THE PECULIAR ELECTRONIC STRUCTURE OF THE DI-METALLOCENE: THE EVIDENCE FOR THE STABILITY AND THE CHARACTER OF METAL–METAL BOND

Abstract

Quantum chemical density functional theory (DFT) calculations using B3LYP and BP86 functionals have been carried out for the di-metallocene complexes. The equilibrium geometries and the bond characters have been reported. The calculations of Cp 2 Zn 2, Cp 2 Cd 2 and Cp 2 Hg 2 demonstrate that the di-metallocene complexes slightly favor D 5 h conformations for the free molecules, where Cp is C 5 H 5. The predicted Cd-Cd distance of 2.723 Å and Hg-Hg distance of 2.826 Å are indicative of substantial Cd-Cd and Hg-Hg bonds. In this work, we have reported DFT MO energy level diagrams for the di-metallocene complexes. The strong interaction between Cp and Zn atoms is mainly due to the π orbital of the Cp and the s and dz2 orbitals of the Zn atom. The metal–metal bonds were studied in detail. The results indicated that there are two δ, one σ and two π interactions between five d orbitals and one σ interaction between s orbitals of the two metal atoms. The electron configurations are pictured as [Formula: see text], and so the bond order is determined by the molecular orbital theory, which is in agreement with the NBO analysis that shows that each metal atom has one covalent bond (to the other metal atom) and a nearly pure s character of metal–metal bonds. At last, from the behavior of the HOMO and HOMO-LUMO gap, the order of the stability of those di-metallocene complexes is Cp 2 Zn 2 > Cp 2 Cd 2 > Cp 2 Hg 2.