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

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 (Edisp) in the fullerene–porphyrin systems are rather large, ranging from 0.6 to 1.0 eV. Including Edisp improves the calculated binding energy considerably.