Selectivity of bis-triazinyl bipyridine ligands for americium(iii) in Am/Eu separation by solvent extraction. Part 1. Quantum mechanical study on the structures of BTBP complexes and on the energy of the separation
- 9 October 2012
- journal article
- Published by Royal Society of Chemistry (RSC) in Dalton Transactions
- Vol. 41 (47), 14416-14424
- https://doi.org/10.1039/c2dt31503c
Abstract
Theoretical studies were carried out on two pairs of americium and europium complexes formed by tetra-N-dentate lipophilic BTBP ligands, neutral [ML(NO3)3] and cationic [ML2]3+ where M = AmIII or EuIII, and L = 6,6′-bis-(5,6-diethyl-1,2,4-triazin-3-yl)-2,2′-bipyridine (C2-BTBP). Molecular structures of the complexes have been optimized at the B3LYP/6-31G(d) level and total energies of the complexes in various media were estimated using single point calculations performed at the B3LYP/6-311G(d,p) and MP2/6-311G(d,p) levels of theory. In the calculations americium and europium ions were treated using pseudo-relativistic Stuttgart–Dresden effective core potentials and the accompanying basis sets. Selectivity in solvent extraction separation of two metal ions is a co-operative function of contributions from all extractable metal complexes, which depend on physico-chemical properties of each individual complex and on its relative amount in the system. Semi-quantitative analysis of BTBP selectivity in the Am/Eu separation process, based on the contributions from the two pairs of AmIII and EuIII complexes, has been carried out. To calculate the energy of Am/Eu separation, a model of the extraction process was used, consisting of complex formation in water and transfer of the formed complex to the organic phase. Under the assumptions discussed in the paper, this simple two-step model results in reliable values of the calculated differences in the energy changes for each pair of the Am/Eu complexes in both steps of the process. The greater thermodynamic stability (in water) of the Am–BTBP complexes, as compared with the analogous Eu species, caused by greater covalency of the Am–N than Eu–N bonds, is most likely the main reason for BTBP selectivity in the separation of the two metal ions. The other potential reason, i.e. differences in lipophilic properties of the analogous complexes of Am and Eu, is less important with regard to this selectivity.Keywords
This publication has 44 references indexed in Scilit:
- A TRLFS Study on the Complexation of CmIII and EuIII with 2,6‐Bis(5,6‐dipropyl‐1,2,4‐triazin‐3‐yl)pyridine in Water/Methanol MixtureEuropean Journal of Inorganic Chemistry, 2010
- Direct nano ESI time-of-flight mass spectrometric investigations on lanthanide BTP complexes in the extraction-relevant diluent 1-octanolNew Journal of Chemistry, 2009
- Complexation and Separation of Lanthanides(III) and Actinides(III) by Heterocyclic N-Donors in SolutionsChemical Reviews, 2008
- A comparative spectroscopic study of U(III)/Am(III) and Ln(III) complexed with N-donor ligandsComptes Rendus. Chimie, 2007
- Actinide(III) and lanthanide(III) complexes with nitrogen ligands: Counterions and ligand substituent effects on the metal–ligand bondJournal of Molecular Structure: THEOCHEM, 2006
- Relativistic energy-consistent ab initio pseudopotentials as tools for quantum chemical investigations of actinide systemsCoordination Chemistry Reviews, 2006
- Actinide Chemistry in Solution, Quantum Chemical Methods and ModelsTheoretical Chemistry Accounts, 2006
- Characterization and Comparison of Cm(III) and Eu(III) Complexed with 2,6-Di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine Using EXAFS, TRFLS, and Quantum-Chemical MethodsInorganic Chemistry, 2005
- Thermodynamic Study of the Complexation of Trivalent Actinide and Lanthanide Cations by ADPTZ, a Tridentate N-Donor LigandInorganic Chemistry, 2005
- Quantum Chemistry Study of Actinide(III) and Lanthanide(III) Complexes with Tridentate Nitrogen LigandsThe Journal of Physical Chemistry A, 2004