Effect of pressure on the aquation reactions of a series of bidentate carbonato-complexes of CoIII in aqueous solution

TLDR: The absence of such a difference for the Co(en)2CO3+ species and the magnitude of the volumes of activation suggest a ring-opening mechanism of the Ia type, and no significant pressure effects were observed for the decarboxylation reactions.

Abstract: The pressure dependencies of spontaneous and acid-catalyzed ring-opening, and subsequent decarboxylation reactions were studied for the complexes Co(en)2CO3+, α- and β-Co-(edda)CO3− and Co(nta)CO32−. The volumes of activation for the spontaneous ring-opening process of the anionic carbonato complexes areca. 10 cm3 mol−1 more negative than those for the corresponding acid-catalyzed process, and are ascribed to the increase in electrostriction around the free end of the carbonate ligand produced during the dissociative ring-opening step. The absence of such a difference for the Co(en)2CO3+ species and the magnitude of the volumes of activation suggest a ring-opening mechanism of the Ia type. No significant pressure effects were observed for the decarboxylation reactions. A plausible explanation is offered.