Interaction of metal porphyrins with fullerene C60: a new insight

The electronic structure and bonding in the noncovalent, supramolecular complexes of fullerene C60 with a series of first-row transition metal porphines MP (M=Fe, Co, Ni, Cu, Zn) have been re-examined with DFT methods. A dispersion correction was made for the C60-MP binding energy through an empirical method (J. Comput. Chem. 2004, 25, 1463). Several density functionals and two types of basis sets were employed in the calculations. Our calculated results are rather different from those obtained in a recent paper (J. Phys. Chem. A 2005, 109, 3704). The ground state of C60.FeP is predicted to be high spin (S=2); the low-spin (S=0), closed-shell state is even higher in energy than the intermediate-spin (S=1) state. With only one electron in the Co-dz2 orbital, the calculated Co-C60 distance is in fact rather short, about 0.1 A longer than the Fe-C60 distance in high-spin C60.FeP. Double occupation of an M-dz2 orbital in MP prevents close association of any axial ligand, and so the Ni-C60, Cu-C60, and Zn-C60 distances are much longer than the Co-C60 one. The evaluated MP-C60 binding energies (Ebind) are 0.8 eV (18.5 kcal/mol) for M=Fe/Co and 0.5 eV (11.5 kcal/mol) for M=Ni/Cu/Zn (Ebind is about 0.2 eV larger in the case of C60-MTPP). They are believed to be reliable and accurate based on our dispersion-corrected DFT calculations that included the counterpoise (CP) correction. The effects of the C60 contact on the redox properties of MP were also examined.