Theoretical, thermal, and coordination chemistry of the amphoteric thiazate (NSO–)1 ion

Abstract

The isomers of thiazate (NSO–) have a rich chemistry that is examined theoretically and experimentally for their thermal and coordination characteristics. The intramolecular isomerization of NSO– to monothionitrite (ONS–) is predicted (B3LYP/6-311+G*) to have a substantial barrier, greater than 418 kJ mol–1. Thus, thiazates are expected to be relatively thermally stable towards isomerization, and DSC indicates that KNSO undergoes a two stage irreversible thermolytic decomposition only beginning at 132 °C with ΔH = –116.3 kJ mol–1. As a ligand, the thiazate can adopt a range of geometries in response to the metal's oxidation state and ligand sphere. For example, in Ru(TTP)(NO)(NSO) the ligand has a markedly bent Ru-N-S geometry, and when contrasted with other structurally characterized thiazate coordination compounds, it is concluded that in addition to σ donation the thiazate binds to metals in an amphoteric manner because of either a forward or reverse OSN → M π donation similar to transition metal nitrosyl, amido, and imido complexes.Key words: thiazate, isomerization, thermolysis, amphoteric ligand, coordination chemistry.