An Electrically Conducting, Redox-Complementary Dual-Ligand 2D Graphitic MOF with Orthogonal Charge Transport Pathways

Owing to their diverse potential applications in modern electronics and energy technologies, electrically conducting metal–organic frameworks (MOFs) have emerged as one of the most coveted functional materials of the twenty-first century. Although 2D hexagonal MOFs often display impressive electrical conductivity due to their dual in-plane (through bonds) and out-of-plane (through π-stacked ligands) charge transport capabilities, large disparities between these two orthogonal conduction pathways cause anisotropic conductivity and dampen bulk conductivity. To address this issue, herein, we have developed the first redox-complementary dual-ligand 2D MOF (CDL-MOF1) Cu3(HHTP)(HHTQ) composed of a π-donor hexahydroxytriphenylene (HHTP) ligand and a π-acceptor hexahydroxytricycloquinazoline (HHTQ) ligand, which are heteroleptically coordinated to Cu(II) nodes and located at alternate corners of the hexagons, forming either parallel HHTP and HHTQ stacks (AA stacking) or alternating HHTP/HHTQ stacks (AB stacking) along the c-axis. Thus, irrespective of its stacking pattern, Cu3(HHTP) (HHTQ) can better facilitate out-of-plane conduction either through separate parallel π-donor and acceptor stacks or through alternating π-donor/acceptor stacks, while promoting in-plane conduction through push–pull-type heteroleptic coordination network. Consequently, CDL-MOF1 displayed higher bulk conductivity (0.12 S/m, 295 K) than its parent single-ligand MOFs Cu3(HHTP)2 (7.3 x 10^–2 S/m) and Cu3(HHTQ)2 (5.9 x 10^–4 S/m). This work presents a novel design strategy to improve the bulk electrical conductivity of 2D MOFs by facilitating both in- and out-of-plane charge transport.