Reactivity of low-coordinated MgO anions towards CO: A DFT study of (CnOn+1)2− polymeric species

The reactivity of low-coordinated anions of MgO towards CO has been studied by means of ab initio cluster model DFT calculations. Differently from MgO terraces, where the O2− anions are totally unreactive, oxide anions at step, edge and corner sites exhibit a very high basicity and reactivity towards CO. The reaction: [OLC(CO)n−1]2− (s) + CO (g) → [OLC(CO)n]2− (s) leads to the formation of polymeric (CnOn+1)2− species, where n goes from 1 to 5. The reaction is non-activated and exothermic; only the formation of the tetramer appears to be nearly thermoneutral. The formation of the hexamer (n = 6) is thermodynamically unfavorable. For each value of n, several isomers have been considered. The vibrational properties of the [OLC(CO)n]2− surface complexes have been computed and used to interpret the low-temperature infrared spectra obtained in the group of Zecchina [G. Spoto, E.N. Gribov, G. Ricchiardi, A. Damin, D. Scarano, S. Bordiga, C. Lamberti, A. Zecchina, Prog. Surf. Sci. 76 (2004) 71].