title: Density functional theoretical study on the preferential selectivity of macrocyclic dicyclohexano-18-crown-6 for Sr⁺² ion over Th⁺⁴ ion during extraction from an aqueous phase to organic phases with different dielectric constants.
abstract: The preferential selectivity of dicyclohexano-18-crown-6 (DCH18C6) for bivalent Sr(+2) ion over tetravalent Th(+4) ion was investigated using generalized gradient approximated (GGA) BP86 and the hybrid B3LYP density functional, employing split valence plus polarization (SV(P)) and triple-zeta valence plus polarization (TZVP) basis sets in conjunction with the COSMO (conductor-like screening model) solvation approach. The calculated theoretical selectivity of DCH18C6 for Sr(+2) ion over Th(+4) ion was found to be in accord with the selectivity for Sr(+2) ion over Th(+4) ion observed when performing liquid-liquid extraction experiments in different organic solvents. While 1:1(M:L) stoichiometric complexation reactions can be used to predict the preferential selectivity of Sr(2+) ion over Th(4+) ion, the results obtained are not consistent with the experimental results observed upon increasing the dielectric constant of the solvent. The calculated theoretical gas-phase data for the free energy of complexation, ∆G, fail to explain the selectivity for Sr(+2) ion over Th(+4) ion. However, when 1:2 (M:L) stoichiometric complexation reactions (reported in previous X-ray crystallography studies) are considered, correct and consistent results for the selectivity for Sr(+2) ion over a wide range of dielectric constants are predicted. The distribution constant for Sr(2+) and Th(4+) ions was found to gradually increase with increasing dielectric constant of the organic solvent, and was found to be highest in nitrobenzene. The selectivity data calculated from ∆∆G ext are in excellent agreement with the results obtained from solvent extraction experiments.
authors.affiliation: Chemical Engineering Division, Chemical Engineering Group, Bhabha Atomic Research Centre, Mumbai, 400 085, India.
authors.forename: A
authors.initials: A
authors.lastname: Boda
authors.forename: J M
authors.initials: JM
authors.lastname: Joshi
authors.forename: Sk M
authors.initials: SM
authors.lastname: Ali
authors.forename: K T
authors.initials: KT
authors.lastname: Shenoy
authors.forename: S K
authors.initials: SK
authors.lastname: Ghosh