Periodic trends and complexation chemistry of tetravalent actinide ions with a potential actinide decorporation agent 5‐LIO(Me‐3,2‐HOPO): A relativistic density functional theory exploration

Abstract

A relativistic density functional theory (DFT) study is reported which aims to understand the complexation chemistry of An 4+ ions (An = Th, U, Np, and Pu) with a potential decorporation agent, 5-LIO(Me-3,2-HOPO). The calculations show that the periodic change of the metal binding free energy has an excellent correlation with the ionic radii and such change of ionic radii also leads to the structural modulation of actinide-ligand complexes. The calculated structural and binding parameters agree well with the available experimental data. Atomic charges derived from quantum theory of atoms in molecules (QTAIM) and natural bond order (NBO) analysis shows the major role of ligand-to-metal charge transfer in the stability of the complexes. Energy decomposition analysis, QTAIM, and electron localization function (ELF) predict that the actinide-ligand bond is dominantly ionic, but the contribution of orbital interaction is considerable and increases from Th 4+ to Pu 4+ . A decomposition of orbital contributions applying the extended transition state-natural orbital chemical valence method points out the significant π-donation from the oxygen donor centers to the electron-poor actinide ion. Molecular orbital analysis suggests an increasing trend of orbital mixing in the context of 5f orbital participation across the tetravalent An series (Th-Pu). However, the corresponding overlap integral is found to be smaller than in the case of 6d orbital participation. An analysis of the results from the aforementioned electronic structure methods indicates that such orbital participation possibly arises due to the energy matching of ligand and metal orbitals and carries the signature of near-degeneracy driven covalency. K E Y W O R D S actinide, covalency, decorporation agent, density functional theory, ETS-NOCV, QTAIM

Charge Density Analysis of Actinide Compounds from the Quantum Theory of Atoms in Molecules and Crystals

“…However, the accurate description of the charge density of actinide compounds is challenging also from a theoretical perspective as one needs to (i) account for relativistic effects, (ii) consider strong electron correlation, (iii) describe the correct localization/delocalization of 5 f and 6 d orbitals, and (iv) provide enough variational freedom through a rich and angularly flexible basis set. Recently, the QTAIMAC started being applied to the quantum-mechanical study of chemical bonding in molecular actinide complexes. − In particular, Gianopoulos et al . , computed the charge density of the UF 6 – molecular fragment extracted from the [PPh 4 + ]­[UF 6 – ] crystal, performed a QTAIMAC study, and compared their theoretical results with those from the experiment on the crystals. While an overall agreement between the molecular calculations and the experiments on the crystal was observed for some features of the chemical bonding, some significant quantitative, and even qualitative, discrepancies remained, which require further analysis.…”

Topology of the Electron Density and of Its Laplacian from Periodic LCAO Calculations on f-Electron Materials: The Case of Cesium Uranyl Chloride

“…In the periodic calculations, reciprocal space is sampled on a regular 6×6×6 Monkhorst-Pack grid, corresponding to 68 k -points in the symmetry-irreducible Brillouin zone. Scalar relativistic effects of U must be accounted for [ 27 , 28 , 29 , 41 ] and, here, are described by use of small-core effective pseudopotentials, ECP60MDF (with 60 electrons in the core for U) [ 42 , 43 ]. The valence of U is described by a (10 s 9 p 7 d 5 f 1 g )/[10 s 9 p 7 d 5 f 1 g ] basis set: we indicate within round brackets the number of Gaussian primitive functions used for the various angular quantum numbers and within square brackets the number of shells in which they are contracted.…”

“…In particular, significant advances have been recently reported by Pinkerton and co-workers on data collection and analysis, which finally allow for the accurate experimental determination of the electron density of actinide materials [ 21 ]. Similarly, from a theoretical perspective, the many challenges related to a proper and simultaneous description of relativistic effects of core electrons and electron correlation of valence electrons (including f -type ones) made it possible to perform a QTAIM analysis on top of computed electron densities of actinide molecular complexes only recently [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ].…”

Covalency in actinide(iv) hexachlorides in relation to the chlorine K-edge X-ray absorption structure

“…Such knowledge is of paramount importance for a wide range of applications, including the development of Ln and An-based single-molecule magnets, [1][2][3][4][5][6] metal-organic frameworks, [7][8][9][10][11] endohedral metallofullerenes, [12][13][14][15][16][17] nanoparticles for industrial catalytic reactions and biomedicine, 18 and the design of chelating ligands for f-element separation. [19][20][21][22][23] Rational design of new f-element materials and separation ligands requires knowledge of the ionic vs. covalent behavior of the Ln 4f/5f and An 5f/6d shells. The development of computational tools for exploring the peculiar electronic structure of the heaviest elements is a key component of this research.…”