Molecular dynamics simulations on europium nitrate complexes with neutral organophosphorus ligands. What governs the stoichiometry and extractability of the complex?

Abstract

Molecular dynamics simulations have been performed in water on europium nitrate complexes Eu(NO 3 ) 3 L m with three neutral organophosphorus extractants (L = tri-n-butylphosphate (TBP), triphenylphosphine oxide (TPPO) and carbamoylphosphine oxide (CMPO)) in order to determine which factors govern the experimental 1 : 3 stoichiometry in organic solution saturated with water. This stoichiometry was investigated by progressive saturation of the cation coordination sphere by L. Simulations without constraints lead to monodentate coordination of the NO 3 Ϫ anions to Eu 3ϩ , and to stoichiometries higher than 1 : 3. When the NO 3 Ϫ ions are constrained to bind Eu 3ϩ in a bidentate mode, complexes are stable up to 1 : 3 stoichiometry with L = TPPO and CMPO. From the 1 : 3 stoichiometry with bidentate nitrates, the interactions of the cation with water become repulsive, which facilitates the extraction from an aqueous to an organic phase. With TBP as ligand, 1 : 4 stoichiometry cannot be precluded, but formation of this complex appears to be kinetically more difficult than for the 1 : 3 complex.

Molecular Dynamics Simulation of Tri-n-butyl-Phosphate Liquid: A Force Field Comparative Study

“…The maximum dipole moment is predicted by the OPLS-MNDO parameter set, 4.93 ( 0.14 D, while the minimum is predicted by the OPLS-DFT force field, 3.80 ( 0.10 D. These higher values are consistent with other simulations which have reported p D = 4.84 D. 16 In fact, the suggestion is made that, in dense liquids, TBP molecules prefer conformations that are more extended than that of isolated molecules in a vacuum.…”

Importance of interfacial phenomena in assisted ion extraction by supercritical CO2: a molecular dynamics investigation

“…The CalixC6ÉCs`complex was simulated free of constraints, as according to MD simulations in an aqueous environment, the cation remains encapsulated.22 This turned out not to be the case for the and UO 2 (NO 3 ) 2 TBP 2 complexes which dissociate in water. 51 In Eu(NO 3 ) 3 TBP 3 order to prevent dissociation and to make these complexes as hydrophobic as possible, they were simulated at the interface with metalÈoxygen distances constrained to the corresponding values in the gas phase, with a force constant of 2.5 kcal mol~1 A ~2.…”

Solvation of uranyl–CMPO complexes in dry vs. humid forms of the [BMI][PF6] ionic liquid. A molecular dynamics study

“…[36][37][38] The charges and van der Waals parameters for UO 2 2+44 and NO 3 À45 were fitted using free energies of hydration, while those for CMPO were adapted from the CMPO analogue (replacing the C 8 H 17 phosphoryl substituent by phenyl, and N-isobutyl by N-butyl groups) studied in ref. 46. A summary of the atomic charges and AMBER atom types of the different solutes is given in Fig.…”