Vapor diffusion of methanol into solution of free-base ring c-P6-free in o-dichlorobenzene containing 2.0 equiv. of C60 provided P6-C60 as dark green blocks. Each nanoring is surrounded by six fullerenes (Fig. ) which stack to the porphyrin walls, forming continuous layers. The rings in the different layers are shifted with respect to each other (unlike in P6-II and P6-III). The most striking feature is the geometry of the nanoring itself: it is highly elliptical (major axis: 30.2 Å, minor axis: 20.2 Å; Fig. ), with two butadiyne bridges slightly bent (largest clink 0.18 Å) and the others in plane (Fig. ) with largest clink 0.02 Å), reflecting the surprising flexibility of the metal-free ring compressed in between fullerenes. On the contrary, GFN2-xtb 23 calculations for the free-base ring in the gas phase indicate that the lowest energy conformation is circular (Fig. ). The bending of the ring in the solid state to an elliptical conformation is evidently caused by interactions with fullerenes and other crystal-packing effects. The model shows short porphyrin centroid -fullerene 6:6 ring juncture contacts, as commonly observed for cocrystals with porphyrins, 24 with shortest contact of 2.772 (7) Å between the centroid of the 6:6 ring juncture and the centroid of the 24atom porphyrin plane (Fig. ). In contrast to the crystals of P6-II, P6-III and P6-IV, those of P6-C60 are difficult to re-dissolve, reflecting the strength of the crystal packing and interactions between fullerene molecules and the nanorings. There have been few reported cyclic fullerene receptors with three porphyrin walls surrounding fullerene molecules, 25 and none of them were characterized by single-crystal X-ray crystallography. The Cambridge Structural Database contains only a few examples of a fullerene molecule stacking to three porphyrins. Structure P6-C60 is highly porous and solvent-accessible voids constitute 40% of the unit cell volume (calculated with Mercury 4.0 software, 19 probe radius 1.2 Å, after removing refined solvent molecules). This structure features infinite channels running though the solvent-filled cavities of the nanorings, along the direction of the a axis, as shown in Figure . We analyzed these channels using with the software tool Zeo++ 28 which gave a largest free sphere diameter of 13.5 Å; this is the largest free sphere that can move unimpeded between the periodic repeats of the channel. The largest included sphere diameter is 16.8 Å (both calculated using a probe radius of 1.2 Å).