I > 2σ(I). The chelated cluster 1,1-Os₃(CO)₁₀(dmpe) crystallizes in the orthorhombic space group C222(1), a = 8.329(3) Å, b = 19.028(6) Å, c = 15.008(5) Å, V = 2379(1) ų, Z = 4, and d _calc = 2.795 Mg/m³; R = 0.0390, R _w = 0.0718 for 2360 reflections with I > 2σ(I).     

Crystallographic and luminescence studies of ammonium and water adducts of anthraquinone fluorophores

Fluorescence and X-ray crystallographic results for ammonium adducts of an anthraquinone-containing polyether macrocycle, 1,8-oxybis(ethyleneoxyethyleneoxy)-anthracene-9,10-dione (1), and an open-chain fluorinated analogue are presented. The crystal structure of a pseudo-polymorph of a hydrate of compound 1 is also presented. [1 ₂·NH₄]PF₆·MeOH (2), triclinic, P-1, a=10.5948(13), b=14.903(2), c=15.918(2), α=71.260(3), β=82.063(2), γ=69.258(2), Z=2, 5250 reflections [I≥2σ(I)], R₁=0.0487, wR₂=0.1190, 173(2) K; 1 ₄ ·H₂O, Triclinic, P-1, a=12.0084(8) b=13.8050(9) c=23.8027(16), α=106.068(1), β=98.281(1), γ=90.047(1), Z=8, 8402 reflections [I≥2σ(I)], R₁=0.0488, wR₂=0.1086, 100(2) K. Different anti and gauche ring conformations are observed for macrocycles with and without guests complexed within the polyether ring.     

Three New Complexes Based on a Flexible Bis(benzimidazole) Ligand and Rigid/Flexible Organic Carboxylates

Abstract  

Three new polymeric frameworks, [Ni(bbbm)(L1)₂] _n (1), [Ni(bbbm)(L2)₂] _n (2), and {[Co(bbbm)(L3)]·H₂O} _n (3) (bbbm = 1,4-bis(N-benzimidazolyl) butane, HL1 = 4-bromobenzoic acid, HL2 = 3-methylbenzoic acid, and H₂L3 = glutaric acid) have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Complex 1 features a one-dimensional (1D) linear chain structure bridged by bbbm ligands, which is further connected into a supramolecular double chain structure through intermolecular π–π stacking interactions. Complex 2 contains 1D zigzag chain, which is further arranged into a 2D supramolecular architecture by hydrogen bonding and π–π stacking interactions. In the structure of 3, there are infinite 1D zigzag Co(II)-bbbm chains linked together by L3 ligands to generate an undulated 2D (4,4) sheet, which is further connected by intermolecular π–π stacking interactions to form a 3D supramolecular network. Furthermore, thermal stability and luminescent property of 1–3 were investigated.     

A density functional theory study on multiple exciton generation in lead chalcogenides

Abstract

Quantum confined structure-based solar cell is promising two folds increment of the maximum theoretical photovoltaic conversion efficiency i.e., > 60% in comparison with that of the bulk analogs e.g., silicon-based and dye sensitized solar cell (ca. 32% of maximum theoretical efficiency). The key to the significant increment is the ability of the fluorophore to exhibit multiple exciton generation upon absorption photon with sufficient energy. Small size of lead chalcogenides (PbS, PbSe, PbTe) crystals have been reported and proven experimentally could exhibit this unique property. We have investigated few clusters of narrow bandgap lead chalcogenides nanocrystals i.e., (PbS)n, (PbSe)n and (PbTe)n; which n?=?4 - 80. The cluster models were optimized using quantum chemical calculations to the lowest energy geometry at B3LYP/lanl2dz level of theory. The predicted realistic (PbS)₈₀, (PbSe)₅₀, and (PbTe)₇₄ clusters with the size, and bandgap of 4.58?nm (2.00?eV), 4.03?nm (1.51?eV), and 4.84?nm (1.55?eV) are smaller than that of their exciton Bohr radius i.e., 5.01, 13.1, and 24.8?nm respectively. Therefore, the occurrence of multi exciton generation in the clusters is hypothesized upon absorption of photon with E_photon = 2E_g.     

Syntheses, Characterizations and Crystal Structures of Two Copper Coordination Polymers Both Having Cu2Cl2 Bridging Subunit [CuI(bipy)1/2Cl]n(1) and {[(CuII)4(phen)4(SSA)2Cl2](H2O)2(DMF)2}n(2)

Abstract  

Two copper coordination polymers [Cu^I(bipy)_1/2Cl] _n (1) and {[(Cu^II)₄(phen)₄(SSA)₂Cl₂] (H₂O)₂(DMF)₂} _n (2)(bipy = 4,4′-bipyridine, phen = 1,10-phenanthroline, H₃SSA = 5-sulfosalicylic acid, DMF = N,N-dimethylformamide) have been prepared and characterized by X-ray diffraction, elemental analysis, IR spectrum and 2 was also studied by cyclic voltammetric method. X-ray analysis indicates that both of them have Cu₂Cl₂ bridging subunit. Complex 1 is a two dimensional network structure. While 2 shows a one dimensional zigzag chain. Electrochemistry studies reveal that complex 2 undergo a quasi reversible one-electron metal-centered redox process at E _1/2 = +0.062 V.     

Diphosphine ligand substitution in H4Ru4(CO)12: X-ray diffraction structures and reactivity studies of the cluster compounds H4Ru4(CO)10(P–P) [where P–P–(Z)–Ph2PCH–CHPPh2, bpcd]

The tetraruthenium cluster H₄Ru₄(CO)₁₂ (1) has been studied for its reactivity with the unsaturated diphosphine ligands (Z)–Ph₂PCH–CHPPh₂ and 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) under thermal, near-UV photolysis, and Me₃NO-assisted activation. All three cluster activation methods promote loss of CO and furnish the anticipated substitution products H₄Ru₄(CO)₁₀[(Z)–Ph₂PCH–CHPPh₂] (2) and H₄Ru₄(CO)₁₀(bpcd) (3) that possess a chelating diphosphine ligand. Clusters 2 and 3 have been characterized in solution by IR and NMR spectroscopies, and these data are discussed with respect to the crystallographically determined structure for both new cluster compounds. The ³¹P NMR spectral data and the solid-state structures confirm the presence of a chelating diphosphine ligand in clusters 2 and 3. Cluster 2 crystallizes in the monoclinic space P2₁/c, a=11.768(6) ?, b=18.521(9) ?, c=20.48(1) ?, β=102.291(8)°, V=4361(4) A³, Z=4, and d _calc=1.726 Mg/m³; R=0.0225, R _w=0.0491 for 6798 reflections with I > 2σ(I). The four bridging hydrides were located in H₄Ru₄(CO)₁₀[(Z)–Ph₂PCH–CHPPh₂] and their adopted positions are discussed relative to the solution ¹H NMR spectrum. H₄Ru₄(CO)₁₀(bpcd) crystallizes in the orthorhombic space Pbca, a=19.072(3) ?, b=20.169(3) ?, c=22.774(3) ?, V=8760(2) A³, Z=8, and d _calc=1.870 Mg/m³; R=0.0428, R _w=0.0896 for 10296 reflections with I > 2σ(I). Sealed NMR tubes containing clusters 2 and 3 were found to be exceeding stable towards near-UV light and temperatures up to ca. 125 °C. The surprisingly robust behavior of 2 and 3 is contrasted with the related cluster Ru₃(CO)₁₀(bpcd) that undergoes fragmentation to the donor-acceptor compound Ru₂(CO)₆(bpcd) and the phosphido-bridged compound Ru₂(CO)₆(μ–PPh₂)[μ–C–C(PPh₂)C(O)CH₂C(O)] under mild conditions. The electrochemical properties of each substituted cluster have been investigated by cyclic voltammetry, and our findings are discussed with respect to the reported electrochemical data on the parent cluster H₄Ru₄(CO)₁₂.

Supramolecular Association in the Structure of 2,9-<Emphasis Type="Italic">C</Emphasis>-<Emphasis Type="Italic">meso</Emphasis>-2,5,5,7,9,12,12,14-Octamethyl-1,8-diaza-4,11-diazoniacyclotetradecane as its Bis(nitrate) and Bis(acetate) Trihydrate

Abstract In the crystal structure of the nitrate salt, columns of di-cationic macrocycles, each disposed about a center of inversion, are interspersed by pairs of nitrate anions that form charged-assisted N–H···O hydrogen-bonding interactions, reinforced by C–H···O contacts. The topology of the resulting supramolecular architecture is that of a linear chain and these associate via further weak C–H···O contacts. In the structure of the acetate trihydrate, di-cationic macrocycles are circumscribed by 32-membered rings defined by O–H···O interactions, involving the acetate anions and solvent water molecules. Systematic variations in the geometric parameters in the molecular structures are correlated with the influence of intermolecular interactions. The nitrate crystallizes in the monoclinic space group P2₁/n with a = 8.3524(11) ?, b = 12.5497(16) ?, c = 11.1208(16) ?, β = 103.180(3)°, and Z = 2. The acetate trihydrate also crystallizes in the monoclinic space group P2₁/n with a = 9.6679(15) ?, b = 15.278(2) ?, c = 9.8376(18) ?, β = 106.068(5)°, and Z = 2. Index Abstract Supramolecular Association in the Structure of 2,9- C-meso -2,5,5,7,9,12,12,14-Octamethyl-1,8-diaza-4,11- diazoniacyclotetradecane as its Bis(nitrate) and Bis(acetate) Trihydrate Saroj K. S. Hazari, ⁽¹⁾ Tapashi G. Roy, ^(1)* Kanak K. Barua ⁽¹⁾ and Edward R. T. Tiekink ^(2)* A linear supramolecular chain stabilized by charge-assisted N–H···O hydrogen-bonding interactions is found in the nitrate salt. In the acetate trihydrate, di-cationic macrocycles are circumscribed by 32-membered rings constructed by O–H···O hydrogen-bonds. Supramolecular Association in the Structure of 2,9- C-meso -2,5,5,7,9,12,12,14-Octamethyl-1,8-diaza-4,11- diazoniacyclotetradecane as its Bis(nitrate) and Bis(acetate) Trihydrate Saroj K. S. Hazari, ⁽¹⁾ Tapashi G. Roy, ^(1)* Kanak K. Barua ⁽¹⁾ and Edward R. T. Tiekink ^{(2)* (1)}Department of Chemistry, University of Chittagong, Chittagong-4331, Bangladesh ⁽²⁾Department of Chemistry, The University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249-0698 Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Structure of the undecahydrodecaborate anion B10H

The crystal structures of [Ph ₃PCH₂ Naph]B₁₀H₁₁(I) and [Ph ₃PEt]₂B₁₀H₁₀ (II) are studied (110 K and room temperature, R = 0.0673 and 0.0609 for 4176 and 953 observed reflections in I and II, respectively). It is unambiguously determined that protonation of the B₁₀H ₁₀ ²⁻ anion proceeds at one of the faces of the apical belt and results mainly in a significant lengthening of the edges of the centered face [B_e-B_e, 1.948(4) Å; B_a-B_e, 1.770(5) Å and 1.787(5) Å]. __________ Translated from Kristallografiya, Vol. 49, No. 5, 2004, pp. 855–859. Original Russian Text Copyright ? 2004 by Polyakova, Mustyatsa, Zhizhin, Kuznetsov.     

Investigation of Trimetallic Ligand-Pillared Oxyfluorides: Ag2Cu(pzc)2MOxF6?x (M?=?Mo, Nb, and W)

Abstract  

Three new ligand-pillared hybrid solids, Ag₂Cu(pzc)₂MO _x F_6−x (I, M = Mo, x = 2; II, M = W, x = 2; III, M = Nb, x = 1) (pzc = pyrazine-2-carboxylate) were synthesized via hydrothermal reactions at 150 °C, and their structures were determined by single-crystal X-ray diffraction (P2₁/n (No. 14), Z = 2; a = 7.2302(1), 7.2124(2), 7.2715(2) ?; b = 7.9460(1), 7.9270(2), 7.98436(3) ?; c = 13.9173(2), 13.8959(4), 13.8226(5) ?, for I, II, and III, respectively). All three are isostructural and contain unusual trimetallic (Ag₂CuMO _x F_6−x )²⁺ layers that consist of [Ag₂O₂F₂] _n and [CuMO _x F_6−x ] _n chains that alternate within the layers. Each structure also contains [MO _x F_6−x ]²⁻ octahedra with fully disordered O/F positions and with an inversion center on the M ⁿ⁺ sites, i.e., Mo⁶⁺, W⁶⁺ and Nb⁵⁺. Magnetic susceptibility measurements can be fitted to the Curie–Weiss law with a Curie constant consistent with a single non-interacting Cu(II) (S = ?) site per formula unit. Thermogravimetric analyses indicate that these hybrid compounds are stable up to ~280 °C, with each exhibiting a single weight-loss step beginning at ~300 °C that corresponds to the loss of all pyrazine-2-carboxylate ligands and additional O/F atoms via oxidation of the ligand during its removal. UV–Vis diffuse reflectance measurements show that each exhibits an optical bandgap size of ~2.8 eV, and which electronic-structure calculations show arise from excitations between the Cu(II)-based valence orbitals and the M^5+/6+-based conduction band orbitals.     

Structure and magnetic properties of heterometallic coordination carboxylate polymers with cobalt and lithium atoms

Reactions between lithium pivalate and cobalt coordination polymers [Co₅(OH₂)(OH)(Piv)₉)L ¹)₄] _n (I) and [Co₂(OH₂)(Piv)₄(L ²)₂] _n (II), where Piv—is the pivalate anion, L ¹ is pyrazine, and L ² is pyrimidine, result in new heterometallic polymers {[Li₂Co₂(Piv)₆(L ¹)₂]₂ MeCN} _n (III), {[Li₂Co₂(Piv)₆(L ²)]_0.5 MeCN} _n (IV), and [Li₂Co₂(Piv)₆(L ²)₂] _n (V). The resulting compounds contain tetra-nuclear {Li₂Co₂(Piv)₆} fragments connected by neutral bridging ligands (pyrazine or pyrimidine) into layer structures. Crystal structures III–V are determined, and the magnetic properties of III and IV are studied.     

Electron‐phonon short‐range interactions mobility and p‐ to n‐type conversion in TlGaS2 crystals

The conductivity type conversion from p ‐ to n ‐type at a critical temperature of 315 K in TlGaS₂ crystals is observed through the Hall effect measurements in the temperature range of 200–350 K. The analysis of the temperature‐dependent electrical resistivity, Hall coefficient and carrier concentration data reveals the extrinsic type of conduction with donor impurity levels that behave as acceptor levels when are empty. The data analysis allowed the calculation of hole and electron effective masses of 0.36m ₀ and 0.23m ₀, respectively. In addition, the temperature‐dependent Hall mobility is found to decrease with temperature following a logarithmic slope of ∼1.6. The Hall mobility in the n ‐region is limited by the electron‐phonon short‐range interactions scattering with an electron‐phonon coupling constant of 0.21. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Assembly of Dipicolinic Acid by Alkali-Metal Cations

Abstract  

Different types of structures of hydrogen-bond assemblies derived from partially deprotonated dipicolinic acid (LH2) molecules having alkali metal cation such as sodium, potassium and cesium are structurally characterised. These self assembled complexes have general formula [M(LH)(LH2)(H₂O) _m ] _n xH₂O {m = 2, 3, n = 1, 2, n, and x = 0, 0.5 M = Na (1); K (2) and Cs(3)}. Sodium complex is a hepta-coordinate mononuclear complex; potassium complex is octa-coordinate complex with dinuclear K₂O₂ type of carboxylate core; whereas the cesium complex is nona-coordinate polymeric complex. All these complexes crystallises in Triclinic, P-1 space group. Sodium complex has a = 6.9003(4) ?; b = 11.1440(6)?; c = 11.2059(5)?; α = 85.695(4)o; β = 82.103(3)o; γ = 87.432(4)o and volume = 850.60(8) ?³ Z = 2; Potassium complex has a = 7.0937(4)?; b = 11.0034(5)?; c = 11.2732(6)?; α = 91.603(3)o; β = 96.088(3)o; γ = 97.207(4)o; volume = 867.29(8) ?³; Z = 1 and cesium complex has a = 7.1410(6)?; b = 11.0625(8)?; c = 12.0667(9)?; α = 96.849(4)o; β = 93.850(4)o; γ = 105.495(4)o; volume = 907.14(12) ?³; Z = 2.