Modulating the Electronic Properties of Conductive Conjugated Coordination Polymers with Atomic-Level Precision

Abstract

Conductive metal–organic frameworks and conjugated coordination polymers (CCPs) are promising platforms for low-power electronics and sustainable energy technologies, yet charge-transport design rules remain elusive. In diamine-based frameworks, Cu-coordinated motifs exhibit electrical conductivities several orders of magnitude lower than those of their Ni analogs, but the origin of this disparity has remained unclear, complicating rational selection of earth-abundant metal nodes for multifunctional materials. Here, we report the synthesis and atomic-resolution characterization of Cu-TABQ, a diamine-based CCP grown as single-crystals from tetraamino-p-benzoquinone and copper ions. Microcrystal electron diffraction reveals a distorted pseudosquare-planar Cu-coordination with asymmetric imine bonding, electron localization, and a structural model consistent with possible local protonation/hydrogen bonding. In contrast, Ni-TABQ adopts a planar, symmetric coordination environment that supports charge delocalization and near-metallic transport. Density functional theory suggests that protonation stabilizes the distorted Cu-TABQ structure and suppresses charge transport. Together, these results support an atomic-level explanation for metal-dependent transport in diamine-based frameworks and establish the metal–ligand coordination environment and protonation as tunable handles for designing conductive frameworks.