A theoretical study of Te64+ and Te4S42+

Abstract

Geometry optimizations and molecular orbital calculations were performed on Te₆⁴⁺ and Te₄S₄²⁺ ions based on approximate density functional theory within the local-density approximation. The Te₆⁴⁺ ion was found to have an elongated trigonal-prismatic geometry (D_3h) as its ground-state structure, in agreement with experimental results. A molecular orbital analysis of this non-classical structure in comparison to an alternative C_2v boat structure for the Te₆⁴⁺ ion was performed and an explanation is offered for their relative stabilities. Experimentally, the Te₄S₄²⁺ ion is reported to adopt a geometry isostructural to As₄S₄. The present calculations on Te₄S₄²⁺ with the experimental geometry indicate that the ion has a half-filled doubly degenerate highest occupied molecular orbital which is strongly antibonding between the tellurium atoms. The geometries of Te₄S₄²⁺ with triplet and singlet electronic structures have been optimized. These geometries differed from the experimental geometry, with a considerable lengthening of the Te–Te bonds for the triplet species, and cleavage of a Te–Te bond for the singlet species to produce a C_2v structure similar to that of the isoelectronic Se₈²⁺ ion.