Unusual Disordering of Potassium Ions in the Structures of Cluster Rhenium Thiohalides K3[Re6S7Br7] and K4[Re6S8Cl6

Abstract

New cluster compounds — rhenium and potassium thiohalides K3Re6S7Br7 (I) and K4Re6S8Cl6 (II) — have been synthesized. Their crystal structures have been determined by single crystal X-ray diffraction. The compounds are monoclinic; (I): space group P21/c, a = 9.32(1) A, b = 13.528 A, c = 12.413 A, β = 110.21°, Z = 2, R = 0.038; (II): space group C2/m, a = 10.614 A, b = 17.268 A, c = 10.448 A, β = 110.755°, Z = 2, R = 0.042. In both structures, the potassium ions are considerably distorted. The occupancies of the potassium sites are 0.17-0.34 (I) and 0. 01-0.26 (II), correlating well with the coordination numbers (c.n. 7-10 and 2-7 for I and II, respectively). In I, adjacent positions of potassium atoms are aggregated into discrete tetrahedral and angular clusters; in II, the individual (four-and six-membered) cyclic clusters of potassium sites are present along with bent chains of vertex-and edge-sharing tetrahedral “potassium clusters.” The shortest K-K distances in these “clusters” vary from 1.31 A to 1.54 A (I) and from 0.66 A to 1.65 A (II). The “instability” of the potassium site suggests that I and II are ion conductors.