Abstract
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.

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