RISM-SCF-SEDD Study on the Symmetry Breaking of Carbonate and Nitrate Anions in Aqueous Solution

The planarity of carbonate and nitrate anions was investigated in the gas and solution phases by means of the reference interaction site model self-consistent field spatial electron density distribution (RISM-SCF-SEDD) method. The computed optimized geometries and solvation structures are compared with the diffraction data. In the solution phase, the symmetry of carbonate anion is changed from D-3h, to C-3v, whereas the planarity of nitrate anion is still retained. These are fully consistent with experimental knowledge. The classical electrostatic model was also utilized to elucidate the mechanism of the symmetry breaking. It should be emphasized that the symmetry breaking occurs not only by a specific solvent molecule attaching to the ion but by an overall electrostatic interaction between the infinite number of solvent molecules and the ion.