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

Abstract

Due to their diverse potential in advanced electronics and energy technologies, electrically conducting metal-organic frameworks (MOFs) are drawing significant attention. Although hexagonal 2D MOFs generally display impressive electrical conductivity because of their dual in-plane (through bonds) and out-of-plane (through π-stacked ligands) charge transport pathways, notable differences between these two orthogonal conduction routes cause anisotropic conductivity and lower bulk conductivity. To address this issue, we have developed the first redox-complementary dual-ligand 2D MOF Cu₃(HHTP)(HHTQ), featuring a π-donor hexahydroxytriphenylene (HHTP) ligand and a π-acceptor hexahydroxytricycloquinazoline (HHTQ) ligand located at alternate corners of the hexagons, which form either parallel HHTP and HHTQ stacks (AA stacking) or alternating HHTP/HHTQ stacks (AB stacking) along the c-axis. Regardless of the stacking pattern, Cu₃(HHTP)(HHTQ) supports more effective out-of-plane conduction through either separate π-donor and π-acceptor stacks or alternating π-donor/acceptor stacks, while promoting in-plane conduction through the pushpull-like heteroleptic coordination network. As a result, Cu₃(HHTP)(HHTQ) exhibits higher bulk conductivity (0.12 S/m at 295 K) than single-ligand MOFs Cu₃(HHTP)₂ (7.3 × 10⁻² S/m) and Cu₃(HHTQ)₂ (5.9 × 10⁻⁴ S/m). This work introduces a new design approach to improve the bulk electrical conductivity of 2D MOFs by supporting charge transport in both in- and out-of-plane direcations.