Outer‐Sphere Hydration and Liquid−Liquid Partition of Metal(III) Chelates − Density Functional Calculations

Abstract

AbstractHydration of two coordinatively saturated metal chelates, tris(propane‐1,3‐dionato)scandium(III) and tris(propane‐1,3‐dionato)cobalt(III), was studied theoretically using the density functional method with a three‐parameter B3LYP implementation at different variants for calculating the hydration energy, including corrections for ZPVE, BSSE, polarisation functions, temperature and the number of hydrating water molecules in the system. Formation of hydrates was demonstrated, with water hydrogen‐bonded to ligands (outer‐sphere hydration). After corrections for side effects, good correlations were found between the energy and the length of these hydrogen bonds in the hydrates of both chelates. Also, the calculated changes in charge distribution on the atoms of hydrogen‐bonded water in these model chelates qualitatively agree with the experimental 1H NMR spectroscopic data for the analogous tris(pentane‐2,4‐dionato)cobalt(III) species. An implicit solvation model (SCI‐PCM) was used to take into account solvent effects of water and heptane on the energies of the model chelates studied and to calculate their enthalpies of transfer from heptane to water. In spite of simplifications in the model, satisfactory agreement was found between the calculated values and the experimental standard enthalpies of transfer of the analogous chelates, namely the tris(pentane‐2,4‐dionates) of scandium and cobalt(III). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)