SYNTHESIS AND CRYSTAL-STRUCTURES OF K5SE3, CS5TE3 AND CS2TE

We describe the syntheses and the crystal structures of K5Se3, Cs5Te3, and Cs2Te. The substructure of low-temperature-(LT-)K5Se3 was solved by single crystal X-ray analysis (a = 18.289(3) angstrom, b = 5.861(2) angstrom, c = 12.988(2) angstrom, beta = 134.82(1)-degrees, Z = 4, C2/m); it is a monoclinic distortion of the K5Te3-type, which itself is closely related to the W5Si3-type. Furthermore, we propose a model for the incommensurate superstructure of LT-K5Se3, which reproduces the main features of the observed satellites. By X-ray powder diffraction we determined the structures of high-temperature-(HT)-K5Se3 (K5Te3-type: cell constants at 200-degrees-C: a = 13.097(1) angstrom, c = 5.882(1) angstrom, Z = 4, 14/m), Cs5Te3 (LT-K5Se3-type: a = 21.11(2) angstrom, b = 6.655(1) angstrom, c = 15.07(1) angstrom, beta = 134.53(5)-degrees, Z = 4, C2/m), and Cs2Te (PbCl2-type: a = 9.109(2) angstrom, b = 5.871(1) angstrom, c = 11.494(2) angstrom, Z = 4, Pnma), and, with additional thermoanalytic methods, we investigated the phase transition LT-K5Se3 reversible HT-K5Se3.