Porphyrin−Fullerene, C₆₀, Cocrystallates: Influence of C₆₀ on the Porphyrin Ring Conformation

To examine the influence of fullerene on the macrocyclic ring conformation, crystal structures of a series of cocrystals of 2,3,5,10,12,13,15,20-octaphenylporphyrin, M(TPP)(Ph)₄ (M = 2H, Co(II), Cu(II)), and 2,312,13-tetramethyl-5,7,8,10,15,17,18,20-octaphenyl-porphinato copper(II), CuTPP(Ph)₄(CH₃)₄, derivatives with fullerene, C₆₀, were elucidated. Furthermore, crystal structures of the parent porphyrins, M(TPP)(Ph)₄ (M = Co(II), Cu(II)) complexes, were also determined. All the cocrystals revealed one-to-one stoichiometry between the porphyrin and C₆₀ and were free of lattice solvates. Porphyrin rings in M(TPP)(Ph)₄·C₆₀ cocrystals revealed significant distortion with the root-mean-square (rms) value as high as 0.265(2) Å which is the average deviation of the 24 atoms core from the least-squares plane. Crystal structures of the parent M(TPP)(Ph)₄ (M = Co(II), Cu(II)) complexes indicated near planarity of the 24-atom core with the root-mean-square deviation value of 0.016(2) Å. Molecular packing in the M(TPP)(Ph)₄·C₆₀ cocrystals showed essentially one-dimensional chains interconnected by weak interporphyrin and porphyrin−fullerene close contacts. The N_porphyrin···C(C₆₀) shortest distances between the H₂(TPP)(Ph)₄ (M = 2H, Co(II), Cu(II)) and fullerene in the cocrystals are 3.031(5) Å, 3.062(4) Å, and 3.059(3) Å, respectively. Similarly, close contact M···C distances in the M(TPP)(Ph)₄·C₆₀ (M = Co(II), Cu(II)) are 2.761(6) Å and 2.886(3) Å, respectively. In the Cu(TPP)(Ph)₄(CH₃)₄·C₆₀ cocrystal, the shift of macrocyclic ring toward planarity was evidenced from the rms value of 0.236(2) Å relative to that observed in CuTPP(Ph)₄(CH₃)₄·CHCl₃ (0.391(2) Å). The distortion of the macrocyclic ring in M(TPP)(Ph)₄·C₆₀ complexes was examined by normal-coordinate-structure decomposition (NSD) analyses. Their out-of-plane displacement of the core atoms revealed predominant contribution being saddle (∼95−96%) and gentle domed distortions (3−4%). In the case of M(TPP)(Ph)₄(CH₃)₄·C₆₀ cocrystal, it showed mainly saddled (∼83%), minimal ruffled (8%) and domed (8%) distortions of the macrocyclic ring. In-plane displacement on the 24-atom core of the porphyrin in these cocrystallates features generally a varying degree of N-str (B_1g) and bre (A_1g) distortions.