Structure and Electrical Transport Properties of Metal Cate-Cholate Frameworks: The Metal Center Matters

Abstract

Two-dimensional conductive metal–organic frameworks (2D c-MOFs), constructed by coordination between metal ions and π-conjugated ligands, represent a unique class of materials that combine intrinsic porosity and electrical conductivity. However, the contribution of metal nodes to the overall electrical properties remains unclear. In this work, we systematically investigate the role of metal centers on a series of six highly crystalline hexahydroxytriphenylene (HHTP) based c-MOFs, M-HHTP, which incorporate alkaline earth including magnesium and calcium, as well as transition metals including cobalt, nickel, copper, and zinc. Comprehensive structural characterizations reveal that while all M-HHTP frameworks adopt a general honeycomb lattice, however, subtle variations in stacking patterns and coordination environments are induced by different metal ions. Electrical measurements show a pronounced dependence of conductivity on the nature of the metal nodes, in which the conductivity differs by four orders of magnitude due to the difference in metal centers. Furthermore, non-contact terahertz spectroscopy combined with theoretical calculations suggests that in alkaline earth metal-based MOFs, charge transport may proceed via a through-space hopping mechanism between organic ligands. This study elucidates the critical role of metal centers in governing charge transport in M-HHTP MOFs and offers valuable guidance for the rational design of high-performance 2D conductive frameworks.

Keywords

Conductive metal-organic frameworks / Metal catecholate compound / Electrical transport / Structure-property relationship / Coordination modes / Electronic structure / Coordination structures

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