Tapes, sheets, and prisms. Identification of the weak C-F interactions that steer fullerene-porphyrin cocrystallization

Tetra(pentafluorophenyl)porphyrin (H2TPFPP) has been cocrystallized with C60 from arene solvents to give H 2TPFPP·C60, 1, H2TPFPP·C 60·8Benzene, 3, and 3H2TPFPP·2C 60·6Toluene, 4. Their X-ray structures have been determined to identify the supramolecular interactions that lead to tape, sheet, and prismatic packing motifs. In addition to close fullerene-porphyrin π-π interactions, attractive C-F⋯H-C interactions are important in connecting the C6F5 groups of one porphyrin to the pyrrole positions of a neighbor. This interaction is also seen in the structure of the free-base porphyrin H2TPFPP·3p-Xylene, 2. © 2006 American Chemical Society

Noncovalent endo-binding of fullerenes to diprotonated bisporphyrins

Noncovalent binding of fullerenes to bisporphyrins was studied in the gas phase by energy-dependent collision-induced dissociation (CID) with Xe under single-collision conditions. The electrospray ionization mass spectra of calix[4] arene-linked bisporphyrins show that bisporphyrins take up to 3-4 protons, depending on the type of meso-substituents. Of the protonated bisporphyrins, the diprotonated species form stable 1:1 complexes with fullerenes (C-60 and C-70). CID cracking patterns of the diprotonated bisporphyrins indicate that each monomeric porphyrin moiety is singly protonated. CID yield-energy curves obtained from the 1:1 diprotonated bisporphyrin-fullerene complexes suggest that a fullerene occupies the endo-binding site intercalated between the two singly protonated porphyrin moieties. In the cases of 1:2 diprotonated bisporphyrin-fullerene complexes, CID results show that one fullerene binds inside (endo-binding) and the other outside (exo-binding). The exo-binding mode is energetically almost identical to the binding of fullerenes to singly protonated porphyrin monomers. The endo-binding energy is at least twice the exo-binding energy. To gain insights into the binding mode, we optimized structures of diprotonated bisporphyrins and their 1:1 endo-complexes with fullerenes, and calculated the endo-binding energy for C-60, C-70 (end-on), and C-70 (side-on). The endo-binding of fullerenes to diprotonated bisporphyrins nearly doubles the pi-pi interactions while reducing the electrostatic repulsion between the two singly protonated porphyrin moieties. The side-on binding of C-70 is favored over the end-on binding because the former exerts less steric strain to the lower rim of calixarene.open1155sciescopu