Porphyrins and fullerenes are spontaneously attracted to each other. This new supramolecular recognition element can be used to construct discrete host-guest complexes, as well as ordered arrays of interleaved porphyrins and fullerenes. The fullerene-porphyrin interaction underlies successful chromatographic separations of fullerenes, and there are promising applications in the areas of porous framework solids and photovoltaic devices.

Porphyrins and fullerenes are spontaneously attracted to each other. This supramolecular recognition element can be exploited to produce ordered arrays of interleaved porphyrins and fullerenes. C(60) x H(2)TpyP x Pb(NO(3))(2) x 1.5TCE (H(2)TpyP = tetra-4-pyridylporphyrin; TCE = 1,1,2,2-tetrachloroethane) crystallizes in the tetragonal P4/n space group and the structure has been solved to high resolution. The Pb(2+) ions connect the pyridylporphyrins in infinite sheets with an interlayer spacing of 12.1 A. The fullerenes are intercalated between these layers, acting as pillars. The 6:6 ring juncture bonds of C(60) are centered over the porphyrins, bringing the layers into strict tetragonal register. This arrangement identifies the fullerene-porphyrin interaction as a structure-defining element. The same motif is seen in a related ribbon structure having C(70) intercalated into HgI(2)-linked H(2)TpyTP. The supramolecular design principles involved in assembling these chromophores may have applications in materials science.

The boron subphthalocyanine cation, B(SubPc)+, has been prepared as a salt of a weakly coordinating carborane anion, CHB11Me 5Br6-, by a metathesis reaction of Et 3Si(CHB11Me5Br6) with B(SubPc)Cl. The separation of the cation and anion in the X-ray structure indicates coordinative unsaturation at the boron center, and this is corroborated by DFT calculations. A strongly Lewis acidic nature for the B(SubPc)+ cation is indicated by its hydrolysis to an unusual product, the di-meso-N-protonated -oxo dimer, [H(SubPc)B-O-B(SubPc)H]2+. ©2006 Wiley Periodicals, Inc.

Electron spin transient nutation (ESTN) experiments show that the spin multiplicity of the ground state of C603- in frozen solution is a doublet with S = 1/2. In purified samples, there is no evidence for excited states or other species with higher multiplicity. In the anions of C120On- (n = 2, 3, 4), where the CW EPR experiments have shown that a mixture of species is present, ESTN experiments confirm that a doublet with S = 1/2 is associated with the 3- anion and triplets with S = 1 are associated with the 2- and 4- anions. A weak nutation peak attributable to ms = -1/2 ↔ 1/2 transitions within a quartet state may arise from association of anions with spins of 1/2 and 1 in solute aggregates.

A calix[4]arene scaffolding has been used to construct bisporphyrin ("jaws" porphyrin) hosts for supramolecular binding of fullerene guests. Fullerene affinities were optimized by varying the nature of the covalent linkage of the porphyrins to the calixarenes. Binding constants for C60 and C70 in toluene were explored as a function of substituents at the periphery of the porphyrin, and 3,5-di-tert-butylphenyl groups gave rise to the highest fullerene affinities (26,000 M(-1) for C60). The origin of this high fullerene affinity has been traced to differential solvation effects rather than to electronic effects. Studies of binding constants as a function of solvent (toluene < benzonitrile < dichloromethane < cyclohexane) correlate inversely with fullerene solubility, indicating that desolvation of the fullerene is a major factor determining the magnitude of binding constants. The energetics of fullerene binding have been determined in terms of DelatH and DeltaS and are consistent with an enthalpy-driven, solvation-dependent process. A direct relationship between supramolecular binding of a fullerene guest to a bisporphyrin host and the appearance of a broad NIR absorption band have been established. The energy of this band moves in a predictable manner as a function of the electronic structure of the porphyrin, thereby establishing its origin in porphyrin-to-fullerene charge transfer.

We present a novel nuclear magnetic resonance experiment for establishing through-bond connectivity in solids using scalar coupling-driven correlation. This method, a variant of the popular double-quantum-filtered correlation spectroscopy experiment in liquids, is robust under fast magic-angle-spinning conditions and in the presence of dynamics. In HC(60)(+), where anisotropic molecular motion renders through-space dipolar-driven correlation ineffective, this through-bond correlation method answers a significant structural question by accurately identifying the direct bond between the protonated sp(3) hybridized carbon site and the sp(2) hybridized cationic site.

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.

Porphyrins and fullerenes are spontaneously attracted to each other. This new supramolecular recognition element is explored in discrete, soluble, coordinatively linked porphyrin and metalloporphyrin dimers. Jawlike clefts in these bis-porphyrins are effective hosts for fullerene guests. X-ray structures of the Cu complex with C60 and free-base complexes with C70 and a pyrrolidine-derivatized C60 have been obtained. The electron-rich 6:6 ring-juncture bonds of C60 show unusually close approach to the porphyrin or metalloporphyrin plane. Binding constants in toluene solution increase in the order Fe(II) < Pd(II) < Zn(II) < Mn(II) < Co(II) < Cu(II) < 2H and span the range 490-5200 M-1. Unexpectedly, the free-base porphyrin binds C60 more strongly than the metalated porphyrins. This is ascribed to electrostatic forces, enhancing the largely van der Waals forces of the pi-pi interaction. The ordering with metals is ascribed to a subtle interplay of solvation and weak interaction forces. Conflicting opinions on the relative importance of van der Waals forces, charge transfer, electrostatic attraction, and coordinate bonding are addressed. The supramolecular design principles arising from these studies have potential applications in the preparation of photophysical devices, molecular magnets, molecular conductors, and porous metal-organic frameworks.

Aspects of the electron paramagnetic resonance (EPR) spectra of C60n- fulleride ions (n = 2, 3) and the EPR signal observed in solid C60 are reinterpreted. Insufficient levels of reduction and the unrecognized presence of C120O, a ubiquitous and unavoidable impurity in air-exposed C60, have compromised most previously reported spectra of fullerides. Central narrow line width signals ("spikes") are ascribed to C120On- (n = odd). Signals arising from axial triplets (g approximately 2.0015, D = 26-29 G) in the spectrum of C602- are ascribed to C120On- (n = 2 or 4). Their D values are more realistic for C120O than C60. Less distinct signals from "powder" triplets (D approximately 11 G) are ascribed to aggregates of C120On- (n = odd) arising from freezing nonglassing solvents. In highly purified samples of C60, we find no evidence for a broad approximately 30 G signal previously assigned to a thermally accessible triplet of C60(2-). The C60(2-) ion is EPR-silent. Signals previously ascribed to a quartet state of the C60(3-) ion are ascribed to C120O4-. Uncomplicated, authentic spectra of C60- and C60(3-) become available when fully reduced samples are prepared under strictly anaerobic conditions from freshly HPLC-purified C60. Solid off-the-shelf C60 has an EPR signal (g approximately 2.0025, DeltaH(pp) approximately 1.5 G) that is commonly ascribed to the radical cation C60*+. This signal can be reproduced by exposing highly purified, EPR-silent C60 to oxygen in the dark. Doping C60 with an authentic C60*+ salt gives a signal with much greater line width (DeltaH(pp) = 6-8 G). It is suggested that the EPR signal in air-exposed samples of C60 arises from a peroxide-bridged diradical, *C60-O-O-C60* or its decomposition products rather than from C60*+. Solid-state C60 is more sensitive to oxygen than previously appreciated such that contamination with C120O is almost impossible to avoid.