Structures and Solvation Energies Effects Versus Temperature. An MP2 Investigations in the Framework of Cluster Model

Structures, relative stabilities, solvation enthalpies, and free energies of the ${\left(\mathrm{Be}{\left(H_{2}O\right)}_{n=12}\right)}^{2+}$ cluster in gas and in water phases were investigated in this work using Moller-Plesset perturbation theory (MP2) and considering a temperature range of 40–400 K. The 12 H₂O molecules are distributed between the first, second, and third solvation shells. The calculated distances ${\mathrm{Be}}^{2+}-O$ distances in gas phase are in good agreement with the experimental range which confirms the strong influence of long-distance interactions in cluster stabilization. Structural comparison between gas and water phases shows that the addition of the bulk solvent causes changes in the cation-water bond lengths of few hundredths of angstroms. The obtained solvation free energy of beryllium ion in water at room temperature (298.15 K) results in b − 575.1 kcal mol⁻¹ in very good agreement with the corresponding experimental counterpart. The computed solvation free energies increase as a polynomial function of the temperature while the change in the solvation enthalpies is found to be negligible.