ELECTRONIC STRUCTURE OF F(1) ACTINIDE COMPLEXES .1. NONRELATIVISTIC AND RELATIVISTIC CALCULATIONS OF THE OPTICAL TRANSITION ENERGIES OF ANX(6)(Q-) COMPLEXES

摘要

The ground-state electronic structures of PaX(6)(2-) (X = F, Cl, Br, I), UX(6)(-) (X = F, Cl, Br), and NpF6 have been calculated, using both nonrelativistic and relativistic implementations of the discrete-variational X alpha (DV-X alpha) method. A significant amount of metal-ligand covalent bonding is found, involving both 6d and 5f metal orbitals. The 5f contribution to the bonding levels increases significantly from PaX(6)(2-) to UX(6)(-) to NpF6 but remains approximately constant as the halogen is altered in PaX(6)(2-) and UX(6)(-). In contrast, the 6d atomic orbital character of the halogen-based levels increases from UF6- to UBr6- and a similar, though less marked, trend is observed in PaX(6)(2-). The electronic transition energies have been calculated using the transition state method. The relativistic calculations are far superior to the nonrelativistic ones in both qualitatively and quantitatively describing the electronic spectra. The stabilization of the metal 5f atomic orbitals with respect to the halogen np levels from protactinium to neptunium results in the more energetic f --> f transitions in NpF6 being masked by the onset of a ligand-to-metal charge-transfer band. In the remaining molecules, the f --> f transitions occur well removed from charge-transfer bands. [References: 50]