Metal-metal bonding in molecular actinide compounds: electronic structure of [M 2 X 8 ] 2- (M = U, Np, Pu; X = Cl, Br, I) complexes and comparison with d-block analogues

Abstract

Density functional and multiconfigurational (ab initio) calculations have been performed on [M2X8]2- (X = Cl, Br, I) complexes of 4d (Mo, Tc, Ru), 5d (W, Re, Os), and 5f (U, Np, Pu) metals in order to investigate general trends, similarities and differences in the electronic structure and metal-metal bonding between f-block and d-block elements. Multiple metal-metal bonds consisting of a combination of σ and π interactions have been found in all species investigated, with δ-like interactions also occurring in the complexes of Tc, Re, Np, Ru, Os, and Pu. The molecular orbital analysis indicates that these metal-metal interactions possess predominantly dz2 (σ), dxz and dyz (π), or d xy and dx2-y2 (δ) character in the d-block species, and fz3 (σ), fz2x and fz2y (π), or fxyz and fz (δ) character in the actinide systems. In the latter, all three (σ, π, δ) types of interaction exhibit bonding character, irrespective of whether the molecular symmetry is D 4h or D4d. By contrast, although the nature and properties of the σ and π bonds are largely similar for the D4h and D4d forms of the d-block complexes, the two most relevant metal-metal δ-like orbitals occur as a bonding and antibonding combination in D 4h symmetry but as a nonbonding level in D4d symmetry. Multiconfigurational calculations have been performed on a subset of the actinide complexes, and show that a single electronic configuration plays a dominant role and corresponds to the lowest-energy configuration obtained using density functional theory. Show more