Covalency effects on the ligand field splittings of octahedral 5f7 compounds

Optical spectm were recorded for (NEt/sub 4/)/sub 2/PaCl/sub 6/ and (NEt/ sub 4/)PaBr/sub 6/ two ligand field parameters and the spin- orbit coupling constant. Similar interpretations are provided for data available on uranium (V)- hexahalogeno complexes and NpF/sub 6/. Trends in the ligand field parameters can be explained qualitatively in terms of molecular orbital theory with large variations in sigma bonding dominating the total ligand field splittings as the halide ion is varied. (auth)