Distorted five-fold coordination of Cu2+(aq) from a Car–Parrinello molecular dynamics simulation

Abstract

The solvation shell structure and dynamics of a single Cu²⁺ ion in a periodic box with 32 water molecules under ambient conditions has been investigated using Car–Parrinello molecular dynamics simulations in a time-window of 18 ps. Five-fold coordination with four equidistant equatorial water molecules at 2.00 Å and one axial water molecule at 2.45 Å from the Cu²⁺ ion is found. A “hole” without water molecules is found on the opposite side of the axial water. The ion–water bonding character for the equatorial water molecules is different from that of the axial water molecules, as shown by a localized orbital analysis of the electronic structure. Moreover, the calculated OD stretching vibrational band for the equatorial water molecules lies ca. 175 cm⁻¹ below the axial-water band, in good agreement with experimental data. The equatorial-water band lies below, and the axial-water band above, the pure liquid D₂O band, also in agreement with experimental data.