Synthesis and Characterization of Three-Dimensional Electrically Conductive Metal-Organic Framework with Extended-Conjugation

Abstract

2D conductive metal-organic frameworks (MOFs), which exhibit high electrical conductivity, are promising candidates for diverse applications. However, the majority of reported 2D MOFs exhibit a stacking structure with a close interlayer distance, leaving room for improvement in achieving higher porosity and enhanced accessibility to open metal sites by widening the gap between the layers. In this study, we developed a 3D conductive MOF, Ni-HBC, with high electrical conductivity and porosity by utilizing nonplanar ligands and solvent interactions of Ni at axial positions, thereby forming 3D extended conjugation pathways in a non-interpenetrated structure. The non-interpenetrated porous crystal structure was verified using PXRD, HRTEM, and N2 adsorption isotherm analysis. Furthermore, XPS and XANES indicated the presence of a [NiO6] octahedral configuration. Electrical conductivity measurements with a two-probe method showed a conductivity of 1.61×10-4 S/cm, while variable- temperature conductivity measurements revealed an activation energy of 279 meV. Additionally, the thermoelectric properties of Ni-HBC exhibited a thermal conductivity of less than 0.2 W/mK and Seebeck coefficient of approximately 90 μV/K.