On the Electronic Coupling of the CO Stretching Vibrations in Cl2Pt(malonate)

Ab initio calculations on the complex Cl2Pt(malonate)- have been performed to estimate the magnitude and the source of the splitting between the symmetric and antisymmetric CO stretches. It is shown that a large part of the splitting can result from pure electronic coupling mediated via the π-structure of the ligand. Calculations have also been performed on the free ligand malonate- and the neutral malonaldehyde that show decreasing electronic coupling, which is consistent with the decreasing resonance stabilization. A simple effective CO interaction potential has been produced for Cl2Pt(malonate)- that is used to estimate the electronic splitting of the 1600 cm-1 IR band to 137 cm-1. Anharmonic contributions seem to reduce this value somewhat, but the magnitude and sign of the splitting is similar to the experimental value of 183 cm-1 found for the similar Cl2Pt(acac)- complex.