Structures, bond energies, heats of formation, and quantitative bonding analysis of main-group metallocenes [E(Cp)2] (E = Be-Ba, Zn, Si-Pb) and [E(Cp)] (E = Li-Cs, B-Tl).

The geometries, metal-ligand bond dissociation energies, and heats of formation of twenty sandwich and half-sandwich complexes of the main-group elements of Groups 1, 2, 13, and 14, and Zn have been calculated with quantum chemical methods. The geometries of the [E(Cp)] and [E(Cp)2] complexes were optimized using density functional theory at the BP86 level with valence basis sets, which have DZP and TZP quality. Improved energy values have been obtained by using coupled-cluster theory at the CCSD(T) level. The nature of the metal-ligand bonding has been analyzed with an energy-partitioning method. The results give quantitative information about the strength of the covalent and electrostatic interactions between En+ and (Cp-)n (n = 1, 2). The contributions of the orbitals with different symmetry to the covalent bonding are also given.