Nickel(II) porphyrin/fullerene C70 porous molecular cocrystal featuring a robust one-dimensional channel

Abstract

Molecular cocrystals are crystalline materials composed of multiple types of molecular components held together by noncovalent interactions. Among these, porphyrin-fullerene cocrystals represent a well-studied class of supramolecular assemblies. The close packing arrangement between porphyrins and fullerenes is known to contribute to high crystallinity and structural stability. Porphyrin-fullerene cocrystal systems including C60, which has a spherical shape, have provided insights on intermolecular interaction. In contrast, cocrystals incorporating C₇₀, which has an ellipsoidal shape, remain relatively unexplored, and the influence of fullerene shape on cocrystal structures and stability remains unclear. In this study, we investigate the differences between C60 and C70 using cocrystals of a nickel(II) porphyrin derivative (NiTEPP) with these fullerenes. Two distinct cocrystals were successfully obtained: the porous cocrystal NiTEPP/C₇₀ featuring one-dimensional channels, and the nonporous crystal NiTEPP/C₇₀-n. High-pressure single-crystal X-ray diffraction results show that these cocrystals maintained their single crystal structure under high pressure. Furthermore, intermolecular interaction energies depending on the fullerene species were evaluated using density functional theory calculations. The combined experimental and theoretical results demonstrate that the shape of the fullerene plays a crucial role in governing intermolecular interactions and structural stability, and these results provide valuable guidelines for the rational design of molecular cocrystals with controlled intermolecular interactions.