Theoretical insights into the structure of the η⁵-(Cp ^*)C⁺ cation

Using both ab initio and density functional theory (DFT) calculations in combination with basis sets of triple- and quadruple-ξ quality we investigate the molecular and electronic structure of the half-sandwich η⁵-(Cp^*)C⁺ cation. The results indicate that the lowest-energy rotamer is a C₅-symmetric ground state singlet while the triplet state is C_s-symmetric and ∼68 kcal/mol higher in energy. A topological analysis of the theoretical electron density based on the quantum theory of atoms in molecules (QTAIM) indicates that the η⁵-type bonding between the apical carbon atom and Cp ^* comprises five bond paths each bearing a bond critical point of type (3,-1).