Theoretical study of UX6 and UO2X2 (X = f, cl, br, I)

In the present study the structural, vibrational and bonding properties of the uranium(VI) halide and oxyhalide molecules UX6 and UO2X2 (X = F, Cl, Br, 1) have been investigated by quantum chemical calculations. The title molecular properties have been computed using quasi-relativistic density functional theory in conjunction with a polarised triple-zeta basis set. The bonding interactions between the fragments U...X-6 and UO2... X-2 have been investigated using the extended transition state energy partitioning method. Our quantitative analysis revealed an increase of the electrostatic interactions in UO2X2 with respect to UX6 as a result of the oxygen substitution. Analogously to previous results on uranyl, the bonding Kohn-Sham orbitals Of UO2X2 showed a clear triple-bond character of the formally U=O double bonds. The population analysis results are in agreement with a predominant role of the uranium 5f orbitals in the orbital interactions, whereas a slight strengthening of the 6d contributions toward the heavier halides. (C) 2004 Elsevier B.V. All rights reserved.