Reaction between [Os-VI(tpm)(Cl)(2)(N)](PF6) (tpm = tris(1-pyrazolyl)methane) (1) or Os-VI(Tp)(Cl)(2)(N) (Tp = hydrotris(1-pyrazolyl)borate anion) (2) and CS2 + N-3(-) in acetone gives the corresponding thionitrosyl complexes, -SCN, and N-2. There is an extensive reactivity chemistry of the thionitrosyl group in [Os-II(tpm)(Cl)(2)(NS)](PF6) (3b). Reaction between 3b and PPh3 occurs with S-atom transfer to give [Os-IV(tpm)(Cl)(2)(NPPh3)](+) and S=PPh3. 3b undergoes chemical or electrochemical reduction to give the corresponding Os-II ammine complex and H2S. O-atom transfer from O=NMe3 to 3b occurs to give Os-III(tpm)(Cl)(2)(NSO). Competitive NO+/NS+ exchange and S2- transfer occur in the reaction between [Os-II(tpm)(Cl)(2)(NS)] (BF4) (3c) and NO+ to give a mixture of [Os-VI- (tpm)(Cl)(2)(N)](+) and [Os-II(tpm)(Cl)(2)(NO)](+).