W0005

Platinum Silicon Antimonide, PtSiSb. Meitian Wang, Mark G. Morgan, and Arthur Mar, Dept. of Chemistry, Univ. of Alberta, Edmonton, AB Canada T6G 2G2.

The equiatomic compound PtSiSb is the first phase found in the Pt-Si-Sb system. It is closely related to PtSiTe (Mansuetto, M. F.; Ibers, J. A. Z. Kristallogr. 1994, 209, 708), adopting a ternary ordered pararammelsbergite (a-NiAs₂) type structure, an intermediate between the pyrite and marcasite structures. PtSi₃Sb₃ octahedra are condensed through both corner- and edge-sharing. The electron count in PtSiSb is 19 e^- per formula unit, one electron less than that for all previously known a-NiAs₂-type structures. This oxidation results in a significant distortion in PtSiSb arising from the formation of metal-metal bonded pairs, not present in other a-NiAs₂-type structures. Extended Huckel calculations reveal that the depopulation of Pt-Pt antibonding levels is responsible for the distortion on going from PtSiTe (20 e^-) to PtSiSb (19 e^-).