Reactions of the small tin clusters with carbon monoxide:: Infrared spectra and DFT calculations of the SnnCO (n=2-5) and Sn2(CO)2 molecules in solid argon

Laser-ablated Sn atoms have been co-deposited with CO molecules in solid argon to produce tin carbonyls. In addition to the previously reported Sn(CO)(n) (n = 1 and 2) molecules, small tin cluster carbonyls SnnCO (n = 2-5) and Sn-2(CO)(2) are formed on sample annealing, and are characterized using infrared spectroscopy on the basis of the results of the isotopic substitution, the CO concentration change, and the comparison with theoretical predictions. It is found that Sn2CO, Sn3CO, and Sn5CO are bridge-bonded carbonyl compounds, whereas Sn-2(CO)(2) and Sn4CO are terminal-bonded carbonyl molecules. The Sn-2(CO)(2) species observably undergoes photo-induced decomposition to Sn(CO)(2). Another interesting finding is that the absorption of Sn4CO shifts from 1994.0 to 1989.8 cm(-1) by UV light irradiation, probably due to the change of the electronic state or the matrix effect. The density functional theory calculations have been performed on these molecules and the corresponding small naked tin clusters. Furthermore, energetic analysis for the possible reactions of lead atoms with CO molecules is also given.