Characterization of structure and dynamics of an aqueous scandium(iii) ion by an extended ab initio QM/MM molecular dynamics simulation

Abstract

Hydration structure and dynamics of an aqueous Sc(III) solution were characterized by means of an extended ab initio quantum mechanical/molecular dynamical (QM/MM) molecular dynamics simulation at Hartree–Fock level. A monocapped trigonal prismatic structure composed of seven water molecules surrounding scandium(III) ion was proposed by the QM/MM simulation including the quantum mechanical effects for the first and second hydration shells. The mean Sc(III)–O bond length of 2.14 Å was identified for six prism water molecules with one capping water located at around 2.26 Å, reproducing well the X-ray diffraction data. The Sc(III)–O stretching frequency of 432 cm⁻¹ corresponding to a force constant of 130 N m⁻¹, evaluated from the enlarged QM/MM simulation, is in good agreement with the experimentally determined value of 430 cm⁻¹ (128 N m⁻¹). Various water exchange processes in the second hydration shell of the hydrated Sc(III) ion predict a mean ligand residence time of 7.3 ps.