Hydration of zinc ions: theoretical study of [Zn(H2O)(4)](H2O)(8)(2+) and [Zn(H2O)(6)](H2O)(6)(2+)

Herein, a quantum-mechanical (QM) investigation of the title complexes is r eported. Several different levels of QM theory (HF/6-31G*, B3LYP/6-31G*, MP 2/6-31G*, etc.) were employed in order to gain insights into the origin of the preference for six-coordination of hydrated Zn2+ ions which has been ob served experimentally. B3LYP/6-311 + G(2d,2p)//B3LYP/6-31G* calculations pr edict that the four coordinated structure [Zn(H2O)(4)](H2O)(8)(2+) is the m ost favorable one by 8 kJ/mol. At MP2/6-311 + G(2d,2p)//MP2/6-31G*, the [Zn (H2O)(6)](H2O)(6)(2+) complex is 28 kJ/mol more stable than the four-coordi nated configuration [Zn(H2O)(4)](H2O)(8)(2+), thereby, satisfactorily repro ducing the experimental observed preference for six-coordination. According to our analyses, the BF and B3LYP methods overestimate the contribution of hard and soft interactions to the Zn-water interactions, respectively, whe reas the MP? method gives a more balanced description. (C) 2000 Published b y Elsevier Science B.V.