True space group of spinel-type chromium oxides and sulfides, and ternary lithium chlorides – band structure calculations

Abstract

The results of band structure (extended Hückel procedure) and cohesive energy calculations of spinel-type chromium oxides and sulfides, and of lithium vanadium chloride were presented. They confirm that the D3dto C3vsymmetry reduction of the octahedrally coordinated metal ions (Cr, V) of the respective oxides and of Li2VCl4(space group F-43m instead of Fd-3m) is caused by relatively strong metal-metal bonds with crystal orbital overlap populations (COOP) up to 10% of those of the metal-oxygen bonds despite M-M distances ≅300pm. In the case of spinel-type chromium sulfides, the Cr-Cr interactions are antibonding in nature and, hence, no symmetry reduction occurs.