New Ternary Rhenium Chalcogenides with Isolated (Re6X8)-Cluster Units: Preparation and Properties

摘要

New ternary rhenium chalcogenides A4Re6X12 with A =T1, Cu, Na, Cs, and X = Se; A = T1, Rb and X = S; A2Re6X12 with A = Pb and X = S, Se have been prepared by high temperature and ion exchange techniques in closed systems. X ray diffraction powder patterns show them to be isostructural with previously reported A4Re6X12 which are characterized by Re6X8 cluster units interconnected into a three-dimensional network structure by X and X2 linkages. Temperature variation of resistivity measured on sintered pellets shows semiconducting behavior in agreement with 24 electrons per cluster filling the bonding valence bond which is separated in energy from the empty antibonding conduction band. Variation of the number and size of the A and X ions are correlated with structural stability in these compounds. (mjm)