Assessing Covalency in Cerium and Uranium Hexachlorides: A Correlated Wavefunction and Density Functional Theory Study

Abstract

The electronic structure of a series of uranium and cerium hexachlorides in a variety of oxidation states was evaluated at both the correlated wavefunction and density functional (DFT) levels of theory. Following recent experimental observations of covalency in tetravalent cerium hexachlorides, bonding character was studied using topological and integrated analysis based on the quantum theory of atoms in molecules (QTAIM). This analysis revealed that M-Cl covalency was strongly dependent on oxidation state, with greater covalency found in higher oxidation state complexes. Comparison of M-Cl delocalisation indices revealed a discrepancy between correlated wavefunction and DFT-derived values. Decomposition of these delocalisation indices demonstrated that the origin of this discrepancy lay in ungerade contributions associated with the f-manifold which we suggest is due to self-interaction error inherent to DFT-based methods. By all measures used in this study, extremely similar levels of covalency between complexes of U and Ce in the same oxidation state was found.

Quantification of f-element covalency through analysis of the electron density: insights from simulation

“…Few systematic density-based studies investigating the dependency of covalent bond character on metal oxidation state exist. Beekmeyer and Kerridge analysed DFT-, RASSCF and-CASSCFderived [UCl 6 ] nÀ (n = 0-3) densities 65 and determined that, while only weak covalency, as evidenced by r BCP and d(U,Cl) measures, was present, oxidation state dependence was pronounced, see Table 3. The authors found that, irrelevant of the simulation method used, covalent bond character was most pronounced in the highest (+6) oxidation state, with r BCP values for the lowest (+3) some 60% lower.…”

“…Beekmeyer and Kerridge have performed the same analysis to identify (n + 1)d and nf bonding contributions in [MCl 6 ] nÀ , where M = Ce and U. 65 Comparing DFT to RASSCF/CASSCF generated densities, they found that the former gave delocalisation indices consistently higher than the latter. However, the majority of this increase could be attributed to the ungerade (i.e.…”

Ceric Ammonium Nitrate and Ceric Ammonium Chloride as Precursors for Ceric Siloxides: Ammonia and Ammonium Inclusion

“…The Ce-O distances in five-coordinate 6(py) [2.101(1) -2.120(1) Å] are similar to those observed in seven-coordinate complex 3 or six-coordinate [Ce(OSiPh 3 ) 4 (DME)] [Ce-O Si 2.098(1) -2.133(1) Å], [5] but slightly shorter than found in the metallasilsesquioxane complex [Ce-{(c-C 6 H 11 ) 8 [25] Considering the different bonding in tetra-and trivalent cerium complexes, [55] an increasing contribution of π-backbonding between the non-bonding oxygen orbitals and to some degree stronger involved 5d and 4f-orbitals in Ce IV relative to Ce III complexes is expected. [32d, [55][56][57][58][59] Accordingly, 6(py) displays longer Si-O Ce bond lengths (ΔSi-O Ce : 0.030-0.034 Å) in comparison with 7, which is the result of weakened bonds due to an increase in π-backbonding within the Ce-O bond. As a consequence, also less bent Ce-O-Si bond angles are measured in the structure of the Ce IV complex.…”

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.…”