Supramolecular Organization of C60 into Linear Columns of Five-Fold

When cocrystallized with calix[5]arene, C60 arranges to form linear, five-fold, Z-shaped columns consisting of molecular spheres that are in van der W...
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CRYSTAL GROWTH & DESIGN 2002 VOL. 2, NO. 1 3-6

Articles Supramolecular Organization of C60 into Linear Columns of Five-Fold, Z-Shaped Strands Jerry L. Atwood,*,† Leonard J. Barbour,*,† and Colin L. Raston*,‡ Department of Chemistry, University of MissourisColumbia, Columbia, Missouri 65211 and School of Chemistry, University of Leeds, Leeds LS2 9JT, United Kingdom Received September 4, 2001

W This paper contains enhanced objects available on the Internet at http://pubs.acs.org/crystal. ABSTRACT: When cocrystallized with calix[5]arene, C60 arranges to form linear, 5-fold, Z-shaped columns consisting of molecular spheres that are in van der Waals contact with one another. The fullerene molecules are present in three completely different environments with regard to their supramolecular association with the calixarene molecules. Arguably, few compounds have rivaled the fullerenes in capturing the collective imagination of the scientific community. They have been targeted as molecular building blocks with a view to producing new materials with novel functions. In this regard, we1 and others2 have been studying supramolecular complexes of both C60 and C70 in the solid state to gain some understanding of how these molecules can be induced to pack in very different and, most particularly, highly organized arrays. As early as 1993, Rao et al. demonstrated that solid films of face-centered cubic (fcc) C60 can be polymerized photochemically by cross-linking neighboring molecules in van der Waals contact with one another via a [2 + 2] cycloaddition reaction.3 Owing to the three-dimensional arrangement of the C60 molecules, there was no control over the dimensionality of the linkages, and the polymer was therefore highly branched. A significant advance was made when Iwasa et al. were able to effect a highyield synthesis of the dumb-bell-shaped C60 dimer, C120.4 These researchers subjected crystals of a complex of C60 with ET [ET ) bis(ethylenedithio)tetrathiafulvalene], (ET)2C60,5 to a pressure of 5 GPa at 200 °C. The ET molecules envelope a one-dimensional arrangement consisting of a double column of staggered C60 molecules, with the latter situated at center-to-center distances of 9.923 and 9.919 Å from one another (cf. 10.02 Å in pristine fcc C60). It is also noteworthy that this approach produced C120 dimers in ca. 80% yield, whereas a previously reported mechanochemical method6 yielded only 20-30% of the product from pure fcc C60. The ability to form the dimer in high yield represents a * To whom correspondence should be addressed. E-mail: atwoodj@ missouri.edu, [email protected], [email protected]. † University of MissourisColumbia. ‡ University of Leeds.

striking example of how the principles of supramolecular chemistry can be employed to prearrange molecules for controlled covalent chemistry. As part of our ongoing studies in this area, we recently reported the structure of a cocrystalline complex of C60 with p-bromocalix[4]arene propyl ether in which the fullerene molecules assemble into one-dimensional, but well-separated, columns of closely spaced [9.8782(5) Å] spheres.1c Subsequently, using the method outlined by Iwasa,4 Sun and Reed were able to exploit this preorganized structure to engineer linear polymers of (C60)n.7 We now report a solid-state structure in which C60 molecules are arranged in discrete, linear columns of Z-shaped 5-fold strands and which has implications for preparing multistrand higher order polymers.

In addition to preorganization by cocrystallization, we have long since been interested in the supramolecular encapsulation of fullerenes as a “ball-and-dual-socket” nanostructure.8 To this end, we prepared the cocrystalline complex of C60 with calix[5]arene, 1. The latter is a relatively large and rigid bowl-shaped molecule, and we anticipated a structure in which two molecules of 1 would encapsulate a single molecule of C60 in a manner akin to that previously observed for two related calixarenes.9

10.1021/cg0155494 CCC: $22.00 © 2002 American Chemical Society Published on Web 11/27/2001

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Figure 1. (a) The asymmetric unit consisting of five C60, four calix[5]arene, and two toluene molecules. The C60 guest molecules are colored according to their modes of interaction with the calix[5]arene host cavities (green: ball-and-dual-socket, red: balland-socket,8b blue: not interacting). (b) Cut away section (bottom) of the space filling metaphor for ball-and-dual-socket nanostructure (top) showing the complementarity of curvature of the fullerene with the calixarene. W A 3D rotatable image of panel a in xyz format is available.

Figure 2. The extended structure viewed along [100] (red: calix[5]arene; blue: C60; green: toluene). (a) The direction of the projection is parallel to the 5-fold, Z-shaped columns of C60. (b) The C60 molecules have been removed to show the infinite channels running along [100].

Crystals suitable for X-ray diffraction analysis10 were grown by slow evaporation of a 1:1 mixture of 1 and C60 in toluene, and the structure was solved only with much difficulty. While the unit cell parameters and Laue symmetry of the diffraction record both indicated that the crystal system might be orthorhombic, the correct system was eventually determined to be pseudoorthorhombic, but monoclinic. As an added complication, the crystals were twinned, and employment of a suitable twinning law was required during refinement. The asymmetric unit is shown in Figure 1 and consists of 474 non-hydrogen atoms: five C60, four calix[5]arene, and two toluene molecules. Although most of the asymmetric unit appears to straddle a noncrystallographic mirror plane, one calix[5]arene and both solvent molecules are positioned such that their orientations are inconsistent with such a symmetry element.

Remarkably, the five crystallographically unique C60 molecules are present in all three possible environments. One of them is encapsulated by two calix[5]arene molecules which is the structural arrangement we had anticipated, while another two are each only associated with the bowl-shaped cavity of a single calixarene. The remaining two C60 molecules, as well as the two toluene solvent molecules, are situated in the lattice and do not interact with any of the calixarene cavities. Owing to the extraordinary complementarity of curvature of the fullerene with the cavity of the calixarene (Figure 1), all four of the unique calix[5]arene molecules are positioned such that their cavities are in van der Waals contact with fullerene molecules. With all due deference to the unpredictability of crystal structures, the overall arrangement of the molecules comprising the asymmetric unit seemed to

Supramolecular Organization of C60

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Figure 3. Space-filling projections of a single 5-fold strand of C60 together with its envelope of calixarene and toluene molecules viewed along (a) [100], (b) [01 h 0], and (c) [001]. The molecular color scheme is identical to that used in Figure 2. The origin is at top left for a and b, and at bottom left for c.

Figure 4. Space-filling projections showing a portion of a single 5-fold strand of C60 molecules (a) in a 3/4 view along the column and (b) from the side. The C60 molecules are colored according to their mode of interaction with the calixarene cavities as shown in Figure 2.

us at first to be overly complex, especially given that the asymmetric unit of each of the two previously known structures9 of substituted calix[5]arenes with C60 consisted only of one complete calixarene and one-half of a C60 molecule. In both of these cases, the extended structure was simply a manifestation of the threedimensional packing arrangement of the (calixarene)2‚ C60 ball-and-dual-socket nanostructure. Presumably, in those structures the steric hindrance of the substituents in the p-positions of the calixarenes and the absence of less shrouded fullerenes precludes any fullerenefullerene interactions, unlike in the present structure for the same nanostructure (see below). Indeed, the complexity of the present structure can best be understood by considering the extended structure (see Figures 2-4). Figure 2 shows clearly that the C60 molecules arrange to form 5-fold linear columns along the crystallographic a axis. The cross-section of these columns is approximately Z-shaped, and the calix[5]arene and toluene molecules serve to separate the 5-fold fullerene strands from one another. The projections provided in Figure 3b and c show that the C60-containing channels are not interlinked, thereby illustrating that the one-dimensional, 5-fold, Z-shaped

fullerene strands are discrete (i.e., the fullerene molecules in one channel are not in close van der Waals proximity to fullerenes in a neighboring channel.) The fascinating arrangement of the C60 strand is shown in Figure 4. The central column consists entirely of C60 molecules that are interacting with calixarenes via the ball-and-socket mode. The two neighboring columns consist purely of noninteracting (i.e., with respect to the calixarene cavities) fullerenes and the columns at the two extremities consist of fullerenes associated with alternating ball-and-socket and balland-dual-socket nanostructures. Within the 5-fold strand, neighboring columns of C60 molecules are offset with respect to one another in order to facilitate close packing of the spheres. Figure 5 shows that the structure contains 14 unique nearest-neighbor C60 center‚‚‚center contacts. Owing to their somewhat different immediate environments, the C60 molecules in the 5-fold strand are situated at distances from one another that range from 9.880 to 10.720 Å. These distances are comparable to those expected for van der Waals interactions. In summary, we have established a structure with a remarkably complex and unprecedented arrangement of C60 molecules. It is noteworthy that the cavitand,

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(2)

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Figure 5. Projection showing all the unique C60‚‚‚C60 nearestneighbor contacts within the 5-fold strand. The fullerene center‚‚‚center distances (in Å) are A ) 10.431, B ) 10.275, C ) 10.345, D ) 10.367, E ) 10.720, F ) 10.001, G ) 9.976, H ) 10.049, I ) 9.961, J ) 10.161, K ) 10.205, L ) 10.627, M ) 10.082, N ) 9.880.

cyclotriveratrylene, CTV, with a shallower rigid bowl, forms two complexes (CTV)(C60)n, n ) 111 or 1.5,8b,12 depending on the concentration of the CTV relative to the fullerene. In contrast, in the present study it appears that only one complex results. Its complexity, coupled with the versatility of CTV in forming different complexes with C60, and the complexity of the CTV structure for n ) 1.5, suggests that other more complex structures are accessible, perhaps even using mixed rigid cavitand systems (the CTV structure with n ) 1.5 contains two-dimensional sheets of fullerenes separated by CTV molecules with two-thirds of the fullerenes present as part of ball-and-socket nanostructures, the other not associated with a CTV (cf. one of the fullerenes in the present structure,11 whereas the n ) 1 structure is comprised of single linear strands of C60 with each C60 part of a ball-and-socket nanostructure.)

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Acknowledgment. This work was supported by the National Science Foundation and the Australian Research Council. We thank Dr. Michael Ruf of Bruker AXS for data collection and advice regarding the twinning of the structure. Supporting Information Available: X-ray crystallographic information file (CIF) for structural studies. This information is available free of charge via the Internet at http:// pubs.acs.org.

References (1) (a) Barbour, L. J.; Orr, G. W.; Atwood, J. L. Chem. Commun. 1997, 1439-1440. (b) Rose, K. N.; Barbour, L. J.; Orr, G. W.; Atwood, J. L. Chem. Commun. 1998, 407-408. (c) Barbour, L. J.; Orr, G. W.; Atwood, J. L. Chem. Commun. 1998, 1901-1902. (d) Grey, I. E.; Hardie, M. J.; Ness, T. J.; Raston, C. L. Chem. Commun. 1999, 1139-1140. (e) Croucher, P. D.; Nichols, P. J.; Raston, C. L. J. Chem. Soc., Dalton Trans. 1999, 279-284. (f) Croucher, P. D.; Marshall, J. M. E.; Nichols, P. J.; Raston, C. L. Chem. Commun. 1999, 193194. (g) Andrews, P. C.; Atwood, J. L.; Barbour, L. J.; Croucher, P. D.; Nichols, P. J.; Smith, N. O.; Skelton, B.

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W.; White, A. H.; Raston, C. L. J. Chem. Soc., Dalton Trans. 1999, 2927-2932. (h) Andrews, P. C.; Atwood, J. L.; Barbour, L. J.; Nichols, P. J.; Raston, C. L. Chem. Eur. J. 1998, 4, 1384-1387. (a) Izuoka, A.; Tachikawa, T.; Sugawara, T.; Suzuki, Y.; Konno, M.; Saito, Y.; Shinohara, H. J. Chem. Soc., Chem. Commun. 1992, 1472-1473. (b) Crane, J. D.; Hitchcock, P. B.; Kroto, H. W.; Taylor, R.; Walton, D. R. M. J. Chem. Soc., Chem. Commun. 1992, 1764-1765. (c) Eichhorn, D. M.; Yang, S.; Jarrell, W.; Baumann, T. F.; Beall, L. S.; White, A. J. P.; Williams, D. J.; Barrett, A. G. M.; Hoffman, B. M. J. Chem. Soc., Chem. Commun. 1995, 1703-1704. (d) Veen, E. M.; Postma, P. M.; Jonkman, H. T.; Spek, A. L.; Feringa, B. L. Chem. Commun. 1999, 1709-1710. (e) Narymbetov, B.; Kobayashi, H.; Tokumoto, M.; Omerzu, A.; Mihailovic, D. Chem. Commun. 1999, 1511-1512. Rao, A. M.; Zhou, P.; Wang, K.-A.; Hager, G. T.; Holden, J. M.; Wang, Y.; Lee, W.-T.; Bi, X.-X.; Eklund, P. C.; Cornett, D. S.; Duncan, M. A.; Amser, I. J. Science 1993, 259, 955957. Iwasa, Y.; Tanoue, K.; Mitani, T.; Izuoka, A.; Sugawara, T.; Yagi, T. Chem. Commun. 1998, 1411-1412. Izuoka, A.; Tachikawa, T.; Sugawara, T.; Suzuki, Y.; Konno, M.; Saito, Y.; Shinohara, H. J. Chem. Soc., Chem. Commun. 1992, 1472-1473. Wang, G.-W.; Komatsu, K.; Murata, Y.; Shiro, M. Nature 1997, 387, 583-586. Sun, D.; Reed, C. A. Chem. Commun. 2000, 2391-2392. (a) Atwood, J. L.; Koutsantonis, G. A.; Raston, C. L. Nature 1994, 368, 229-231. (b) Steed, J. W.; Junk, P. C.; Atwood, J. L.; Barnes, M. J.; Raston, C. L.; Burkhalter, R. S. J. Am. Chem. Soc. 1994, 116, 10346-10347. (c) Raston, C. L.; Atwood, J. L.; Nichols, P. J.; Sudria, I. B. N. Chem. Commun. 1996, 2615-2616. (d) Andrews, P. C.; Hardie, M. J.; Raston, C. L. Coord. Chem. Rev. 1999, 189, 169-198. (e) Atwood, J. L.; Barbour, L. J.; Raston, C. L.; Sudria, I. B. N. Angew. Chem., Int. Ed. Engl. 1998, 37, 981-983. (f) Hardie, M. J.; Raston, C. L. Chem. Commun. 1999, 11531163. (g) Hardie, M. J.; Godfrey, P. D.; Raston, C. L. Chem. Eur. J. 1999, 5, 1828-1833. (a) Atwood, J. L.; Barbour, L. J.; Nichols, P. J.; Raston, C. L.; Sandoval, C. A. Chem. Eur. J. 1999, 5, 990-996. (b) Haino, T.; Yanase, M.; Fukazawa, Y. Angew. Chem., Int. Ed. Engl. 1997, 36, 259-260. Crystal data for (calix[5]arene)4‚(C60)5‚(toluene)2: molecular formula: C454H136O20, monoclinic, space group P21/c, a ) 20.7389(17), b ) 37.858(3), c ) 31.463(3) Å, β ) 90.038(2)°, V ) 24703(4) Å3, Z ) 4, µ (Cu-KR) ) 0.761 mm-1, λ ) 1.54178 Å, 2θmax ) 49.5°, Dc ) 1.589 g cm-3. A dark red crystal of dimensions 0.30 × 0.25 × 0.20 mm3 was used. Intensity data (81 378 reflections, 24 275 unique) were collected at 173 K on a Siemens SMART 6000 CCD diffractometer using the omega scan mode. Data were corrected for absorption using the program SADABS. The structure was solved by direct methods (SHELXS-97), expanded by difference synthesis and refined by the full-matrix least-squares method on F2 (SHELXL-97). All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed in calculated positions with their thermal parameters fixed at values of 1.2 (1.5 for methyl hydrogen atoms) those of their parent atoms. Neighboring (bonded) carbon atoms were restrained to have the same Uij components. Such treatment is considered appropriate for large structures that are poorly resolved. Final refinement converged with R1 ) 0.2086 for 22873 unique reflections (I > 2σ(I), 2θmax ) 49.5°). Note: the rather high value for R1 is symptomatic of several inherent difficulties: the structure is pseudo-merohedrally twinned; the asymmetric unit is relatively large for a “small molecule” structure; although the C60 molecules are probably rotationally disordered, they were refined as rigid, nondisordered groups with fixed orientations. Atwood, J. L.; Barnes, M. J.; Gardiner, M. G.; Raston, C. L. Chem. Commun. 1996, 1449-1450. Bond, A. M.; Miao, W. J.; Raston, C. L.; Ness, T. J.; Barnes, M. J.; Atwood, J. L. J. Phys. Chem. B 2001, 105, 1687-1695.

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