However, macrocycles such as cycloparaphenylenes (CPPs), 10 cucurbiturils and cyclodextrins 11 often adopt compact non-porous herringbone packing arrangements when they crystallize. In the whole family of the CPPs, only one member, [6]CPP, has been reported to crystallize in a porous tubular arrangement. In this case, the tubular stacks can be reinforced by intermolecular interactions; for example, CPPs form nanotube-like arrays after partial substitution with fluorine, due to intermolecular C-H⋯F interactions. This type of packing can be utilized as a confined space to form host-guest composites. Based on the six-fold symmetry of the porphyrin nanoring c-P6•T6 (Fig. ), it might be expected to form hexagonal arrays, resulting in tubular stacks and infinite 2D sheets due to the stacking between the planar walls oriented perpendicularly to the macrocycle. However, the only crystal structure reported previously for this nanoring complex, which we call here the P6-I polymorph, exhibits a herringbone-type packing (Fig. ). A curious feature of this structure is that the butadiyne linkers are substantially curved above and below the mean plane of the six zinc atoms (Fig. ). This distortion was attributed to the fact that the template is too small for the cavity of the nanoring (by ca. 2.5%), but, surprisingly, the gas-phase geometry of c-P6•T6, calculated using density functional theory (DFT), has a different structure, with the butadiyne-linkers in the plane of the zinc atoms. The difference between these two structures is seen from the overlay in Fig. . The nanoring seems to have two ways to contract around the template: (a) tilting planar porphyrins to the side, resulting in a ruffled perimeter, displacing of butadiyne linkers out of plane, as in P6-I, or (b) bending the porphyrin skeleton to move the Zn ion away from the porphyrin mean plane, as in the gas-phase structure. This difference can be seen more clearly by plotting the distance of the linking butadiyne carbon atoms from the mean plane of the zinc centers (clink, defined in Figure ) against the Zn to porphyrin plane distance, as shown in Fig. (gray circles for P6-I; cross for the gas-phase structure). The work presented here reveals that the gas-phase structure and P6-I are extreme cases, and that other polymorphs of c-P6•T6 exhibit combinations of both types of distortion, to give a spectrum of molecular geometries, as shown in Fig. .