Dedicated to Emeritus Professor Soichi Misumi on the occasion of his 77th birthday
Recently, a variety of layered carbon networks with closed, curved structures, such as carbon nanotubes, [1] bucky onions, [2] and "fullerene peapods" [3] have been discovered and have attracted much attention. Although the nature of the concave-convex interactions between the curved graphene sheets should be important in the formation and properties of these materials, they are yet to be well understood because of the absence of good model compounds. There have been considerable efforts towards the synthesis of belt-shaped conjugated systems. [4,5] In the accompanying paper, [6] we reported that the carbon nanorings [6]-and [8]paraphenyleneacetylene (1 and 2) have cavities with diameters of 13.2 and 17.3 , respectively (average values determined by X-ray diffraction), and form rather weak inclusion complexes with hexamethylbenzene and toluene, respectively. The size of the cavity in 1 appears to be suitable for the inclusion of C 60 (7.1 in diameter), although it is actually slightly too small when the depth of p orbitals (3.4 for benzene) is considered (Figure 1). Therefore, the host-guest chemistry of 1 with fullerenes would give an insight into the concave-convex p-p interactions that are associated with the bucky onion and fullerene peapod. Here, we report on the formation of unusually stable complexes of the carbon nanoring 1 with C 60 and bis(ethoxycarbonyl)methanofullerene (3), [7] and Xray crystallographic analysis of the crystalline 1:1 complex 1โข3.
Despite being only sparingly soluble in CHCl 3 , [8] C 60 was found to be much more soluble (approximately 5 mg per mL) in the presence of 1, to give the 1:1 complex 1โขC 60 as a reddish brown solution, or a dark red-brown solid which precipitated out at higher concentrations. The solid complex could be redissolved completely in CHCl 3 , which is in sharp contrast to the behavior of the solid calix[8]arene-C 60 complex, [9,10] where C 60 remained undissolved when added to CHCl 3 ; [