%0 Journal Article %A Jackson, Virgil E. %A Felmy, Andrew R. %A Dixon, David A. %D 2015 %T Prediction of the pKa’s of Aqueous Metal Ion +2 Complexes %U https://acs.figshare.com/articles/journal_contribution/Prediction_of_the_p_i_K_i_sub_a_sub_s_of_Aqueous_Metal_Ion_2_Complexes/2182432 %R 10.1021/jp5118272.s001 %2 https://ndownloader.figshare.com/files/3816355 %K MP 2 level %K M øller perturbation theory %K solvation shell %K CPCM %K 2O %K solvation shell sizes %K prediction %K 1 pKa unit %K COSMO %K CCSD %K CN %K SCRF %K calculation %K cluster %K coordination number %K complex %K model %X Aqueous metal ions play an important role in many areas of chemistry. The acidities of [Be­(H2O)4]2+, [M­(H2O)6]2+, M = Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Hg2+, and [M­(H2O)n]2+, M = Ca2+ and Sr2+, n = 7 and 8, complexes have been predicted using density functional theory, second-order Møller–Plesset perturbation theory (MP2), and coupled cluster CCSD­(T) theory in the gas phase. pKa’s in aqueous solution were predicted by using self-consistent reaction field (SCRF) calculations with different solvation models. The most common binding motif of the majority of the metal +2 complexes is coordination number (CN) 6, with each hexaaquo cluster having reasonably high symmetry for the best arrangement of the water molecules in the first solvation shell. Be2+ is tetracoordinated, but a second solvation shell of 8 waters is needed to predict the pKa. The Ca2+ and Sr2+ aquo clusters have a coordination number of 7 or 8 as found in terms of the energy of the reaction M­(H2O)72+ + H2O → M­(H2O)82+ and the pKa values. The calculated geometries are in reasonable agreement with experiment. The SCRF calculations with the conductor-like screening model (COSMO), and the conductor polarized continuum model (CPCM) using COSMO-RS radii, consistently agree best with experiment at the MP2/aug-cc-pVDZ and CCSD­(T)/aug-cc-pVDZ levels of theory. The CCSD­(T) level provides the most accurate pKa’s, and the MP2 level also provides reliable predictions. Our predictions were used to elucidate the properties of metal +2 ion complexes. The pKa predictions provide confirmation of the size of the first solvation shell sizes. The calculations show that it is still difficult to predict pKa’s using this cluster/implicit solvent approach to better than 1 pKa unit. %I ACS Publications