New Examples for the Unexpected Stability of the 10π‐Electron Hückel Arene [Si6]10–

The compounds Ba₄Ag₂Si₆, Eu₄Ag₂Si₆, and Ca₄Ag₂Si₆, prepared from the elements at 1273 K (the components in inner corundum crucibles are enclosed in sealed quartz ampoules), are brittle semiconductors with silvery luster. They react slowly with acids liberating hydrogen. Ba₄Ag₂[Si₆] and Eu₄Ag₂[Si₆] crystallize like Ba₄Li₂[Si₆] (space group Fddd (No. 70); a = 8.613 Å, b = 14.927 Å, c = 19.639 Å, and a = 8.420 Å, b = 14.585 Å, c = 17.864 Å, respectively), whereas Ca₄Ag₂[Si₆] represents a new structure type (space group Fmmm (No. 69); a = 8.315 Å, b = 14.391 Å, c = 8.646 Å). The three compounds are Zintl phases with the formal charges M²⁺, Ag⁺ and [Si₆]^10–. The mean bond lengths d(Si–Si) = 2.335–2.381 Å in the 10π‐Hückel arene [Si₆]^10– as well as d(Ag–Si) = 2.464–2.595 Å vary with the size of the M²⁺ cations. The chemical bonding was analyzed in terms of the Electron Localization Function (ELF) and compared with the bonding in related systems (Ce₄Co₂Si₆).     

The Periodate‐Based Double Perovskites M2NaIO6 (M = Ca,Sr, and Ba)

The crystal structures of the M₂NaIO₆ series (M = Ca, Sr, Ba), prepared at 650 °C by ceramic methods, were determined from conventional laboratory X‐ray powder diffraction data. Synthesis and crystal growth were made by oxidizing I^– with O₂^(air) to I⁷⁺ followed by crystal growth in the presence of NaF as mineralizator, or by the reaction of the alkali‐metal periodate with the alkaline‐earth metal hydroxide. All three compounds are insoluble and stable in water. The barium compound crystallizes in the cubic space group Fm3m (no. 225) with lattice parameters of a = 8.3384(1) Å, whereas the strontium and calcium compounds crystallize in the monoclinic space group P2₁/c (no. 14) with a = 5.7600(1) Å, b = 5.7759(1) Å, c = 9.9742(1) Å, β = 125.362(1)° and a = 5.5376(1) Å, b = 5.7911(1) Å, c = 9.6055(1) Å, β = 124.300(1)°, respectively. The crystal structure consists of either symmetric (for Ba) or distorted (for Sr and Ca) perovskite superstructures. Ba₂NaIO₆ contains the first perfectly octahedral [IO₆]^5– unit reported. The compounds of the ortho‐periodates are stable up to 800 °C. Spectroscopic measurements as well as DFT calculations show a reasonable agreement between calculated and observed IR‐ and Raman‐active vibrations.     

LixNayBa14LiN6: New Representatives of the Subnitride Family

Three new metal‐rich phases, Li₄Na₁₁Ba₁₄LiN₆, Li₅Na₁₀Ba₁₄LiN₆ and Na₁₄Ba₁₄LiN₆ have been prepared and their crystal structure determined. According to single crystal and powder X‐ray diffraction data, all compounds crystallize with cubic unit cells (Li₄Na₁₁Ba₁₄LiN₆: , a = 17.874(2) Å, Z = 4, V = 5710(1) ų; Li₅Na₁₀Ba₁₄LiN₆: , a = 17.799(1) Å, Z = 4, V = 5638.7(6) ų; Na₁₄Ba₁₄LiN₆: , a = 17.7955(5) Å, Z = 4, V = 5635.6(2) Å). The last mentioned compound crystallizes in the Na₁₄Ba₁₄CaN₆ type, and both Li₄Na₁₁Ba₁₄LiN₆ and Li₅Na₁₀Ba₁₄LiN₆ have related structures. These compounds open a series of metal‐rich Ba nitrides, containing the new Ba₁₄LiN₆ cluster.     

K and Ba distribution in the structures of the clathrate compounds KxBa16−x(Ga,Sn)136 (x = 0.8, 4.4, and 12.9) and KxBa8−x(Ga,Sn)46 (x = 0.3)

Studies of the K–Ba–Ga–Sn system produced the clathrate compounds K_0.8(2)Ba_15.2(2)Ga_31.0(5)Sn_105.0(5) [a = 17.0178 (4) Å], K_4.3(3)Ba_11.7(3)Ga_27.4(4)Sn_108.6(4) [a = 17.0709 (6) Å] and K_12.9(2)Ba_3.1(2)Ga_19.5(4)Sn_116.5(4) [a = 17.1946 (8) Å], with the type‐II structure (cubic, space group Fdm), and K_7.7(1)Ba_0.3(1)Ga_8.3(4)Sn_37.7(4) [a = 11.9447 (4) Å], with the type‐I structure (cubic, space group Pmn). For the type‐II structures, only the smaller (Ga,Sn)₂₄ pentagonal dodecahedral cages are filled, while the (Ga,Sn)₂₈ hexakaidecahedral cages remain empty. The unit‐cell volume is directly correlated with the K:Ba ratio, since an increasing amount of monovalent K occupying the cages causes a decreasing substitution of the smaller Ga in the framework. All three formulae have an electron count that is in good agreement with the Zintl–Klemm rules. For the type‐I compound, all framework sites are occupied by a mixture of Ga and Sn atoms, with Ga showing a preference for Wyckoff site 6c. The (Ga,Sn)₂₀ pentagonal dodecahedral cages are occupied by statistically disordered K and Ba atoms, while the (Ga,Sn)₂₄ tetrakaidecahedral cages encapsulate only K atoms. Large anisotropic displacement parameters for K in the latter cages suggest an off‐centering of the guest atoms.     

Structural chemistry of Ba2CdS3, Ba2CdSe3, BaCdS2, BaCu2S2 and BaCu2Se2

The structures of all compounds were determined from three dimensional single crystal X-ray diffraction data and refined by least squares. Ba₂CdS₃ and Ba₂CdSe₃ are isostructural, Pnma, a = 8.9145(6)Å, b = 4.3356(2)Å, c = 17.2439(9)Å for the former compound and a = 9.2247Å, b = 4,4823(6)Å, c = 17.8706(11)Å for the latter, z = 4, R = 0.0751 and R = 0.0462, respectively. The compounds are isostructural with the previously reported Mn analogues and with K₂AgI₃. Cd ions are in tetrahedral environment and the tetrahedra form infinite linear chains by corner sharing. Ba ions are in 7-fold coordination in which 6 anions form a trigonal prism and 1 anion caps one of the rectangular faces. BaCdS₂, Pnma, a = 7.2781(3)Å, b = 4.1670(1)Å, c = 13.9189(6)Å, z = 4, R = 0.0685. Cd ions can be considered to have a triangular planar coordination with CdS distances of 2.47 and 2.53 Å (twice). Two additional S ions are at 2.89 and 3.22 Å to complete a triangular bipyramidal configuration. Ba is in 7-fold coordination with the anions forming a trigonal prism which is capped on one rectangular face. The compound is isostructural with BaCdO₂ and is related to the structure of BaMnS₂. BaCdSe₂ could not be prepared. BaCu₂S₂ and BaCu₂Se₂ are isostructural, Pnma, a = 9.3081(4)Å, b = 4.0612(3)Å, c = 10.4084(5)Å for the sulfide and a = 9.5944(6)Å, b = 4.2142(4)Å, c = 10.7748(8)Å for the selenide, z = 4, R = 0.0634 and 0.0373, respectively. Ba ions are in the usual 7-fold, capped hexagonal prism, coordination. However, 9 Cu ions also can be considered to form a trigonal prism with all rectangular faces capped, around Ba since the BaCu distances range from 3.24 to 3.54 Å for the sulfide and from 3.37 to 3.67 Å for the selenide. One of the Cu ions is in a very distorted tetrahedral environment and the second one is located in a more regular tetrahedral configuration of the anions. Two independent infinite chains of tetrahedra are present. They are formed by sharing of two adjacent edges of each tetrahedron and then these chains in turn are linked by corner sharing into a three-dimensional network of tetrahedra.     

ThSi2 Type Ytterbium Disilicide and its Analogues YbTxSi2–x (T = Cr,Fe, Co)

YbSi₂ and the derivatives YbT_xSi_2–x (T = Cr, Fe, Co) crystallizing in the α‐ThSi₂ structure type were obtained as single crystals from reactions run in liquid indium. All silicides were investigated by single‐crystal X‐ray diffraction, I4₁/amd space group and the lattice constants are: a = 3.9868(6) Å and c = 13.541(3) Å for YbSi₂, a = 4.0123(6) Å and c = 13.542(3) Å for YbCr_0.27Si_1.73, a = 4.0142(6) Å and c = 13.830(3) Å for YbCr_0.71Si_1.29, a = 4.0080(6) Å and c = 13.751(3) Å for YbFe_0.34Si_1.66, and a = 4.0036(6) Å, c = 13.707(3) Å for YbCo_0.21Si_1.79. YbSi₂ and YbT_xSi_2–x compounds are polar intermetallics with three‐dimensional Si and M (T+Si) polyanion sub‐networks, respectively, filled with ytterbium atoms. The degree of substitution of transition metal at the silicon site is signficant and leads to changes in the average bond lengths and bond angles substantially.     

Orthorhombic Inverse Perovskitic Ba3TtO (Tt = Ge,Si) as Zintl Phases

The isotypic title compounds are obtained in high yield from the reactions of Ba, BaO, and Ge (Si) in welded Ta containers slowly cooled from 1100 °C. The structure of Ba₃GeO was determined by single-crystal X-ray diffraction (orthorhombic symmetry; Pnma (No. 62); a = 7.591(1), b = 10.728(1), c = 7.551(1) Å; Z = 4; R = 0.058, R_w = 0.065 for 780 reflections (I > 3σ(I)) with 2θ_max = 60°)). The structure consists of slightly deformed OBa₆ octahedra that are tilted by £ 14° with respect to their positions in the ideal inverse perovskite structure. These distortions optimize eight of the original twelve equal Ba–Ge distances. The ideal cubic Ca₃SiO (a = 4.699(1) Å) has also been synthesized.     

The Crystal Structure of Ba2CuAlF9: a New Structure Type in Copper Fluoride Chemistry

Ba₂CuAlF₉ is monoclinic: a = 5.374(2) Å, b = 7.312(2) Å, c = 9.371(3) Å, β = 90.20(1)°, Z = 2, space group P2₁/c (n° 14). The crystal structure was solved from X-ray single crystal data using 1071 unique reflections (900 with F_o/σ(F_o) > 4, R factor = 0.075). It is built up from infinite isolated cis chains of [MF₆] mixed occupied fluorine octahedra sharing each, one edge and one vertex (M is randomly Cu or Al). An analogous kind of linkage was already observed for two other compounds from the ternary system BaF₂/CuF₂/AlF₃. Close structural relationships exist between the cationic subnetworks of γ-BaAlF₅ and Ba₂CuAlF₉.     

Synthese und Kristallstrukturen von α‐ und β‐Ba3(PS4)2 sowie von Ba3(PSe4)2

Synthesis and Crystal Structures of α‐, β‐Ba₃(PS₄)₂ and Ba₃(PSe₄)₂ Ba₃(PS₄)₂ and Ba₃(PSe₄)₂ were prepared by heating mixtures of the elements at 800 °C for 25 h. Both compounds were investigated by single crystal X‐ray methods. The thiophosphate is dimorphic and undergoes a displacive phase transition at about 75 °C. Both modifications crystallize in new structure types. In the room temperature phase (α‐Ba₃(PS₄)₂: P2₁/a; a = 11.649(3), b = 6.610(1), c = 17.299(2) Å, β = 90.26(3)°; Z = 4) three crystallographically independent Ba atoms are surrounded by ten sulfur atoms forming distorted polyhedra. The arrangement of the PS₄ tetrahedra, isolated from each other, is comparable with the formation of the SO₄^2? ions of β‐K₂SO₄. In β‐Ba₃(PS₄)₂ (C2/m; a = 11.597(2), b = 6.727(1), c = 8.704(2) Å; β = 90.00(3)°; Z = 2) the PS₄ tetrahedra are no more tilted along [001], but oriented parallel to each other inducing less distorted tetrahedra and polyhedra around the Ba atoms, respectively. Ba₃(PSe₄)₂ (P2₁/a; a = 12.282(2), b = 6.906(1), c = 18.061(4) Å; β = 90.23(3)°; Z = 4) is isotypic to α‐Ba₃(PS₄)₂ and no phase transition could be detected up to about 550 °C.     

Crystal chemistry of lithium in octahedrally coordinated structures. I. Synthesis of Ba8(Me6Li2)O24 (Me = Nb or Ta) and Ba10(W6Li4)O30. II. The tetragonal bronze phase in the system BaONb2O5Li2O

The preparation, single crystal growth, and crystallographic properties of a close-packed, eight-layer, hexagonal (a = 5.803 Å, c = 19.076 Å) modification having the stoichiometry Ba₈Nb₆Li₂O₂₄ and of a close-packed, ten-layer, hexagonal (a = 5.760 Å, c = 23.742 Å) phase with Ba₁₀W₆Li₄O₃₀ stoichiometry are discussed. The isostructural Ba₈Ta₆Li₄O₂₄ form of the eight-layer phase was also prepared (a = 5.802 Å, c = 19.085 Å). Proposed crystal structures involve the pairing of lithium and metal (Nb, Ta, or W) octahedra to yield face-sharing units. The relationship of this phenomenon to other known close-packed phases containing Li is demonstrated. An investigation of the Ba₈Nb₆Li₂O₂₄Ba₁₀W₆Li₄O₃₀ system is reported.A tetragonal bronze phase homogeneity region was delimited at 1200°C in the BaONb₂O₅Li₂O system. A new orthorhombic phase (a = 10.197 Å, b = 14.882 Å, c = 7.942 Å) was prepared with the stoichiometry Ba₄Li₂Nb₁₀O₃₀.     

Synthesis,Crystal Structure,and Magnetic Properties of (2,2′‐dipyridylamine)(X−) Copper(II) Complexes (X−: Cyanate,Dicyanamide, Acetate,Thiocyanato)

The synthesis, structure, and magnetic properties of four 2,2′‐dipyridylamine ligand (abbreviated as Hdpa) containing copper(II) complexes. There is one binuclear compound, which is [Cu₂(μ_1,1‐NCO)₂(NCO)₂(Hdpa)₂] ( 1 ), and three mononuclear compounds, which are [Cu{N(CN)₂}₂(Hdpa)₂] ( 2 ), [Cu(CH₃CO₂)(Hdpa)₂·N(CN)₂] ( 3 ), and [Cu(NCS)(Acac)] ( 4 ). Compounds 1 and 4 crystallize in the monoclinic system, space group P2(1)/c and Z = 4, with a = 8.2465(6) Å, b = 9.3059(7) Å, c = 16.0817(12) Å, β = 91.090(1)°, and V = 1233.90(16) ų for 1 and a = 7.6766(6) Å, b = 21.888(3) Å, c = 10.4678(12) Å, β = 90.301(2)°, and V= 1758.8(4) ų for 4 . Compounds 2 and 3 crystallize in the triclinic system, space group P‐1 and Z = 1, with a = 8.1140(3) Å, b = 8.2470(3) Å, c = 9.3120(4) Å, β = 102.2370(10)°, and V = 592.63(4) ų for 2 and a = 7.4780(2) Å, b = 12.5700(3) Å, c = 13.0450(3) Å, β = 96.351(2)°, and V = 1211.17(5) ų for 3 . Complex ( 1 ), the magnetic data was fitted by the Bleaney‐Bowers equation (1). A very good fit was derived with J = 23.96, Θ = ?1.5 (g = 1.97). Complex ( 1 ) shows the ferromagnetism. Complexes ( 2 ), ( 3 ) and ( 4 ) of have the it is the typical paramagnetic behavior of unpaired electrons. Under a low temperature around 25 K, complexes ( 2 ) and ( 3 ) show weak ferromagnetic behavior. They are the cause of hydrogen bonds.     

Crystal Structures of Chiral Ionophores: Bis(9,9′-spirobifluorene)-26-crown-4 and -32-crown-6

The X-ray crystal structures of bis(9,9′-spirobifluorene)-26-crown-4βbenzene solvate (monoclinic, a = 15.47 Å, b 11.265 Å, c = 15.220 Å, β = 91.54°, space group C2) and bis(9,9′-spirobifluorene)-32-crown-6·dichloromethane solvate (tetragonal, a = 20.958 Å, c = 11.779 Å, space group P4₁2₁2) are described. Both compounds act as enantioselective ionophores for α-aminoalcohols.     

The Metallic Zintl Phase Ba3Si4 – Synthesis,Crystal Structure,Chemical Bonding,and Physical Properties

The Zintl phase Ba₃Si₄ has been synthesized from the elements at 1273 K as a single phase. No homogeneity range has been found. The compound decomposes peritectically at 1307(5) K to BaSi₂ and melt. The butterfly‐shaped Si₄⁶⁻ Zintl anion in the crystal structure of Ba₃Si₄ (Pearson symbol tP28, space group P4₂/mnm, a = 8.5233(3) Å, c = 11.8322(6) Å) shows only slightly different Si‐Si bond lengths of d(Si–Si) = 2.4183(6) Å (1×) and 2.4254(3) Å (4×). The compound is diamagnetic with χ ≈ −50 × 10⁻⁶ cm³ mol⁻¹. DC resistivity measurements show a high electrical resistivity (ρ(300 K) ≈ 1.2 × 10⁻³ Ω m) with positive temperature gradient dρ/dT. The temperature dependence of the isotropic signal shift and the spin‐lattice relaxation times in ²⁹Si NMR spectroscopy confirms the metallic behavior. The experimental results are in accordance with the calculated electronic band structure, which indicates a metal with a low density of states at the Fermi level. The electron localization function (ELF) is used for analysis of chemical bonding. The reaction of solid Ba₃Si₄ with gaseous HCl leads to the oxidation of the Si₄⁶⁻ Zintl anion and yields nanoporous silicon.     

Synthesis,Crystal Structures,and Characterization of Two 3d‐3d Heterometallic Coordination Frameworks: [ZnCo(Hcit)Cl] and [ZnCo(Hcit)Br]

Reactions between CoO, ZnCl₂ (or ZnBr₂), and molten citric acid (Hcit) led to the formation of two 3d‐3d heterometallic coordination frameworks: [ZnCo(Hcit)Cl] ( 1 ) and [ZnCo(Hcit)Br] ( 2 ). X‐ray structure analyses show that both compounds 1 and 2 crystallize in the monoclinic space group P2₁/n [ 1 : a = 5.8699(5) Å, b = 17.7963(13) Å, c = 9.2152(8) Å, β = 106.806(4) °, Z = 4, V = 921.53(13) Å³; 2 : a = 5.909(3) Å, b = 17.798(8) Å, c = 9.302(5) Å, β = 106.374(7) °, Z = 4, V = 938.6(8) Å³]. The structures of the two compounds are almost the same except for the terminal halogen ligand. Both of them are 3D frameworks based on citric acid bridging ligands and a 1D backbone chain built of corner‐shared {CoO₆} and {ZnO₃Cl} polyhedra. Photoluminescence and thermal stabilities of the compounds were studied.     

Neue Hexachalcogeno‐Hypodiphosphate der Erdalkalimetalle und des Europiums

New Hexachalcogeno‐Hypodiphosphates of Alkaline‐Earth Metals and Europium Six hexathio‐ and hexaseleno‐hypodiphosphates respectively with the formula M₂P₂X₆ (M = Ca, Sr, Eu, Ba; X = S, Se) were prepared by heating the elements at 750 °C (60 h) and their crystal structures were determined by single crystal X‐ray methods. Eu₂P₂S₆ (a = 9.396(2), b = 7.531(2), c = 6.593(2) Å, β = 91.48(2) °), Ba₂P₂S₆ (a = 9.966(1), b = 7.580(2), c = 6.737(2) Å, β = 91.17(3) °), Ca₂P₂Se₆ (a = 9.664(2), b = 7.519(2), c = 6.859(1) Å, β = 92.02(3) °), Sr₂P₂Se₆ (a = 9.844(2), b = 7.788(2), c = 6.963(1) Å, β = 91.50(3) °), Eu₂P₂Se₆ (a = 9.779(2), b = 7.793(2), c = 6.957(1) Å, β = 91.29(3) °), and Ba₂P₂Se₆ (a = 10.355(2), b = 7.862(2), c = 7.046(1) Å, β = 90.83(3) °) are isotypic and crystallize in the high temperature form of Sn₂P₂S₆ (P2₁/n; Z = 2). The discrete ethanlike (P₂X₆)^4— anions in staggered conformation are linked via X—M—X bonds to a three‐dimensional structure and in the course of this Ca²⁺, Sr²⁺, and Eu²⁺ are coordinated by 8 and Ba²⁺ by 8+1 S and Se atoms respectively. Susceptibility measurements of Eu₂P₂S₆ from 2 K to room temperature show Curie‐Weiss behavior with an experimental magnetic moment of 7.43(2) μ_B/Eu. No magnetic ordering was observed down to 2 K. A ¹⁵¹Eu Mössbauer spectrum at 77 K shows only one signal at an isomer shift of δ = —12.6(1) mm/s. The europium atoms in Eu₂P₂S₆ are therefore in a stable divalent oxidation state.     

Syntheses and Crystal Structures of the Novel Ternary Thioborates Na3BS3, K3BS3, and Rb3BS3

The orthothioborates Na₃BS₃, K₃BS₃ and Rb₃BS₃ were prepared from the metal sulfides, amorphous boron and sulfur in solid state reactions at temperatures between 923 and 973 K. In a systematic study on the structural cation influence on this type of ternary compounds, the crystal structures were determined by single crystal X‐ray diffraction experiments. Na₃BS₃ crystallizes in the monoclinic space group C2/c (No. 15) with a = 11.853(14) Å, b = 6.664(10) Å, c = 8.406(10) Å, β = 118.18(2)° and Z = 4. K₃BS₃ and Rb₃BS₃ are monoclinic, space group P2₁/c (No. 14) with a = 10.061(3) Å, b = 6.210(2) Å, c = 12.538(3) Å, β = 112.97(2) and a = 10.215(3) Å, b = 6.407(1) Å, c = 13.069(6) Å, β = 103.64(5)°, Z = 4. The potassium and rubidium compounds are not isotypic. All three compounds contain isolated [BS₃]^3– anions with boron in a trigonal‐planar coordination. The sodium cations in Na₃BS₃ are located between layers of orthothioborate anions, in the case of K₃BS₃ and Rb₃BS₃ stacks of [BS₃]^3– entities are connected via the corresponding cations. X‐ray powder patterns were measured and compared to calculated ones obtained from single crystal X‐ray structure determinations.     

Crystal Structures of rac-Methyl- (3R*, 3aS*, 4R*, 7R*, 7aR*)-7-Acetoxymethyl)-3-benzyl-4,5-dimethyl-1-oxo-3a,4,7,7a-tetrahydroisoindoline-7a-carboxylate

The X-ray structures of the compounds 4 and 2 have been determined by direct methods and refined by least squares techniques. Crystals of C₂₂H₂₇NO₅ and C₂₇H₂₇NO₅ are triclinic, space groups Pī with lattice parameters a = 13.652 (5) Å, b = 10.926 (3) Å, c = 7.755 (2) Å, a = 111.554 (4) Å, β = 85.541 (3) Å, γ = 104.813 (4) Å, and a = 15.394 (4) Å, b = 9.674 (3) Å, c = 8.522 (3) Å, a = 111.04 (4) Å, ß = 93.65 (4) Å, γ = 95.01 (4) Å, respectively.     

Synthesis,Crystal Structure,Bonding, and Properties of (Ba6O)(OsN3)2

The new barium nitridoosmate oxide (Ba₆O)(OsN₃)₂ was prepared by reacting elemental barium and osmium (3:1) in nitrogen at 815–830 °C. The crystal structure of (Ba₆O)(OsN₃)₂ as determined by laboratory powder X‐ray diffraction ( , No 148: a=b=8.112(1) Å, c=17.390(1) Å, V=991.0(1) ų, Z=3), consists of sheets of trigonal OsN₃ units and trigonal‐antiprismatic Ba₆O groups, and is structurally related to the “313 nitrides” AE₃MN₃ (AE=Ca, Sr, Ba, M=V–Co, Ga). Density functional calculations, using a hybrid functional, likewise indicate the existence of oxygen in the Ba₆ polyhedra. The oxidation state 4+ of osmium is confirmed, both by the calculations and by XPS measurements. The bonding properties of the OsN₃^5? units are analyzed and compared to the Raman spectrum. The compound is paramagnetic from room temperature down to T=10 K. Between room temperature and 100 K it obeys the Curie–Weiss law (μ=1.68 μ_B). (Ba₆O)(OsN₃)₂ is semiconducting with a good electronic conductivity at room temperature (8.74×10^?2 Ω^?1 cm^?1). Below 142 K the temperature dependence of the conductivity resembles that of a variable‐range hopping mechanism.     

Structural chemistry of Sr3Cr2WO9, Ca3Cr2WO9, and Ba3Cr2WO9

We have studied the preparation and crystallographic structure of three perovskite-type compounds: Sr₃Cr₂WO₉, cubic, the lattice parameter of which is a = 7.812Å; Ca₃Cr₂WO₉, tetragonal, the lattice parameters of which are a = 5.408 Å and c = 7.635Å; and Ba₃Cr₂WO₉, hexagonal, the lattice parameters of which are a = 5.691 Å and c = 13.957Å. We have compared these three structures and shown the relationship between the dimensions of the alkaline-earth metal and the existence of the different structures.     

Crystal Structure Determination of Tetrabarium‐digalliumoxide,Ba4Ga2O7

Single crystals of a new barium oxogallate were obtained by growth from a melt at 1500 °C. The compound is monoclinic, with cell parameters a = 17.7447(10) Å, b = 10.6719(5) Å, c = 7.2828(5) Å, β = 98.962(7)°, V = 1362.3(2) ų. The diffraction pattern shows systematic absences corresponding to the space group P12₁/c1. The structure was solved by direct methods followed by Fourier syntheses, and refined using a single crystal diffraction data set (R1 = 0.032 for 2173 reflections with I > 2σ(I)). The chemical composition derived from structure solution is Ba₄Ga₂O₇, with a unit cell content of Z = 6. Main building units of the structure are GaO₄ tetrahedra sharing one oxygen atom to form Ga₂O₇ groups. The Ga–O–Ga bridging angle of one of the two symmetrically independent groups is linear by symmetry. The dimers are crosslinked by barium cations coordinated by six to eight oxygen ligands.