The strength of actinide–element bonds from the quantum theory of atoms-in-molecules

Abstract

[AnX(3)](2)(μ-η(2):η(2)-N(2)) (An = Th-Pu; X = F, Cl, Br, Me, H, OPh) have been studied using relativistic density functional theory. Geometric and vibrational data suggest that metal→N(2) charge transfer maximises at the protactinium systems, which feature the longest N-N bonds and the smallest σ(N-N), as a result of partial population of the N-N π* orbitals. There is very strong correlation of the standard quantum theory of atoms-in-molecules (QTAIM) metrics - bond critical point ρ, ∇(2)ρ and H and delocalisation indices - with An-N and N-N bond lengths and σ(N-N), but the correlation with An-N interaction energies is very poor. A similar situation exists for the other systems studied; neutral and cationic actinide monoxide and dioxides, and AnL(3+) and AnL(3)(3+) (L = pyridine (Py), pyrazine (Pz) and triazine (Tz)) with the exception of some of the ∇(2)ρ data, for which moderate to good correlations with energy data are sometimes seen. By contrast, in almost all cases there is very strong correlation of interaction and bond energies with |ΔQ(QTAIM)(An)|, a simple QTAIM metric which measures the amount of charge transferred to or from the actinide on compound formation.

Computational analysis of M–O covalency in M(OC6H5)4(M = Ti, Zr, Hf, Ce, Th, U)

“…The metrics employed herein have been used extensively to characterize bonding in situ and have been shown to be particularly useful in f element chemistry. 4,31,[36][37][38][39] Data for the bond critical point (BCP) metrics (electron density, ρBCP, its Laplacian ∇ 2 ρBCP, and the total energy density HBCP) and integrated QTAIM properties (atomic charge, q, and the delocalization index of the M and O atom pair, δ(M,O)) are shown in Table 2 for the optimized M(OC6H5)4 systems (and for the systems at r(M-O) -0.12 Å in Table SI2 of the Supplementary Information). The magnitudes of ρBCP and HBCP are measures of covalency, where values of ρBCP > 0.2 au and HBCP < 0 indicate interactions with significant sharing of electrons, or covalent character.…”

Should environmental effects be included when performing QTAIM calculations on actinide systems? A comparison of QTAIM metrics for Cs2UO2Cl4, U(Se2PPh2)4 and Np(Se2PPh2)4 in gas phase, COSMO and PEECM

“…This is due partly to the experimental difficulties associated with obtaining high quality experimental electron densities on radioactive systems featuring very heavy elements, and partly a function of the QTAIM only recently being extended to quantum chemical studies of the actinide elements. Indeed, we were the first group to extensively employ the QTAIM in this capacity, and have used it to study both covalency [6][7][8][9][10][11][12][13][14][15][16][17][18] and bond strength [19][20][21] in a range of molecular f element systems.…”

Structure and separation quality of various N- and O-donor ligands from quantum-chemical calculations

“…Considerable progress has been made, however, in understanding particular parts of the ligands' properties like structure, solubility and solvent infl uence studied by a variety of setups including nuclear magnetic resonance (NMR), time--resolved laser fl uorescence spectroscopy (TRLFS), UV-Vis and extended X-ray absorption fi ne structure (EXAFS) [1][2][3][4][5]. Also theoretical studies tried to shed light into the complex actinide-nitrogen bond [6][7][8][9][10][11][12][13], but due to the large system size one is often restricted to DFT or simplifi ed model systems treating the aromatic rings separately. Description of the solvent in quantum-chemical (QM) calculations is rather demanding as it introduces many new degrees of freedom and adds even more to the number of explicitely treated atoms, whereas results using polarizable continuum models to mimic the solvent have to be treated with care when the cavity is too close to the highly charged metal ions.…”