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 (C(60), C(70)) 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*C(60) is predicted to be high spin (S = 5/2), in agreement with the experimental results. MnP*C(70) is calculated to have a high-spin (S = 5/2) ground state as well; this is similar to (Cl)FeP*C(60), but at variance with the assignment of a low-spin (S = 1/2) state for this complex. According to the calculations, C(70) in MnP*C(70) 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*C(70). More detailed experimental investigations are desirable, which might help to resolve the question of the MnP*C(70) 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.