DFT modeling of the relative affinity of nitrogen ligands for trivalent f elements: an energetic point of view

Abstract

aIn many theoretical studies dealing with the selective complexation of trivalent actinides with respect to trivalent lanthanides, the method of calculation is assessed by comparing computed geometries with crystal structures that are often available. Yet, the selectivity is better rationalized through thermodynamic data, as enthalpy and entropy terms. In this article, we have theoretically modeled competing complexation reactions of [Ce(terpy) 3+ systems (terpy = 2,2 0 :6 0 2 00 -terpyridine; MeBTP = methyl-2,6-di(1,2,4-triazin-3-yl)pyridine) within the framework of the Density Functional Theory. Our calculations manage to qualitatively account for the experimental relative stabilities of terpy and MeBTP complexes, and in particular for the better coordinating strength of MeBTP for trivalent uranium. We also show by comparing the MeBTP ligand with its non-alkylated form (HBTP) that model systems often used in quantum chemistry must be carefully chosen when energetic comparisons are undertaken.

Insights into the Extraction of Actinides from Lanthanides Using 3,3’‐Dimethoxy‐phenyl‐bis‐1,2,4‐triazinyl‐2,6‐pyridine Ligand – A DFT Study

“…Out of these ligands, terpyridine (terpy), [10] BTP (2,6‐bis(1,2,4‐triazin‐3‐yl)pyridine), [11] tpza (tris[(2‐ pyrazinyl)methyl]amine) [12] and tptz (2,4,6‐tris(4‐alkyl‐2‐pyridyl)‐ 1,3,5‐triazine) [13] are Lewis bases with significance in the Ln/An separation. Earlier report suggests that the BTP ligands are found to disclose better extraction capability in comparison with the terpy ligands [14] …”

Hindered rotation in a novel 1,2,4-triazinyl phenanthroline (t-phen) ligand leading to improved separation of Am3+ and Eu3+vis-à-vis 1,2,4-triazinyl bipyridine (t-bipy): a computational validation of the experimental results

“…The alkyl substituents show insignificant changes in the charge distributions and the energy gap between the frontier orbitals. 13 A number of studies were also carried out, where H-form of BTP was considered as a model for the alkyl BTP derivatives. 14,15 Most of the calculations of the free ligands and their Am 3+ and Eu 3+ complexes were, therefore, performed for hydrogen form of both the ligands (t-bipy and t-phen).…”

“…The HOMO-LUMO gap is considered to be proportional to the absolute hardness. 30,31 The lower HOMO-LUMO gap of t-phen, therefore, makes it softer than t-bipy. The higher selectivity of t-phen for Am 3+ over Eu 3+ as compared to t-bipy, as observed from the solvent extraction studies (Fig.…”

Development of highly selective compounds for solvent extraction processes: partitioning and transmutation of long-lived radionuclides from spent nuclear fuels

“…On a more fundamental level, quantum chemistry and molecular dynamics calculations, such as density functional theory, have been used concomitantly with structural and spectroscopic characterization to enrich basic knowledge of actinide complex formation and/or extraction (Boehme and Wipff, 1999a,b, Karmazin et al, 2002, Baaden et al, 2003, Coupez et al, 2003. Beyond the diffi culties of characterizing the radioactive systems investigated, this modelling approach seeks to defi ne independent physical criteria that can be experimentally observed at different scales (molecular, microscopic as well as macroscopic) and correlated with modelling calculations (Guillaumont et al, 2006, Petit et al, 2007, Gaunt et al, 2008. (ii) Small quantities (sometimes a few hundred milligrams) of the desired compound are synthesized and chemically characterized to validate its structure and determine its purity utilizing suitable analytical tools such as nuclear magnetic resonance (NMR), mass spectrometry or elementary analysis.…”