Ab initio investigation on the ion-associated species and process in Mg(NO₃)₂ solution

In the present article, two focal subjects, i.e., hydration of the NO ^- and associated ion species in the Mg(NO₃)₂ solution are researched by using the ab initio method. Nitrate ions with the hydration number of 1-6 are optimized at the HF/6-31+G* level. Their relative energies, binding energies, and v₁-NO^- frequencies are also presented. The investigation of the binding energies shows the hydration number is 3-6 in the solvent abundant environment. The associated species, including ion pairings, triple- and multiple-ion clusters, are also optimized at the same level and their v₁-NO₃^- frequencies are calculated for comparing with the results in experiments. From the comparison, the new associated process via aqueous free ions → solvent-shared ion pairings → solvent-shared triple and multiple ion clusters → contact multiple ion clusters → amorphous crystal is proposed.