A theoretical study on interaction of cyclopentadienyl ligand with alkali and alkaline earth metals

Ab initio and density functional theory calculations are performed on half-sandwich (M-Cp) and sandwich (Cp-M-Cp) complexes of alkali and alkaline earth metals (M = Li, Na, K, Mg, and Ca) with cyclopentadienyl ligand (Cp). A comparison of dissociation energies demonstrates the ease of dissociation of the complex as ions in solvent phase and preference for dissociation as radicals in gas phase. Atoms in molecules analysis is used to characterize this cation-π interaction based on electron density values obtained at the cage critical point. The contribution of various components to the complex energy is estimated using reduced variational space analysis confirming maximum contribution from the coulomb exchange followed by contributions from polarization and charge transfer components of cyclopentadienyl ligand.