Crystal Structures of NbOI3 and NbOBr3 – Polar Double Chains in Different Non‐centrosymmetric Structures

NbOI₃ was obtained from a reaction of Nb₂O₅, Nb, and I₂. Single crystals free from disorder were a by‐product from a reaction with additional CsI. The monoclinic crystal structure (C2, a = 14.624(3) Å, b = 3.9905(8) Å, c = 12.602(3) Å, β = 120.4(3)°, Z = 4, R₁(F) = 0.0368, wR₂(F²) = 0.0804) represents a new structure type which is built up by distorted octahedral NbI₄O₂ with unequal O‐atoms in trans‐position. The octahedra are linked to dimers by a common edge of iodine atoms and to double chains by the apical oxygen atoms. A non‐centrosymmetric structure results because the short Nb–O distances point to the same direction and the polar double chains are parallel. The crystal structure of NbOBr₃ (NbOCl₃‐type, , a = 11.635(6) Å, c = 3.953(2) Å, R₁(F) = 0.082, wR₂(F²) = 0.174) shows the same polar double chains but the dimeric units Nb₂Br₆O₂ are orthogonal.     

Synthesis,Structure, and Properties of LiNb6Cl15

Black single crystals of LiNb₆Cl₁₅ were obtained from reactions of Nb powder, NbCl₅ and LiCl in sealed niobium tubes at 850°C. The heavy atom structure of LiNb₆Cl₁₅ (Ia3 d (no. 230), Z = 16, a = 2055.5(2) pm at 100 K, R(F) = 0.028, R(F²) = 0.053) is isotypic with the structure of Ta₆Cl₁₅. The [Nb₆Cl₁₂]²⁺ clusters in the structure are three-dimensionally interconnected via three additional Cl^a?a. These bridge all vertices of niobium clusters, consistent with [Nb₆Cl₁₂ⁱCl]^? (the Nb? Cl^a–a? Nb angles are 140°). At low temperatures the lithium ions are disordered over one-third of sites (48 f), occupying cavities inside of two distorted corner-sharing tetrahedra of chloride. These positions for lithium represent the narrowest sections of infinite channels in the structure built up by chloride. An increased lithium ion mobility is obtained above 170 K by ⁷Li-NMR measurements.     

Nb2Y2X6, a Novel Type of NbIV Compounds with Cross-linked Nb2 and Y2 Dumbbells (Y = Se,Te; X = Br,I)

The compounds Nb₂Se₂Br₆, Nb₂Te₂Br₆, and Nb₂Te₂I₆ were prepared from the elements in sealed quartz ampoulès at 1073 K. The crystalline solids, exhibiting a metallic lustre, are insensitive against moisture and oxygen. All compounds undergo several reversible thermal transitions with temperature (DTA). Beside binary halides only NbYX₃ is present in the gas phase. The structures consist of one-dimensional infinite chains of halogen bridged Nb₂(Y₂)X₄ units containing single side-on bonded Nb₂ and Y₂ dumbbells forming a quasi tetrahedral Nb₂Y₂ cluster (Nb? Nb ? 283.2; 287.5; 293.2 pm; Se? Se ? 230.5 pm; Te? Te ? 267.0; 268.5 pm). The structural and magnetic properties clearly prove the formal oxidation states Nb⁴⁺ and Y^1?, unexpected from stoichiometry. (Structural data: all P2/a (No. 13); Nb₂Se₂Br₆: a = 1254.0(12); b = 689.7(10); c = 662.4(10) pm; β = 98.9(1)°; Z = 2; 1274 hkl; R = 0.066. Nb₂Te₂Br₆: a = 1259.7(13); b = 713.5(9); c = 667.0(9) pm; β = 97.6(1)°; 1557 hkl; R = 0.043. Nb₂Te₂I₆: a = 1347.3(3); b = 742.9(2); c = 714.1(2) pm; β = 98.52(2)°; 1540 hkl; R = 0.026).     

Crystal Structure of NbOBr2

Black, needle shaped crystals of NbOBr₂ were formed by reduction of NbOBr₃ with InBr at 500 °C. It crystallizes isotypically to NbOI₂ (monoclinic, space group C2, a = 13.833(4), b = 3.9079(6), c = 7.023(2) Å, β = 105.026(10)°). The structure consists of NbO₂Br₄ octahedra, which are connected to layers . Nb atoms of edge sharing octahedra form Nb₂ pairs with Nb–Nb distances of 3.144(5) Å. Within corner‐sharing octahedra alternating long and short Nb–O bonds are present, causing the polarity of the structure.     

CuClSe1.53Te0.47 and CuClSe0.56Te1.44: Structural and Vibrational Spectroscopic Investigations on Copper(I) Chalcogen Chlorides

CuClSe_1.53Te_0.47 and CuClSe_0.56Te_1.44 are obtained from the reaction of CuCl, Se, and Te in stoichiometric amounts. Both copper(I) selenium tellurium chlorides are monoclinic, space group P2₁/n (no. 14) with lattice constants of a = 7.837(1) Å, b = 4.699(1) Å, c = 10.762(2) Å, β = 104.37(2)°, V = 383.9(1) ų (CuClSe_1.53Te_0.47), and a = 8.074(1) Å, b = 4.830(1) Å, c = 10.973(1) Å, β = 103.87(2)°, V = 415.5(1) ų (CuClSe_0.56Te_1.44), and Z = 4. A common feature of these isostructural compounds are heteroatomic strands [YY'] (Y, Y' = chalcogen). These strands are running along [010] and are connected to layers by chains [CuCl]. Vibrational spectra of CuClSe_1.53Te_0.47, CuClSe_0.56Te_1.44, CuXTe₂ and CuX'Se₂ (X = Cl, Br, I; X' = Cl, Br) are analysed with respect to the bonding relations of the chalcogen chains. Modes derived from IR and Raman spectra are assigned by correlation with tri gonal Se and related copper(I) chalcogen halides. Both, X‐ray structural data and an analysis of the chalcogen vibrational modes in IR and Raman spectra, lead to a detailed insight into the ordering phenomena of the chalcogen chains in this type of copper(I) chalcogen halides.     

Synthesis and Structure of [Sn4Se11]6–, [Sn2Se52–], and [Sn3Se72–] – Model Anions for the Solventothermal Reaction Pathway to Lamellar Selenidostannates(IV)

Reaction of A₂CO₃ (A = K, Rb) with Sn and Se in an H₂O/CH₃OH mixture at 115–130°C affords the isotypic selenidostannates(IV) A₆Sn₄Se₁₁ _. xH₂O (A = K, x = 8) 1 and 2 whose discrete [Sn₄Se₁₁]^6– anions each contain two corner‐bridged ditetrahedral [Sn₂Se₆]^4– species. Similar reaction conditions with A = Cs afford Cs₂Sn₂Se₅ _. H₂O ( 3a ) and Cs₂Sn₂Se₅ ( 3b ) in which such [Sn₂Se₆]^4– building blocks are connected through common Se atoms into infinite [Sn₂Se₅^2–] chains. The [Sn₃Se₇^2–] ribbons of (Et₄N)₂Sn₃Se₇ ( 4 ), formed by treating (Et₄N)I with Sn and Se in methanol at 130°C, can be regarded as resulting from the condensation of [Sn₂Se₅^2–] chains with molecular [SnSe₄]^4– anions. The anions [Sn₄Se₁₁]^6–, [Sn₂Se₅^2–], and [Sn₃Se₇^2–] represent the products of individual reaction steps on the potential condensation pathway of [Sn₂Se₆]^4– to the lamellar selenidostannates(IV) [Sn₄Se₉^2–] or [Sn₃Se₇^2–].     

Darstellung,Kristallstruktur und Schwingungsspektren von (n-Bu4N)2[(Mo6I)(NCS)]

Synthesis, Crystal Structure, and Vibrational Spectra of (n-Bu₄N)₂[(Mo₆I)(NCS)] By treatment of [(Mo₆I)I]^2– with (SCN)₂ in dichloromethane at –20 °C the hexaisothiocyanato cluster anion [(Mo₆I)(NCS)]^2– is formed. The X-ray structure determination of (n-Bu₄N)₂[(Mo₆I)(NCS)] · 2 Me₂CO (monoclinic, space group P2₁/c, a = 13.168(5), b = 11.964(5), c = 24.636(5) Å, β = 104.960(5)°, Z = 2) shows, that the thiocyanate groups are coordinated exclusively via N atoms with Mo–N bond lengths of 2.141–2.150 Å, Mo–N–C angles of 166–178° and N–C–S-angles of 174–180°. The vibrational spectra exhibit characteristic innerligand vibrations at 2073–2054 (ν_CN), 846–844 (ν_CS) and 480–462 cm^–1 (δ_NCS).     

Trennung und Charakterisierung der metallgemischten Cluster [(Nbn Ta6–n) Cl]2+, n = 0–6

Separation and Characterization of Mixed-Metal Clusters [(Nb_n Ta_6–n)Cl ]²⁺, n = 0–6 By reaction of NbCl₅ with Ta or TaCl₅ with Nb in fused NaCl the mixed-metal compounds [(Nb_nTa_6–n)Cl]²⁺, n = 0–6, are obtained. The anions formed in NaF solution by coordination of F^?? are kinetically stable at lower temperatur (–5°C). They have been separated by repeated ion exchange chromatography on DEAE cellulose to give the mixed-metal clusters, for n = 1 and 5 as pure compounds, for n = 2, 3, 4 as pairs of geometric isomers according to statistical distribution. The clusters are distinguishable by intense charge transfer bands shifting on metal substitution by steps of about 12 nm from 327 (Ta₆) to 396 nm (Nb₆). The IR spectra (80 K) exhibit only in the region of the antisymmetric metal–metal vibration distinct band patterns, which are assigned to the components of the degenerated T_1u vibration of the octahedral homonuclear clusters at 233 (Nb₆) and 209 cm^?1 (Ta₆), due to the lower symmetry D_4h, C_4v, and C_2v of the mixed-metal clusters. Along with the substitution of Nb by Ta the metal-Clⁱ vibrations are systematically shifted to lower frequencies, whereas all deformation modes remain uninfluenced.     

A New Structure Type for Rare-Earth-Metal Cluster Compounds stabilized by transition metals: KPr6I10Os,CsPr6I10Fe,CsLa6I10Fe,and CsLa6I10Mn

Reactions of KI, Pr, PrI₃, and Os in niobium tubes at 800° yielded black, air- and moisture-sensitive crystals of Kpr₆I₁₀Os which were characterized by single crystal X-ray diffraction (orthorhombic, Pnma, a = 15.362(3), b = 13.498(2), c = 14.128(3) Å, Z = 4, R(F)/R_w = 4.4/5.6%). Subsequent parallel experiments also gave, according to Guinier powder pattern data, the isostructural compounds CsPr₆I₁₀Fe (a = 15.312(2), b = 13.426(1), c = 14.154(1) Å), CsLa₆I₁₀Fe (a = 15.523(2), b = 13.646(2), c = 14.334(1) Å) and CsLa₆I₁₀Mn (a = 15.457(4), b = 13.737(2), c = 14.329(2) Å). The important structural feature is the presence of octahedral rare-earth-metal cluster units R₆ that are centered by a transition-metal atom Z and bridged and interconnected by halide atoms. The new compounds exhibit the same general pattern of halide connectivity (R₆Z)XXXX as do the triclinic compounds R₆X₁₀Z. However, the structural arrangement of the metal octahedra is significantly different; they are linked by I^i–i atoms into zigzag chains along [010] and these are interconnected into a three dimensional network by I^i–a atoms to form channels in which the alkali-metal atoms are located. The introduction of alkali-metal atoms into reactions leads to new quaternary compounds with discrete rare-earth-metal clusters centered by transition metals and more open structure frameworks. Measurements of the temperature dependencies of the magnetic susceptibilities for CsLa₆I₁₀Fe and CsLa₆I₁₀Mn are consistent with expectations for 17- and 16-electron cluster systems, respectively.     

Crystal Structures of {[Cd(phen)](C6H8O4)3/3} and {[Cd(phen)](C7H10O4)3/3} · 2H2O with C6H10O4 = Adipic Acid and C7H12O4 = Pimelic Acid

Two coordination polymers {[Cd(phen)](C₆H₈O₄)_3/3} ( 1 ) and {[Cd(phen)](C₇H₁₀O₄)_3/3} · 2H₂O ( 2 ) were structurally characterized by single crystal X‐ray diffraction methods. In 1 (C2/c (no. 15), a = 16.169(2)Å, b = 15.485(2)Å, c = 14.044(2)Å, β = 112.701(8)°, U = 3243.9(7)ų, Z = 8), the Cd atoms are coordinated by two N atoms of one phen ligand and five O atoms of three adipato ligands to form mono‐capped trigonal prisms with d(Cd‐O) = 2.271‐2.583Å and d(Cd‐N) = 2.309, 2.390Å. The [Cd(phen)] moieties are bridged by adipato ligands to generate {[Cd(phen)](C₆H₈O₄)_3/3} chains, which, via interchain π—π stacking interactions, are assembled into layers. Complex 2 (P1¯(no. 2), a = 9.986(1)Å, b = 10.230(3)Å, c = 11.243(1)Å, α = 66.06(1)°, β = 87.20(1)°, γ = 66.71(1)°, U = 955.7(2)ų, Z = 2) consists of {[Cd(phen)](C₇H₁₀O₄)_3/3} chains and hydrogen bonded H₂O molecules. The Cd atoms are pentagonal bipyramidally coordinated by two N atoms of one phen ligand and five O atoms of three pimelato ligands with d(Cd‐O) = 2.213—2.721Å and d(Cd‐N) = 2.329, 2.372Å. Through interchain π—π stacking interactions, the {[Cd(phen)](C₇H₁₀O₄)_3/3} chains resulting from [Cd(phen)] moieties bridged by pimelato ligands are assembled in to layers, between which the hydrogen bonded H₂O molecules are sandwiched.     

Electrochemical behavior of NbV–EDTA and NbV–citrate systems in aqueous solutions

The electrochemical reduction of Nb^V using oxalatoniobic acid and ammonium oxooxalatoniobate salts was studied in aqueous solutions of citric acid and sodium ethylenediaminetetraacetate (EDTA), in a wide range of supporting electrolyte concentrations and pH. In EDTA two reduction processes were observed: Nb^V to Nb^IV, E = −1.000 V vs. Ag/AgCl at pH 4.50 and Nb^IV to Nb^IIIE = −1.400 V vs. Ag/AgCl (pH 4.50). In citric acid there was only one reduction process: (Nb^V to Nb^IV), E = −1.260 V vs. Ag/AgCl at pH 4.50. In both electrolytes a linear relationship was found between the diffusion current and the niobium concentration in the 1.0 × 10⁻⁵ to 5.0 × 10⁻³ M range. Using cyclic voltammetry, it waa observed that the charge transfer process in the Nb^V to Nb^IV process is reversible in EDTA and reversible–quasireversible in citric acid.     

CuBrSe2: a Metastable Compound in the System CuBr / Se

Metastable CuBrSe₂ was prepared by the fast cooling of a melt (T ≥ 400°C) of copper(I) bromide and selenium in the ratio 1:2 to room temperature. The crystal structure was determined from single crystals separated from the solidified melt. The compound crystallizes isotypic to CuXTe₂ (X = Cl, Br, I) and CuClSe₂, space group P2₁/n (No. 14) with a = 7.8838(9) Å, b = 4.6439(4) Å, c = 11.183(1) Å, β = 103.44(1)°, V = 398.2(1) ų, and Z = 4. The refinement converged to R = 0.0424 and wR = 0.0851 (all reflections), respectively. In the crystal structure formally neutral one‐dimensional selenium chains [Se] are coordinated to copper(I) bromide. Slow cooling of the melt or heating of solid CuBrSe₂ to 250°C for some hours results in the decomposition of the compound, and a mixture of CuBrSe₃ and CuBr is formed. DSC measurements indicate, that this decomposition starts at about 200°C. Nevertheless, a melting point of 342°C can be determined. In Raman spectra of CuBrSe₂, selenium‐selenium stretching modes are found at ν_Se–Se = 241 and 219 cm^–1.     

Laser desorption ionization time‐of‐flight mass spectrometric study of binary As‐Se glasses

Binary chalcogenide As‐Se glasses and their thin films are important for optics, computers, materials science and technological applications. To increase understanding of the properties of thin films fabricated by plasma deposition techniques, more information concerning the physics of plasma plume is needed. In this study the formation of clusters in plasma plume from different As‐Se glasses by laser desorption ionization (LDI) or laser ablation (LA) was studied by time‐of‐flight mass spectrometry (TOF MS) in positive and negative ion modes. Formation of a number of As_pSe_q singly charged clusters As₃Se (q = 1–5), AsSe (q = 1–3), As₂Se (q = 2–4), and As₃Se (q = 2–5) was found from As‐Se glasses with the molar ratio As:Se in the range from 1:2 to 7:3. The stoichiometry of the As_pSe_q clusters was determined via isotopic envelope analysis and computer modeling. The structure of the clusters is proposed and the relationship to the structure of the parent glasses, as also suggested by Raman scattering spectra, is discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXVI. Ba12Ba2 2/3M 1/3□2O33□3 (MV = Nb,Ta) – die ersten Stapelvarianten eines rhomboedrischen 36 L-Typs

On Hexagonal Perovskites with Cationic Vacancies. XXVI. Ba₁₂Ba_{2 2/3}M _1/3□₂O₃₃□₃ (M^V = Nb, Ta) – the First Stacking Polytypes of a Rhombohedral 36 L-Type In the systems BaO? MO₅(M^V = Nb, Ta) for a Ba:M^V ratio of 2:1 polymorphism is observed. Here the low temperature modifications are described. They crystallize in a rhombohedral 36 L structure with three formula units Ba₁₂Ba_{2 2/3}M _1/3□₂O₃₃□₃ for the trigonal setting (M^V = Nb: a = 5.92₂ Å; c = 93.₂₅ Å; Ta: a = 5,92₂ Å; s = 93.4 Å).     

Synthesis and Crystal Structure of Bis(tetraphenylphosphonium) Hexabromo‐diselenate(II)‐bis{dibromodiselenate(I)}, [PPh4]2[Se2Br6(Se2Br2)2], the Salt of a Mixed‐valence Bromoselenate(II,I) Anion

The Red crystals of [PPh₄]₂[Se₂Br₆(Se₂Br₂)₂] ( 1 ) were obtained when selenium and bromine reacted in the solution of acetonitrile in the presence of tetraphenylphosphonium bromide. The crystal structure of 1 has been determined by X‐ray diffraction and refined to R = 0.0201 for 4024 reflections. The crystals are triclinic, space group with Z = 2 and a = 11.2757(4) Å, b = 12.3347(5) Å, c = 12.4948(5) Å, α = 113.152(4)°, β = 114.745(4)°, γ = 91.208(3)° (120(2) K). In the solid state the anion of 1 is built up of the Se₂Br₆ core and two Se₂Br₂ molecules each of which is linked to one of the trans‐positioned terminal Br_t atoms of the Se₂Br₆ core. The central Se₂Br₆ part consists of a nearly planar arrangement of two planar SeBr₄ units sharing a common edge through two μ₂‐bridging Br atoms. The contact between the Br_t and the Se^I atom of the Se₂Br₂ molecule is 3.0872(5) Å and can be interpreted as a bond of the donor‐acceptor type with the Br_t as donor and the Se₂Br₂ molecule as acceptor. The terminal Se^II–Br and μ₂Br–Se^II bond lengths are 2.3654(4), 2.6699(5) Å and 2.5482(5), 3.0265(5) Å, respectively. The bond lengths in the coordinated Se₂Br₂ molecule are: Se^I–Se^I = 2.2686(5) Å, Se^I–Br = 2.3779(5) and 2.3810(5) Å.     

Two Modifications of Copper(I) Octahedro-Hexatungsten(II) Tetradecabromide,Cu2[W6Br14]

The reaction of W₆Br₁₂ with CuBr sealed in an evacuated silica tube at the temperature gradient 925/915 K and annealing at 625/300 K yields a mixture of orthorhombic α-Cu₂[W₆Br₁₄] and cubic β-Cu₂[W₆Br₁₄] in the low temperature zone. α-Cu₂[W₆Br₁₄] crystallizes in the space group Pbca (no. 61), a = 15.126 Å, b = 9.887 Å, c = 15.954 Å, Z = 4, oP88, and β-Cu₂[W₆Br₁₄] crystallizes in the space group Pn3 (no. 201), a = 13.391 Å, Z = 4, cP88. The crystal structures are built up by [(W₆Br)Br]^2– cluster anions and Cu⁺ cations. The cluster anions show only in the peripheral shells small deviation from m3m symmetry (d(W–W) = 2.630 Å; d(W–Brⁱ) = 2.618 Å; d(W–Br^a) = 2.614 Å). The anions are arranged in a slightly compressed bcc pattern (α) and ccp (β) pattern, respectively. The Cu⁺ cations are trigonal-planar coordinated by Br^a ligands with d(Cu–Br) = 2.377 Å (α) and 2.378 Å (β). The cubic β-modification is diamagnetic with an unexpected large susceptibility (χ_mol = –884 × 10^–6 cm³ mol^–1) and have a band gap of 2.8 eV. It decomposes under dynamic vacuum in two steps at 795 K und 1040 K.     

Darstellung,Schwingungsspektren und Kristallstrukturen von [(Ph3P)2N]2[(W6Cl)I] · 2 Et2O · 2 CH2Cl2 und [(Ph3P)2N]2[(W6Cl)(NCS)] · 2 CH2Cl2

Synthesis, Crystal Structures, and Vibrational Spectra of [(Ph₃P)₂N]₂[(W₆Cl )I ] · 2 Et₂O · 2 CH₂Cl₂ and [(Ph₃P)₂N]₂[(W₆Cl )(NCS) ] · 2 CH₂Cl₂ By treatment of [(W₆Cl)I]^2– with (SCN)₂ in dichloromethane at –20 °C the hexaisothiocyanato cluster anion [(W₆Cl)(NCS)]^2– is formed. X‐ray structure determinations have been performed on single crystals of [(Ph₃P)₂N]₂[(W₆Cl)I] · 2 CH₂Cl₂ · 2 Et₂O ( 1 ) (triclinic, space group P1, a = 10.324(5), b = 14.908(3), c = 17.734(8) Å, α = 112.78(2)°, β = 99.13(3)°, γ = 92.02(3)°, Z = 1) and [(Ph₃P)₂N]₂[(W₆Cl)(NCS)] · 2 CH₂Cl₂ ( 2 ) (triclinic, space group P1, a = 11.115(2), b = 14.839(2), c = 17.036(3) Å, α = 104.46(1)°, β = 105.75(2)°, γ = 110.59(1)°, Z = 1). The thiocyanate ligands of 2 are bound exclusively via N atoms with W–N bond lengths of 2.091–2.107 Å, W–N–C angles of 173.1–176.9° and N–C–S angles of 178.1–179.3°. The vibrational spectra exhibit characteristic innerligand vibrations at 2067–2045 (ν_CN), 879–867 (ν_CS) and 490–482 (δ_NCS). Based on the molekular parameters of the X‐ray determination of 1 the vibrational spectra of the corresponding (n‐Bu₄N) salt of 1 are assigned by normal coordinate analysis. The valence force constants are f_d(WW) = 1.61, f_d(WI) = 1.23 and f_d(WCl) = 1.10 mdyn/Å.     

Darstellung und Kristallstruktur von trans-(Ph4As)2[OsCl2(NCS)(SCN)], Schwingungsspektren und Normalkoordinatenanalyse

Preparation and Crystal Structure of trans-(Ph₄As)₂[OsCl₂(NCS) (SCN) ], Vibrational Spectra and Normal Coordinate Analysis By treatment of trans-[OsCl₂I₄]^2? with (SCN)₂ in dichloromethane a mixture of different linkage isomers is formed, from which trans-[OsCl₂(NCS)(SCN)]^2? has been isolated by ion exchange chromatography on diethylaminoethyl cellulose. The X-Ray structure determination on a single crystal of trans-(Ph₄As)₂[OsCl₂(NCS)(SCN)] (triclinic, space group P 1 , a = 12.505(5), b = 12.056(5), c = 19.833(5) Å, α = 108.047(5)°, β = 91.964(5)°, γ = 117.048(5)°, Z = 2) reveals that two cis-positioned Thiocyanate(N) groups are coordinated with Os? N? C angles of 172.1° and 173.0° and two cis-positioned Thiocyanate(S) groups are coordinated with Os? S? C angles of 106.9° and 108.7°. Using the molecular parameters of the X-Ray determination the low temperature (10 K) IR and Raman spectra of the (n-Bu₄N) salt of the linkage isomer are assigned by a normal coordinate analysis based on a modified valence force field. The valence force constants are f_d(OsN) = 1.63 and f_d(OsS) = 1.30 mdyn/Å. Taking into account the trans influence a good agreement between observed and calculated frequencies is achieved.     

Darstellung,Eigenschaften, röntgenographische und spektroskopische Untersuchung von Tl4Nb2S11 und Tl4Ta2S11

On Polychalcogenides of Thallium with M₂Q₁₁ Groups as a Structural Building Block. I Preparation, Properties, X‐ray Diffractometry, and Spectroscopic Investigations of Tl₄Nb₂S₁₁ and Tl₄Ta₂S₁₁ The new ternary compounds Tl₄Nb₂S₁₁ and Tl₄Ta₂S₁₁ were prepared using Thallium polysulfide melts. Tl₄M₂S₁₁ crystallises isotypically to K₄Nb₂S_8.9Se_2.1 in the triclinic space group P 1 with a = 7.806(2) Å, b = 8.866(2) Å, c = 13.121(3) Å, α = 72.72(2)°, β = 88.80(3)°, and γ = 85.86(2)° for M = Nb and a = 7.837(1) Å, b = 8.902(1) Å, c = 13.176(1) Å, α = 72.69(1)°, β = 88.74(1)°, and γ = 85.67(1)° for M = Ta. The interatomic distances as well as angles within the [M₂S₁₁]^4– anions are similar to those of the previously reported data for analogous alkali metal polysulfides. Significant differences between Tl₄M₂S₁₁ and A₄M₂S₁₁ (A = K, Rb, Cs) are obvious for the shape of the polyhedra around the electropositive elements. The two title compounds melt congruently at 732 K (M = Nb) and 729 K (M = Ta). The optical band gaps were estimated as 1.26 eV for Tl₄Nb₂S₁₁ and as 1.80 eV for the Tantalum compound.     

The Mixed Valence Tungsten(IV,V) Compound Na[W2O2Br6]

The reaction of W₆Br₁₂, NaBr, and WO₂Br₂ in the presence of Br₂ in a sealed silica tube yields Na[W₂O₂Br₆] together with WOBr₄ and WO₂Br₂ in the low temperature zone (temperature gradient 1030/870 K). Na[W₂O₂Br₆] crystallizes orthorhombically in the space group Immm (no. 71) with a = 3.775 Å, b = 10.400 Å, c = 13.005 Å and Z = 2. Pairs of condensed trans-[WO₂Br₄] octahedra with a common Br₂ edge form along [100] double chains [W₂O_4/2Br₆]^1– via the oxygen atoms. The mixed valent tungsten atoms are bonded to W₂ pairs with a 2 c–3 e bond (d(W–W) = 2.946 Å, d(W–O) = 1.888 Å, d(W–Br^b) = 2.537 Å, d(W–Br^t) = 2.535 Å, ∢O–W–O = 177.4°, ∢Br^b–W–Br^b (endocyclic) = 109.0°). The Na⁺ cations connect the anionic double chains to form two-dimensional layers parallel (001), which interact by van der Waals forces. The cations are eightfold coordinated by a cube of the terminal Br^t ligands of the polymeric anions (d(Na–Br) = 3.138 Å). Na[W₂O₂Br₆] may be discussed as an intercalation compound of the oxide bromide WOBr₃.