Metal-Metal Interactions in Dinuclear (triphos)Cobalt Complexes Exhibiting Mixed Valency

A theoretical study of the structure and stability of the dicarbonate ion has been performed at the Hartree-Fock, MP2, and QCI/SD levels. A flexible 6-31+G(d) basis set was used to allow for the diffuse electron density appearing in the anions. A stable anion corresponding to two CO2 entities covalently bound to a central oxygen has been found. The formation reaction starting from the carbonate anion and carbon dioxide has also been studied. Its thermodynamic features favour the formation of the dicarbonate anion, which in turn may account for the impressive solubility of carbon dioxide in carbonate melts.