Supramolecular interactions of fullerenes with (Cl)Fe- and Mn porphyrins. A theoretical study

Abstract

The electronic structure and bonding in the noncovalent, supramolecular complexes of fullerenes (C₆₀, C₇₀) with (Cl)Fe- and Mn porphyrins [(Cl)FeP, MnP] were investigated in detail with DFT methods. A dispersion correction was made for the fullerene–porphyrin binding energy through an empirical approach. Several density functionals were employed in the calculations in order to obtain reliable results. Our calculated results differ from those obtained in a previous paper (J. Phys. Chem. A, 2005, 109, 3704). The ground state of (Cl)FeP·C₆₀ is predicted to be high spin (S = 5/2), in agreement with the experimental results. MnP·C₇₀ is calculated to have a high-spin (S = 5/2) ground state as well; this is similar to (Cl)FeP·C₆₀, but at variance with the assignment of a low-spin (S = 1/2) state for this complex. According to the calculations, C₇₀ in MnP·C₇₀ does not have sufficient ligand-field strength to cause a high- to low-spin state change in MnP. An additional calculation on a comparable, high-spin (Py)MnP complex gives support for the calculated results on MnP·C₇₀. More detailed experimental investigations are desirable, which might help to resolve the question of the MnP·C₇₀ electronic structure. The estimated dispersion energies (E_disp) in the fullerene–porphyrin systems are rather large, ranging from 0.6 to 1.0 eV. Including E_disp improves the calculated binding energy considerably.