Petra Stoll scite author profile

A different class of layered systems derived from ThCr 2 Si 2 -type materials is introduced and studied. We present preparation, x-ray analysis, band-structure, and total-energy calculations of KCu 2 Se 2 , a semimetallic representative of this class. The crystal has an orthorhombic symmetry by a slight distortion of a tetragonal lattice. From calculation, interesting quasi-two-dimensional electronic properties are obtained similar to those of the well-known hexagonal transition-metal dichalcogenides. A complex picture of chemical bonding in this mixed-valency compound is elucidated by electronic structure calculations. The changes in the band structure caused by the symmetry reduction and their implications for the total energy are discussed. The ab initio band-structure calculation is performed with the extended linear augmented plane-wave k•p method, with all the states down to K 3s being treated as valence states. The total energy is computed using the augmented Fourier component representation of the crystal potential.

Synthesis and Crystal Structure of KCuGd2S4: A Threedimensional Framework with Isolated Channels

Dürichen

et al. 1998

Z. anorg. allg. Chem.

The reaction of K2S5, Cu, Gd, and S in a 2 : 1 : 2 : 4 molar ratio at 450 °C yields yellow‐orange needle‐like cuboids of the new quaternary compound KCuGd2S4. The crystal structure represents a novel three‐dimensional structure type of quaternary rare earth chalcogenides with alkali metal. The compound crystallizes in the orthorhombic space group Cmcm (No. 63) with a = 3.9921(1) Å, b = 13.523(3) Å, c = 13.802(3) Å, V = 745.1(3) Å3, Z = 4. In the structure GdS6 octahedra and CuS4 tetrahedra are joined by common edges and corners forming corrugated layers parallel to (010). The GdS6 octahedra are connected via common edges in the third dimension thus leading to the formation of a three‐dimensional tunnel structure. The potassium cations are confined within the pentagonal shaped channels and are surrounded by eight sulfide anions each.

Synthesis, crystal structure and optical properties of the new tantalum polysulfide Rb6Ta4S25 and its thermal degradation to Rb6Ta4S22

Jeß

et al. 2000

Solid State Sciences

Syntheses and Crystal Structures of a New Niobium Polysulfide K6Nb4S22 and two New Dimorphic Tantalum Polysulfides K6Ta4S22

Bensch

2002

Z. anorg. allg. Chem.

The new compounds K 6 Nb 4 S 22 and K 6 Ta 4 S 22 (I) have been synthesised by the reaction of NbS 2 or Ta metal in a K 2 S 3 flux. Using TaS 2 as educt a second modification of K 6 Ta 4 S 22 (II) is obtained. K 6 Nb 4 S 22 and K 6 Ta 4 S 22 (form I) crystallise in the monoclinic space group C2/c with a ϭ 35.634 (2) Å , b ϭ 7.8448 (4) Å , c ϭ 12.1505 (5) Å , β ϭ 100.853 (5)°, V ϭ 3335.8 (3) Å 3 , and Z ϭ 4 for K 6 Nb 4 S 22 and a ϭ 35.563 (7) Å , b ϭ 7.836 (2) Å , c ϭ 12.139 (2) Å , β ϭ 100.56 (3)°, V ϭ 3325.5 (2) Å 3 , and Z ϭ 4 for K 6 Ta 4 S 22 (I). The second modification K 6 Ta 4 S 22 (form II) crystallises in the monoclinic space group P2 1 /c with a ϭ 7.5835 (6) Å , b ϭ 8.7115 (5) Å , c ϭ 24.421 (2) Å , β ϭ 98.733 (9)°, V ϭ 1594.6 (2) Å 3 , and Z ϭ 2. The structures consist of [M 4 S 22 ] 6Ϫ anions composed of two M 2 S 11 sub-units which are linked into M 4 S 22 units via terminal sulfur ligands. The anions are well separated by the

Synthesis and Crystal Structure of Rb ₆ Ta ₄ S ₂₂ : The First Tantalum Polysulfide Composed of the Dimeric Complex Anion [Ta ₄ S ₂₂ ] ^6–

Jeß

et al. 2000

Z. anorg. allg. Chem.

The reaction of Rb2S3, Ta and S in a 1.3 : 1 : 5.6 molar ratio at 400 °C yields red‐orange crystals of the new ternary compound Rb6Ta4S22 being the first tantalum polysulfide containing the dimeric complex anion [Ta4S22]6–. The polysulfide anions are composed of two Ta2S11 subunits which are linked to Ta4S22 units via terminal sulfur ligands. The Ta5+ centers are coordinated by S22– and S2– ligands according to [(Ta2(μ2‐η2,η1‐S2)3(η2‐S2)(S)2)2(μ2‐η1,η1‐S2)]6–. Every Ta5+ ion is surrounded by seven sulfur ions forming a strongly distorted pentagonal bipyramid. In the crystal structure the discrete [Ta4S22]6– anions are stacked parallel to the crystallographic b‐axis. The Rb+ cations are located between these stacks. Rb6Ta4S22 crystallizes in the monoclinic space group P21/c (No. 14) with a = 11.8253(9) Å, b = 7.9665(4) Å, c = 19.174(2) Å, β = 104.215(9)°, V = 1751.0(2) Å3, Z = 2.