Correlation between hydration and deprotonation in hexaaqua metal complexes

The hydration energy of metallic cations determined with density functional calculations using a double-numerical plus p-polarization basis set, related to the acidity constants of hexaaqua metal complexes, was investigated in the present study. From the results calculated by Vosko-Wilk-Nusair (VWN), Becke-Perdew (BP) and Becke-Lee-Yang-Parr (BLYP) density functionals, a global linear correlation with the observed acidity constants in both main group [Mg(II), Ca(II) and Al(III)] and (post-)transition group [Mn(II), Zn(II), Cd(II), Sc(III), Cr(III), Fe(III), Ga(III) and In(III)] hexaaqua metal complexes has been established:

VWN density functional: pK_a = 16.5760 + 0.0173E_hydr kcal mol⁻¹

BP density functional: pK_a = 15.7329 + 0.0182E_hydr kcal mol⁻¹

BLYP density functional: pK_a = 15.9448 + 0.0185E_hydr kcal mol⁻¹