Charge separation (coulomb explosion) processes of doubly charged cations of sandwich compounds in the gas phase: evidence for the junction of two C₅H₅ units

The charge separation reactions (coulomb explosion) of the ferrocene, cobaltocene, and nickelocene dications, generated by electron impact ionization in the gas phase, are reported. These sandwich dications display a common behaviour in their unimolecular decomposition reactions, which are characterized by two distinct charge separation pathways. One corresponds to the reaction [MC₁₀H₁₀]²⁺ → [MC₅H₅]⁺ + C₅H₅ ⁺, and the other to the generation of C₁₀H₁₀ ^{+{radical dot}} and M⁺ (M Fe, Co, Ni). From the translational energy releases, associated with the charge separation processes, the intercharge distances of the exploding dications in their transition structures have been calculated. The results demonstrate that, irrespective of the nature of the transition metal ion M, the interchange distance for the formation of [MC₅H₅]⁺/C₅H⁺ ₅ is 5.0 Å and 6.2 Å for the generation of C₁₀H⁺ ₁₀ and M⁺.