Density functional study of the interaction of atomic silver with SiX (X = O, S) molecules

The spectroscopic properties of Ag ... SiX (X = O, S) have been studied at the B3LYP/6-311 + G(2d) level of theory. It has been shown that the metal atom is Si-bonded in a bent structure, with Ag-Si-X bond angles close to 110 degrees. The bond energy has been found to be -7.8 and -11.1 kcal mol(-1) for Ag ... SiO and Ag ... SiS, respectively. The experimental frequency shift of the SiX stretching mode owing to interaction with a silver atom and shifts resulting from isotope effects are very well described with DFT calculations. The Si-X bond lengths are longer in the complexes than in free SIX molecules. The Si-X force constants are decreased by ca. 9% and 12% from the isolated SiO and SiS to the Ag ... SiO and Ag ... SiS complexes, respectively. The charge transfer from metal to ligand has been calculated using the NBO partitioning scheme. It has been shown that the metal-ligand bond should be characterized by a low charge transfer (19% and 27% for Ag SiO and Ag SIS, respectively). The topological analysis of the electron density distribution shows that for both complexes the Ag-Si bond has a small electronic density at the critical point and should be characterized by electrostatic interaction and very little covalent contribution. It has been shown that the Ag ... SiS complex has a more covalent Ag-Si bond than the Ag ... SiO compound. Finally, the calculated Ag 5s spin density agrees well with the EPR experimental data, for both complexes.