THEORETICAL-STUDY OF THE CHEMICAL BONDING IN NI(C2H4) AND FERROCENE

The equilibrium structure and bond energies of the transition-metal complexes Ni(C2H4) and ferrocene have been studied by using the complete active space (CAS)SCF method and second-order perturbation theory (CASPT2). It is shown that the major features of the electronic structure are properly described by a CASSCF wavefunction based on an active space comprising the bonding and antibonding orbitals directly involved in the metal-ligand bond. Remaining correlation effects are dealt with in the second, CASPT2, step. The computed energies have been corrected for BSSE and relativistic corrections have been added. Resulting bond distances and bond energies are in agreement with experimental data, when available. Ni(C2H4): r(C - C) = 1.443 Angstrom, r(Ni-C) 1.868 Angstrom, D-e = 32.3 (36.4 +/- 5) kcal/mol. Ferrocene: r(Fe-ring) = 1.643 (1.66)Angstrom, D-e = 156 (157 +/- 3) kcal/mol (experimental values within parentheses).