Evaluation of tin-oxygen bond association by means of ab initio molecular orbital calculations

Ab initio calculations with MP2 provide reliable information about structure and bonding of organotin molecules. The association behavior of organotin alkoxides is counterbalanced by conflicting enthalpy and entropy contributions. The increase in Lewis acidity of tin induced by attachment of alkoxy group(s) is of prime importance for the association. On the other hand, formation of the stable dimeric distannoxanes has been proved by great negative Delta G values. The oxygen atom between the tin atoms in distannoxanes has stronger Lewis basicity than that in organotin alkoxides. The multiplier effect of both Lewis acidity of tin and Lewis basicity of oxygen is reflected on the shortening of the secondary Sn-O bond. As a whole, tin-oxygen bonds have been successfully elucidated for the first time by ab initio calculations.