Chemical applications of topology and group theory. 27. Covalent bonding in actinide derivatives

Abstract

The d-block transition metals are characterized by forming strong cvalent bonds involving the d orbitals in a nine-orbital spherical sp[sup 3]d[sup 5] manifold thereby leading to the familiar 18-electron rule for the stable electronic configurations of transition metal coordination and organometallic complexes. On the other hand the 4f orbitals in the lanthanides appear to participate very little in covalent bond formation so that the chemistry of the lanthanides is governed largely by electrostatic considerations similar to the chemistry of the alkali and alkaline earth metals but with a predominant +3 oxidation state. The chemistry of the actinides from at least uranium through americium exhibits some features of both the predominantly covalent bonding of the d-block transition metals and the predominantly electrostatic bonding of the lanthanides since both the 5f and 6d orbitals of the actinides can function as valence orbitals leading to an unusual 12-orbital spherical d[sup 5]f[sup 7] manifold. This paper uses elementary group theory to explore how such a d[sup 5]f[sup 7] manifold can participate in the types of covalent bonding prevalent in actinide chemistry.