Theoretical study of the different coordination modes of copper-carbon dioxide complex

The copper-carbon dioxide bonding is investigated through ab initio effective potential calculations including electron correlation effects. The geometries and relative stabilities are calculated for the four possible modes of coordination of CO/sub 2/ to a single copper atom. Apart from the side-on-bonded Cu(CO/sub 2/) which may be formulated as a weakly bound van der Waals-type complex, only the end-on Cu-O-C=O complex (/sup 2/A') is found to be stable with respect to Cu + CO/sub 2/ fragments by 6 kcal mol/sup -1/. The end-on coordination mode is predicted to have C/sub s/ symmetry and a bent geometry (cis form). It is characterized by an important charge transfer from copper to CO/sub 2/ with the unpaied electron located at the carbon atom. Both cyclic O-coordinated and C-coordinated complexes are found to be unstable by about 8 and 46 kcal mol/sup -1/, respectively. Only the end-on complex seems to be consistent with the infrared and Raman spectra observed in a CO/sub 2/ matrix at low temperatures.