Ab Initio Study of the Structures, Energetics, and Spectra of Aquazinc(II)

By using extensive ab initio calculations including electron correlation, we have studied the structures, thermodynamic quantities, and spectra of hydrated zinc ions [Zn(H2O)n2+ (n = 1−6)]. Various conformers for n = n1 + n2 (where n1 and n2 are the numbers of water molecules in the first and second hydration shells, respectively) were investigated along with their thermodynamic quantities. The entropy effect was found to be important for the stabilities. At 0 K, the most stable structures for n = 5 and 6 are 5 + 0 and 6 + 0, respectively. However, at room temperature, both 4 + 1 and 5 + 0 seem to be almost equally populated in the case of n = 5, while 6 + 0 is the most populated in the case of n = 6. The predicted successive binding energies for the addition of each water molecule to the zinc ion are reported. The vibrational frequency shifts, depending on the number of water molecules, were investigated along with the frequency characteristics, depending on the presence/absence of outer-shell water molecules.