Effect of solvent on reactions of coordination complexes-Thorium (IV)-catalysed aquation of oxalatopentaamminecobalt (III) in aqueous-alcohol media†

Abstract

The kinetics of title reaction have been investigated in aqueous alcohol media using methanol, propan-2-ol, t-butanoi and ethylenegiycol. The efficiency of Th⁴⁺ in promoting water for C₂O₄OTh²⁺ substitution at Co(III) centre of the binuclear species (NH₃)₅CoC₂OTh⁵⁺ is 20 times larger (<em>k</em>_M<em>/k</em>_H 20 at 50°C and fully aqueous medium) than that for H⁺ indicating importance of the charges and Lewis basicities of the leaving groups. With increasing proportion of any of the cosolvents (vol % of alcohols 10, 20 and 50) the rate constant for the binuclear complex (<em>k</em>_M) decreases only to a small extent and the title reaction in D₂O-H₂O medium is only slightly slower than in fully aqueous media (<em>k</em>_M(D₂O)/<em>k</em>_M(D₂O) <em>= </em>1.12 for 50% (v/v)D₂O/H₂O at 65°C.