Different Carbonate Isomers Formed by the Addition of CO to MO for M = Ti, Zr, and Hf.

The chemisorption addition of CO to MO and MO for M = Ti, Zr, and Hf was examined using couple cluster CCSD(T) theory using density functional theory B3LYP geometries. For neutral MOCO, a bridge chemisorbed tridentate carbonate cluster is the lowest energy for Ti and Zr, and a terminal chemisorbed bidentate carbonate is the lowest energy for Hf. For anionic MOCO, the lowest energy structure is a terminal chemisorbed bidentate carbonate for all three metals. The use of correlation-consistent weighted core basis sets for the CCSD(T) calculations is shown to be necessary to obtain the correct energy ordering for the isomers. Only for TiOCO is a center tridentate carbonate cluster a low energy isomer. The electron affinities of MOCO are ∼0.2 eV larger than for MO. The CO chemisorption binding energies increase slightly for MO as compared to those for MO.