X-ray structural and DFT computational studies of a self-assembled via axial coordination magnesium porphyrin-fullerene conjugate

Slow evaporation of a mixture of organic solvents containing meso-tetraphenylporphyrinato-magnesium(II), MgTPP and N-methyl-2-(4'-N-imidazolylphenyl)-fulleropyrrolidine, C60Im yielded, air stable, dark purple crystals. Determination of the structure by single crystal X-ray diffraction revealed two forms of slightly varying self-assembled via axial coordination MgTPP:C60Im dyad. The Mg-N distance of the newly formed coordinate bond was found to be 2.131 A which was close to the porphyrin ring Mg-N bond distances. The edge-to-edge distances were found to be 9.024 and 9.269 A, respectively, for the two structure forms. The center-to-center distance between the magnesium and fullerene was 13.296 A irrespective of the structural forms. Additional intermolecular type interactions between the magnesium porphyrin and fullerene entities that are not axially coordinated were also observed. DFT calculations performed at the B3LYP/3-21G(*) level on the fullerene and porphyrin segments suggested that the charge transfer type π–π interactions are primarily responsible for the intermolecular association of the presently studied donor-acceptor dyad.