Structure and dynamics of solvated Sn(II) in aqueous solution: an ab initio QM/MM MD approach

Structural and dynamical properties of the hydrated Sn(II) ion have been investigated by ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulations at double-zeta HF quantum mechanical level. The results indicate Sn(II)aq to be a rather peculiar, if not unique, case of a hydrated ion: four of its eight first-shell ligands do not take place in the otherwise frequent ligand-exchange processes, forming an approximately tetrahedral cage around the ion. The remaining ligands, however, exchange at a rate that is rather comparable to monovalent than divalent ions. This very surprising behavior of ligand exchange not yet observed in any previous simulation of over 30 hydrated metal ions is consistently confirmed by vibrational spectra, bond lengths, and a detailed analysis of the trajectories of the simulation.