Hierarchical Self-Assembly of Curved Aromatics: From Donor-Acceptor Porphyrins to Triply Periodic Minimal Surfaces

A saddle-shaped pi-extended zinc porphyrin containing a peripheral pyridyl ligand undergoes quantitative self-assembly into a cyclic trimer. The trimer has a prismatic structure with negatively curved side walls, which promote the formation of supramolecular organic frameworks stabilized by dispersion interactions. The first framework type, UWr-1, has the npo topology, with a hexagonal structure analogous to the Schwartz H triply periodic minimal surface. Co-crystallization of the trimer with either C60 and C70 produces the isomorphous cubic UWr-2 and UWr-3 phases, characterized by the ctn network topology and a structural relationship to the Fischer-Koch minimal surface S. All three phases contain complex labyrinths of solvent-filled channels, corresponding to very large probe-accessible volumes (68 % to 76 %). The UWr-2 network could be partly desolvated while retaining its long range dimensional order, indicating remarkable strength of the dispersion interactions in the crystal. A theoretical analysis of noncovalent interactions shows the role of geometrical matching between the negatively curved porphyrin units and positively curved fullerenes. Hierarchical self-assembly of curved metalloporphyrin tectons via a combination of coordinative and non-covalent interactions leads to unprecedented supramolecular solids with extremely large void volumes. The intricate interaction patterns found in these solids are analogous to those in some metal- and covalent-organic frameworks, offering new routes toward porous molecular crystals.image