Thermodynamics of binding of Li+, Na+, Mg2+ and Zn2+ to Lewis bases in the gas phase

B3LYP/6-311 + G(d,p) DFT method was used to characterize the 92 gas-phase complexes of 23 neutral and anionic ligands H2O, NH3, PH3, H2S, H2Si, HF, HCI, H2Ge, t-HSiOH, t-HGeOH, H2C=O, NH2(H)C=O, HCOOH, H2Ge=O, H2Si=O, H2C=NH, HCN, CO, OH-, SH-, SiH- and HCOO- with Li+, Na+, Mg2+ and Zn2+. The basicity order of the ligands studied towards those cations exhibits a different ordering. There is no general correlation of basicities towards cations investigated. However, a very good correlation was found between the basicities towards monovalent cations Li+ and Na+ and between the basicities towards divalent cations Mg2+ and Zn2+. Calculated values of interaction enthalpies and free energies vary as Zn2+ > Mg2+ much greater than Li+ > Na+. The relative basicities of the bases studied depend characteristically on type of cation and co-ordination base. (C) 2000 Elsevier Science B.V. All rights reserved.