Multi-decker tricarbonyl-bridged sandwich complexes of transition metals: structure, stability and electron-counting rules.

Structures and stabilities of a new family of multi-decker tricarbonyl-bridged sandwich complexes of transition metals (Cr, Mn, Fe) have been studied using DFT B3LYP/6-311+G(df,p) calculations. Stable structures satisfy the (12n + 6) electron-counting rule, where n is the number of metal atoms. Lengthening of the molecular chains is accompanied by growth of aromaticity of the inner basal cycles, lowering of the aromaticity of the terminal basal cycles and decrease in the energy gap between the frontier orbitals.