Ab Initio and DFT Study of Magnesium Sulfate Contact Ion Pairs

The stuctures of contact ion pairs of magnesium sulfate were studied. The geometries of contact ion pairs of MgSO4(H2O)n (n=1-6) were optimized by using Hartree-Fock (HF/6-31+G*, HF/6-311+G**) and density functional theory (DFT) (B3LYP/6-31+G*, B3LYP/6-311+G**) methods. The stable structures of monodentate, bidentate and tridentate contact ion pairs were obtained. The bidentate structure of contact ion pairs are the most stable compaired with the monodentate and tridentate ones for the same composition. The hydration enthalpies of contact ion pairs of MgSO4 (H2O)n (n=1-4) increase with their hydration numbers.