Flexibility Induced by Four Heptagons: A Negatively Curved Polycyclic Aromatic Hydrocarbon Cut-Out of Schwarzite P216

A key feature of the, so far only theoretically described, family of sp² carbon allotropes called schwarzites is the negatively curved topology, which is introduced by the incorporation of heptagonal (or octagonal) rings in a graphene-type lattice. We have constructed a cut-out of this material with a unique pattern of four heptagonal rings arranged in a row by Pd-catalyzed [4 + 3] and [5 + 2] annulation and characterized it thoroughly. The pronounced flexibility of the π-system, which was investigated by temperature-dependent NMR as well as theoretical calculations, promises to be advantageous for a template-mediated synthesis approach toward the parent schwarzite P216, as it allows maximization of shape complementarity with rigid templates like fullerenes and orientational flexibility for subsequent C-C bond formations. We were able to prove and investigate the presence of supramolecular complexes with C₆₀ and C₇₀ in solution by concentration-dependent NMR titration experiments, as well as in the solid state by single-crystal X-ray and electron diffraction.