A Multiconfigurational Perturbation Theory and Density Functional Theory Study on the Heterolytic Dissociation Enthalpy of First-Row Metallocenes.

The heterolytic dissociation enthalpy of a series of first-row metallocenes M(C5H5)2, M = V, Mn, Fe, and Ni, was studied by (restricted) multiconfigurational perturbation theory and density functional theory. The results were compared directly to the experimental values, taking into account all necessary contributions to the relative energy. Of the tested functionals, B3LYP performs best in reproducing the binding energy, while the PBE0 functional gives the best structures. High quality multiconfigurational perturbation calculations were also carried out, demonstrating the superior performance of a larger, restricted active space. The spin crossover behavior of manganocene is correctly predicted by multiconfigurational perturbation theory as opposed to the three functionals B3LYP, PBE0, and M06, which (severely) overstabilize the high-spin with respect to the low-spin state.