Zn(H2O)2+6 is very stable among aqua-Zn(II) ions

Ab initio HF-SCF and MP2 calculations have been performed on Zn(H2O)2+n, where 4⩽n⩽8. The calculation with the Zn(8s4p2d)/O(4s2p1d)/H(2s) basis set shows that the fifth water molecule hydrating Zn(II) tends to have one more water molecule in the first hydration shell, while the seventh water molecule tends to be in the second hydration shell. Thus, we have provided evidence from ab initio calculations that hexaaqua-Zn(II) is very stable among aqua-Zn(II) ions, unless unusual thermodynamic conditions apply. The structure of the hexaaqua-Zn(II) has Th symmetry. The solvation energy contribution due to the primary hydration accounts for more than 50% of the experimental solvation energy of Zn(II). We also discuss the structure, hydration energy and spectra, comparing with experimental data.