Single Crystals of a Highly Conductive Three-Dimensional Conjugated Coordination Polymer

Conjugated coordination polymers (CCPs), which possess long-range planar π-d conjugation, are fascinating for various applications because they inherit the merits of both metal-organic frameworks (MOFs) and conducting polymers. However, only one-dimensional (1D) and two-dimensional (2D) CCPs have been reported so far. The synthesis of three-dimensional (3D) CCPs is challenging and even seems theoretically infeasible because conjugation implies 1D or 2D structure. Besides, the redox activity of the conjugated ligands and the π-d conjugation makes the synthesis of CCPs very complicated, and hence, single crystals of CCPs are rarely achieved. Herein, we reported the first 3D CCP and its single crystals with atomically precise structures. The synthesis process involves complicated in situ dimerization, deprotonation of ligands, oxidation/reduction of both ligands and metal ions, and precise coordination between them. The crystals contain in-plane 1D π-d conjugated chains and close π-π interactions between the adjacent chains that are bridged by another column of stacked chains, thus forming 3D CCP with high conductivity (400 S m^-1 at room temperature and 3100 S m^-1 at 423 K) and potential applications as cathodes in sodium-ion batteries with high capacity, rate capability, and cyclability.