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  • Author: Wolfgang Jeitschko x
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Abstract

The title compounds were prepared by solid state reaction of the elemental components. Their crystal structures were determined from single-crystal X-ray diffractometer data. Ag2SiP2: 14̄2d, a = 652.75(5) pm, c = 855.0(1) pm, Z = 4, R = 0.024 for 611 structure factors and 14 variable parameters; AuSiP: R3m, a = 345.9(1) pm, c = 1720.0(3) pm, Z = 3, R = 0.023 (352 F values, 11 variables). The silicon atoms in Ag2SiP2 are tetrahedrally coordinated by phosphorus atoms. The compound might therefore be considered as a phosphidosilicate and its formula can be rationalized as (Ag+1)2Si+4(P-3)2. However, Ag2SiP2 is not a tetrahedral compound since the phosphorus atoms have five near neighbors (3Ag + 2Si) and the silver atoms are coordinated by three phosphorus atoms in almost trigonal planar coordination. Weak silver-silver bonding is assumed for the shortest Ag-Ag contacts of 318 pm. In AuSiP the gold atoms are in a linear coordination of one silicon (235.5 pm) and one phosphorus atom (232.6 pm). The silicon and phosphorus atoms are tetrahedrally coordinated (3Si + 1 Au and 3P + 1 Au, respectively). Thus, the elements can be assigned oxidation numbers according to the formula Au+1Si+2P-3 . This structure was also refined in the centrosymmetric space group R3̄m, but in this improper setting the silicon and phosphorus atoms occupy one crystallographic site with random occupancy.

The new compounds GdRe2Al10 and TbRe2Al10 were obtained in well-crystallized form by reaction of the elemental components with an excess of aluminum after dissolving the matrix in hydrochloric acid. They crystallize with a new structure type which has been determined for TbRe2Al10 from single-crystal X-ray data: Cmcm, a = 932.2(1), b = 1030.4(1 ), c = 1803.2(3)pm, Z = 8, R = 0.031 for 1159 structure factors and 77 variable parameters. Of the two terbium sites, one does not have full occupancy with terbium, however, it may have mixed Tb/Al occupancy. The resulting compositions are Tb0.948(5)Re2Al10 or Tb0.936(3)Re2Al10.064(3), respectively. The terbium atoms are coordinated by 4 Re and 16 Al atoms. The rhenium atoms are situated in distorted icosahedra formed by 2 Tb and 10 Al atoms. The nine different aluminum atoms have between 12 and 14 neighbors (1 or 2 Tb, 2 Re, and between 8 and 11 Al atoms). The structure may be viewed as consisting of two kinds of alternating layers. One of these is puckered, hexagonal close packed, with a mesh content of 4ReAl3; the other is planar and less densely packed. It has the mesh content 2TbAl4. The same kinds of atomic layers have been found in the structures of YbFe2Al10 and LuRe2Al10. Thus, the three structure types may be considered as stacking variants of each other. The tetragonal CaCr2Al10 (ordered ThMn12) type structure also belongs to this structural family, although the CaAl4 layers somewhat differ from the layers TbAl4, YbAl4, and LuAl4.

The title compounds have been prepared by arc-melting cold-pressed pellets of the elemental components. They crystallize with a new structure type, which was determined from singlecrystal X-ray diffractometer data of Th2NiB10: Pbam, a = 564.6(2) pm, b = 1120.4(3) pm, c = 417.3(1) pm, Z = 2, R = 0.020 for 748 structure factors and 25 variable parameters. The structures of Th2FeB10 (a = 562.7(1) pm, b = 1126.1(3) pm, c = 418.3(2) pm) and Th2CoB10 (a = 562.4(1) pm, b = 1122.8(2) pm, c = 418.5(1) pm) were refined from single-crystal data to residuals of 0.025 (921 F values) and 0.032 (911 F values). The lattice of these ternary borides may be derived from that of ThB6 (Th2B12) with the cubic CaB6 type structure by replacing two of the linking boron atoms of adjacent B6 octahedra by a transition metal atom.

Well-crystallized samples of the rhenium aluminides Re4Al11 and ReAl6 were obtained by reaction of rhenium with an excess of aluminum. Re4Al11 was found to be isotypic with Mn4Al11. The MnAl6 type structure of ReAl6 was confirmed. The crystal structures of both compounds were refined from single-crystal X-ray data. Re4Al11:P1̄, Z = 1, a = 516.0(1) pm, b = 896.3(2) pm, c = 516.9(1) pm, a = 90.44(1)°, β = 99.76(1)°, γ = 105.17(1)°, V = 0.2271 nm3, R = 0.036 for 2315 structure factors and 74 variable parameters. ReAl6: Cmcm, Z = 4, a = 761.0(1) pm, b = 660.5(1) pm, c = 903.4(1) pm, V = 0.4541 nm3, R = 0.013 for 711F values and 23 variables. In both structures the rhenium atoms have ten aluminum neighbors at distances from 245 to 277 pm. The Al-Al distances cover the whole range from 251 to 362 pm rather continuously. The previously reported compound Re2Al with the tetragonal MoSi2-type structure has the lattice constants a = 298.1(1) pm, c = 958.4(4) pm, V = 0.08519 nm3. ReAl6 shows Pauli-paramagnetism.

The title compounds have been prepared by annealing cold-pressed pellets of the binary nitrides LnN and CrN. Well developed crystals were obtained by recrystallization of the binary or prereacted ternary nitrides in a Li3N flux. Their structures were determined from single-crystal diffractometer data. C e2CrN3 has a U2CrN3 type structure: Immm , a = 379.0(1), b = 340.4(1), c = 1251.7(2) pm, Z = 2, R = 0.012 for 383 structure factors and 16 variables. The atomic positions of this structure are similar to those of U2IrC2 and K2NiF4. The structure may be rationalized to a first approximation with the formula (Ce+4)2[CrN3]8−. The chromium atoms are in a distorted square-planar nitrogen coordination. The CrN4-squares are linked via corner-sharing nitrogen atoms, thus forming infinite, straight - N - CrN2- N - CrN2- chains. The cubic structure of La3Cr10−xN11 (a = 1298.2(1) pm ), Ce3Cr10−xN11 (with a small homogenity range; a = 1284.3(1)-1286.1(3) pm ), and Pr3Cr10−xN11 (a = 1289.1(2) pm ) was determined for the lanthanum compound: Fm 3̄ m , Z = 8, R = 0.027 for 189 F values and 18 variables. One chromium site was found to have an occupancy of only 80.9(5)% resulting in the composition La3Cr9.24(1)N11. The nitrogen atoms occupy four atomic sites. Three of these have octahedral environments (6 La, 3 La + 3 Cr, 2 La + 4 Cr), the fourth one is surrounded by eight chromium atoms forming a cube. The chromium atoms are tetrahedrally coordinated by nitrogen atoms, and these CrN4-tetrahedra are linked via common corners and edges to form a three-dimensionally infinite polyanionic network. In addition the chromium atoms with oxidation numbers of about 2 to 3 form numerous Cr - Cr bonds, which allow to rationalize the Pauli paramagnetism of the compound.

The title compounds were prepared by reaction of the elemental components. They crystallize in a new structure type, which was determined from single-crystal X -ray data of CeCrSb3: Pbcm, a = 1310.8(3), b = 618.4(1), c = 607.9(1) pm, Z = 4, R = 0.029 for 648 structure factors and 32 variable parameters. The structure of the antimonide CeVSb3 is isotypic: a = 1319.0(2), b = 623.92(8), c = 603.03(8) pm , R = 0.041 for 477 structure factors and 32 variables. The transition metal site and one of the three antimony sites were found to have partial occupancies resulting in the exact compositions CeV0,91(1)Sb2,916(4) and CeCr0,901(9)Sb2,909(4). The structures contain fractional Sb -Sb bonds with distances varying between 301,5 and 316.4 pm. The transition metal atoms have octahedral antimony coordination. These TSb6 octahedra share faces resulting in linear infinite strings with V - V and Cr - Cr bond distances of 301.5 and 304.0 pm, respectively. The structure of these com pounds contains building elements, which are also found in antimonides with ThCr2Si2, CaBe2Ge2, and HfCuSi2 type structures.

Abstract

The title compound was obtained by arc melting of the elemental components and subsequent annealing in a high frequency furnace. It crystallizes with the orthorhombic space group Cmmm, a = 779.26(7) pm, b = 1362.0(1) pm, c = 320.62(3) pm, V = 0.3403 nm3, Z = 2. The structure was determined from single-crystal X-ray data and refined to a residual of R = 0.021 (692 F values and 21 variables). It is closely related to the NaCl-structure. Three of the seven carbon atoms per formula unit form linear C3 -units with C-C bond lengths of 134 pm. They are coordinated to ten Sc atoms forming bicapped quadratic prisms. Additional isolated C atoms are located in octahedral voids formed by four Sc and two Re atoms. Together with the Re atoms they form two-dimensionally infinite [Re2C4 11-]n polyanions. The Re atoms have highly distorted tetrahedral carbon coordination with Re -C bond lengths of 200 and 208 pm corresponding to bond orders of about two. This coordination seems to be compatible with the 18-electron rule. The near-neighbour coordination of the Re atoms is assymmetric. It is suggested that this is due to the space requirements of nonbonding electrons. Samples of Sc5Re2C7 are semiconducting and weakly paramagnetic.

The title compounds have been prepared from the elemental components by arc-melting and subsequent annealing. Single crystals of U3TiSb5 and U3MnSb5 were obtained from a tin flux and their structures were determined from single-crystal X-ray data: P63/mcm, Z = 2; a = 913.9(2), c = 611.2(1) pm, R = 0.011 (233 structure factors, 14 variables) for U3TiSb5 and a = 916.8(2), c = 613.2(1) pm, R = 0.015 (427 structure factors, 14 variables) for U3MnSb5. The lattice constants of the isotypic compounds are: a = 908.2(2), c = 608.3(2) pm for U3VSb5 and a = 911.0(1), c = 611.5(1) pm for U3CrSb5. The structure of these antimonides may be regarded as an “anti”-type structure of Hf5Sn3Cu with the antimony atoms on the hafnium sites, while the positions of the uranium and transition metal atoms correspond to the positions of the tin and copper atoms. A comparison of the interatomic distances of U3TiSb5 with those of U3Sb4, USb2, and a-antimony suggests oxidation numbers according to (U+III)3Ti+IV(Sb1-III)3(Sb2-II)2, where the Sb2 atoms form weakly bonded chains

Abstract

Crystal Structure, Equiatomic Ternary Rare Earth Metal Cobalt Carbides The crystal structure of the new compound YCoC was determined from X-ray powder data. It is tetragonal, space group P42/mmc, with a = 0.36500(4) nm, c = 0.68636(9) nm and Z = 2 formula units per cell. The residual for a refinement of Debye-Scherrer data is R = 0.048 for 22 structure factors and 3 variable parameters. The structure is of a new type with no variable positional parameter. The arrangement of the metal atoms corresponds to that of the CsCl structure. The tetragonal superstructure with a doubled c axis arises through the ordered insertion of carbon atoms on octahedral sites formed by four Y and two Co atoms. The hydrolysis of YCoC in hydrochloric acid yields mainly methane, propane, and ethane. The compounds LnCoC (Ln = Gd -Tm, Lu) are isotypic with YCoC.

The new compounds Th5Fe19P12 and ThFe4P2 were prepared by reaction of the elemental components in a tin flux and their crystal structures were determined from single-crystal X-ray data. Th5Fe19P12 crystallizes with a new monoclinic structure type: C2/m, a = 2920.3(3), b = 379.18(3), c = 931.48(8) pm, β = 103.36(1)°, Z = 2, R = 0.031. ThFe4P2 is isotypic with SmNi4P2: P nnm, a = 1448.9(2), b = 1074.7(2), c = 376.98(4) pm, Z = 6, R = 0.030. Both compounds belong to the large family of structures with a metal : nonmetal ratio of exactly or nearly 2:1. In these phosphides all phosphorus atoms have nine metal neighbors: six are forming a trigonal prism with three additional neighbors capping the rectangular faces of the prism. In both structures the thorium atoms have trigonal prismatic or octahedral phosphorus coordination. Most iron atoms have the usual tetrahedral phosphorus environment. In addition, the structure of Th5Fe19P12 has iron atoms in rectangular and distorted square pyramidal phosphorus coordination, while the structure of ThFe4P2 contains iron atoms with only two or three phosphorus neighbors.