Can Quantum Chemical Methods be Used to Predict Gibbs Energies for Reactions in Solution? A Case Study Using Binary and Ternary Lanthanide(III) and Actinide(III) - Tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione] (TTA) - Tributyl/Trimethyl phosphate (TBP/TMP) Complexes.
Résumé
Quantum chemical (QM) methods have been used to calculate the changes in free energy, ΔG o, for adduct formations such as Ln(TTA)3(OH2)2(org) + TMP(org) Ln(TTA)3(TMP)(OH2)(org) + H2O (1) in CHCl3 and two phase equilibria such as Ln3+(aq) + 3HTTA(org) Ln(TTA)3(org) + 3H+(aq) (2). In these reactions TTA and TMP represent the chelating acidic extractants thenoyltrifluoroacetone and the trimethyl phosphate synergist. The use of theory requires approximations of both of the theoretical methods and the chemical models used. Different models have been compared and tested against experimental data, demonstrating that theoretical methods provide accurate information on structures and on some features of chemical bonding, while thermodynamic data have much larger uncertainty. However, by suitable choice of chemical models the latter can be decreased significantly, allowing reasonably good estimates of trends in reaction energies throughout the Ln(III) and An(III) series.