Electron-Deficient Porphyrin-Fullerene Cocrystallates: Effect of Fullerene on the Porphyrin Ring Conformation

A new family of electron-deficient porphyrin-fullerene cocrystallates were examined by single crystal X-RD. Solvated cocrystallates of 2,3,12,13-tetracyano-5,10,15,20-tetraphenylporphyrin, {[H₂(TPP)(CN)₄]₃•C₆₀, 1, [Cu(TPP)(CN)₄]₃•C₆₀, 2 and [H₂(TPP)(CN)₄]•C₇₀, 3} were examined to elucidate the influence of fullerene on the stereochemistry of the porphyrin macrocycle and the extent of intermolecular interactions in the solid-state. The C₆₀ units are encapsulated into the triporphyrin capsule and intermolecular interactions are dominated by mainly porphyrin…C₆₀ and porphyrin…porphyrin π…π type of interactions. Both the cocrystallates revealed the formation of hexagonal honeycomb layer-like structure with 10 Å cavity filled with lattice solvates. On changing the fullerene to C₇₀, co-crystallate, 3 showed essentially one-dimensional chain structure. Cocrystallates, 1-3 showed considerable distortion of the porphyrin ring as evidenced from root-mean square (r.m.s.) deviation which is the deviation of the 24-atoms of the macrocycle from their least square plane (0.25 Å) relative to that observed in nearly planar (0.046 Å) parent free base porphyrin, H₂(TPP)(CN)₄ structure. Another less electron rich porphyrin-fullerene cocrystallate, H₂(TPP)Br₄•(C₆₀)₂•(TCE)₂, 4 revealed corrugated layer-structure mediated by solvent and porphyrin…C₆₀ interactions. The macrocycle in the cocrystallate, 4 shows slightly higher distortion than that observed in the reported structure, H₂(TPP)Br₄. In these cocrystallates, the intermolecular close contact distances between the porphyrin…fullerene was found to be (por)C…C(C₆₀) = 3.185(16) Å and (C₇₀)C…N(por) = 3.03 (3) Å. The normal coordinate structure decomposition analysis of the macrocycle for out-of-plane distortion in the cocrystallates, 1-3 revealed considerable saddling (69-71%) with very minimal ruffled (2-8%) and domed (10-15%) distortions. Cocrystallate, 4 shows enhanced of wave distortion than that observed in the parent porphyrin, H₂(TPP)Br₄. The nonplanar distortion of the porphyrin ring in the cocrystallates has been ascribed mainly to intermolecular interactions.