CO2 coordination to nickel atoms: Matrix isolation and density functional studies

The interaction of the CO2 molecule with nickel atoms was studied by using matrix isolation spectroscopy and density functional theory. In argon dilute matrices, no reaction occurs, even after annealing the deposit. In neat CO2 matrices, it is shown that carbon dioxide forms a 1:1 complex with nickel which is characterized by its UV-visible and FTIR absorptions, including isotopically labeled species. Theory predicts the side-on coordination mode to be the most stable. The binding energy of the side-on Ni(CO2) complex is estimated to be 18 kcal/mol. The calculated OCO angle is 145 degrees, which is quite a large value compared to those encountered in other known CO2 complexes. In dinitrogen matrices, the yield of CO2 complexation is considerably enhanced relative to that in argon dilute and neat CO2 matrices, which is attributed to the formation of unsaturated Ni(N-2)(n) complexes prior to CO2 coordination. The CO2 binding energies calculated for the Ni(CO2)(N-2)(n) (n = 1, 2) complexes (respectively 32 and 4 kcal/mol) suggest that CO2 probably coordinates to the Ni(N-2) complex. This is a very interesting result, owing to the fact that CO2 does not react with nickel atoms in dilute argon matrices.