Mixed Uranium Chloride Fluorides UF_6-nCl_nand Methoxyuranium Fluorides UF_6-n(OCH₃)_n:  A Theoretical Study of Equilibrium Geometries, Vibrational Frequencies, and the Role of the f Orbitals

Abstract

The title compounds, the uranium (VI) fluoride chlorides (UF6-nCln, n = 0-6) and methoxyuranium (VI) fluorides [UF6-n(OCH3)n, n = 0-5], have been studied using relativistic density functional theory. Applying the B3LYP hybrid functional and an effective core potential on uranium, equilibrium geometries have been calculated for these molecules. In addition, harmonic vibrational frequencies have been computed for the chloride fluorides. Calculated frequencies have been compared to experiment where possible. All experimentally observed bands have been assigned, based on these calculations. The average deviation between theoretical and experimental frequencies is 15.6 cm-1 for 23 experimental modes. Theory always underestimates the experimental frequencies. This can be explained by the calculated bond lengths that are somewhat too long. The electronic structure of the uranium (VI) chloride fluorides has been investigated using scalar relativistic calculations and the PW91 functional. Periodic trends in the role and bonding contribution of the uranium 5f orbitals are discussed.

A Theoretical Study of the Structure and Bonding of UOX4(X=F, Cl, Br, I) Molecules: The Importance of InverseTransInfluence

“…pounds. [7,35,60,61] Moreover, for the C 3v and C 2v structures of the molecules studied, the QR-BP/TZP geometrical parameters are very close to those obtained from the (probably most reliable) MP2 calculations, closer than the B3PW ones! Nevertheless, the above results show that the BP functional should be used with caution in actinide research.…”

“…The quadrupolar polarisation of the U electron-density distribution can also be expected on the UÀhalogen bond. We found in the literature two papers reporting the computed molecular geometry of UCl 5 F. [61,64] The authors obtained somewhat shorter UÀCl bonds trans to F with respect to the UÀCl bond trans to Cl. Depending on the level of theory used, the differences amounted to 0.4-0.8 pm.…”

A Comparative Relativistic DFT and Ab Initio Study on the Structure and Thermodynamics of the Oxofluorides of Uranium(IV), (V) and (VI)

“…[17] and [18] and references therein). Batista et al [19] investigated the lower uranium fluorides, UF 5 and UF 4 , [18] in their benchmark study of the UF n bond dissociation energies (BDE).…”

Density functional investigations of the properties and thermochemistry of UFn and UCln (n=1,…,6)

“…While uranium hexafluoride UF 6 is one of the most extensively studied actinide molecules, 1 both experimentally and theoretically, very few computational studies have been reported on the rest of the fluoride series UF n or on the uranium chlorides UCl n .…”

“…The UF 6 molecule, even though it is the largest and has the most electrons, is the easiest one to study with ab initio calculations because of its closed shell nature. This molecule has been studied by many authors with a variety of computational techniques 1,[13][14][15][16][17][18] so that it has become a testing benchmark for computational methods aimed at actinide molecules. A study of the electronic structure of UF 4 has been reported using HartreeFock-Slater type calculations 19 with scalar relativistic pseudopotentials.…”