Solvation of ligandopentaamminecobalt (III) complexes in dimethyl sulfoxide–water mixtures

Abstract

AbstractThe rate constants for the replacement of water from the inner‐coordination shell of Co(NH3)5OH23+, I, by dimethyl sulfoxide (DMSO) as DMSO gradually replaced water in the solvation shell of I were found to approach, and finally equal, the water‐exchange rate constant of I in aqueous media in accordance with expectation for a dissociative mechanism. Also the rate constants for the replacement of DMSO from the innercoordination shell of Co(NH3)5DMSO3+, II, by water as water replaced DMSO in the solvation shell of II were found to approach, and approximately equal, the DMSO‐exchange rate constant for II in liquid DMSO in accordance with expectation for a dissociative mechanism.The DMSO‐exchange rate constant for II in liquid DMSO was determined and found to be equal to (3.6 ± 0.8) × 10−4 sec−1 at 45°C.The dissociation quotient, [II] [NO3−]/[Co(NH3)5NO32+], was found to be equal to 0.28 ± 0.11 M at 45°C by NMR methods. The pseudo first‐order rate constants for anation of II by NO3− and the solvation of Co(NH3)5NO3 2+ by DMSO were determined at various temperatures.