Uninterrupted π-d Conjugated Three-Dimensional Conductive Metal-Organic Framework

Abstract

pi-d conjugation between metal ions and ligands facilitates long-range charge delocalization, enabling high electrical conductivity in two-dimensional conductive metal-organic frameworks (MOFs). However, understanding the intrinsic properties of pi-d conjugation is often hindered by coexisting pi-pi interactions. To address this, a three-dimensional (3D) conductive MOF, Ni3HBC (HBC = 2,3,6,7,10,11,14,15,18,19,22,23-dodecahydroxy-cata-hexabenzocoronene), was synthesized with a non-interpenetrated structure that suppresses pi-pi interactions while preserving pi-d conjugation as a primary charge transport pathway. Ni2+ ions coordinate with nonplanar ligands at equatorial positions and solvents at axial positions, resulting in a MOF with a surface area of 835 m2 g-1, an optical bandgap of 0.64 eV, and a room-temperature electrical conductivity of 1.98 x 10-4 S cm-1. Spectroscopic and magnetic analyses reveal the presence of semiquinone-based radicals and their ferromagnetic interaction with Ni2+ ions, providing a unique platform for studying pi-d conjugation and offering new insights into the design of 3D conductive MOFs.