Computational study of lanthanide(iii) hydration

Abstract

Lanthanide(III) hydration was studied by utilizing density-functional theory and second-order Møller–Plesset perturbation theory combined with scalar-relativistic 4f-in-core pseudopotentials and valence-only basis sets for the Ln^III ions. For [Ln^III(H₂O)_h]³⁺ (h = 7, 8, 9) and [Ln^III(H₂O)_h−1·H₂O]³⁺ (h = 8, 9) molecular structures, binding energies, entropies and energies of hydration as well as Gibbs free energies of hydration were calculated using (8s7p6d3f2g)/[6s5p5d3f2g] basis sets for Ln^III and aug-cc-pV(D,T)Z basis sets for O and H in combination with the COSMO solvation model. At the generalized gradient approximation level of density-functional theory a preferred hydration number of 8 is found for La^III–Tm^III and 7 for Yb^III–Lu^III, whereas hybrid density-functional theory predicts a hydration number 8 for all Ln^III. At the SCS-MP2 level of theory the preferred hydration number is found to be 9 for La^III–Sm^III and 8 for Eu^III–Lu^III in good agreement with experimental evidence.