Theoretical studies of organometallic compounds. III. Structures and bond energies of FeCH_n and FeCH n+ (n = 1, 2, 3)

The geometries and dissociation energies for the FeC and CH bonds of FeCH_n and FeCH n+ (n = 1, 2, 3) have been calculated by ab initio quantum mechanical methods using different effective core potential models and Møller–Plesset perturbation theory. The HW3 ECP model, which has a configuration [core] (n−1)s², (n−1)p⁶, (n−1)d¹, (n)s^m for the transition metals, is clearly superior to the larger core LANL1DZ ECP model with the configuration [core] (n−1)d¹, (n)s^m. The FeC bond energies calculated at correlated levels using the HW3 ECP are in much better agreement with experiment than the LANL1DZ results. This effect is mainly due to the higher number of correlated electrons rather than the inclusion of the outermost core electrons in the Hartree–Fock calculation. At the PMP4/HW3TZ/6‐31G(d)//MP2/HW3TZ/6‐31G(d) level, the theoretically predicted FeC bond energies for FeCH n+ are in the range of 80% of the experimental values and have nearly the same accuracy as all‐electron calculations using large valence basis sets and the MCPF method for the correlation energy. © 1992 by John Wiley & Sons, Inc.