A THEORETICAL-STUDY OF TE6(4+) AND TE4S4(2+)

Geometry optimizations and molecular orbital calculations were performed on Te6(4+) and Te4S42+ ions based on approximate density functional theory within the local-density approximation. The Te6(4+) ion was found to have an elongated trigonal-prismatic geometry (D3h) as its ground-state structure, in agreement with experimental results. A molecular orbital analysis of this non-classical structure in comparison to an alternative C2v boat structure for the Te6(4+) 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 C2v structure similar to that of the isoelectronic Se8(2+) ion.