Proton Conductive Supramolecular Architectures Based on a Cobalt Terpyridine–Biimidazole Complex: Hydrogen‐Bonded Hexamer and Mixed‐Valence 1D Chain

Despite extensive research on hydrogen‐bonded frameworks, cobalt‐based coordination complexes with biimidazole ligands remain largely unexplored, and their potential as proton‐conducting materials has not been comprehensively investigated. Therefore, this paper reports the synthesis, crystal structures, and proton conduction properties of novel hydrogen‐bonded cobalt(II/III) coordination complexes incorporating 2,2′‐biimidazole (H 2 bim) and 4′‐carboxyl‐2,2′:6′,2″‐terpyridine (COOH‐terpy) ligands. Two supramolecular architectures were obtained via ligand exchange reactions in methanol: a hydrogen‐bonded hexamer, {Co III (COO‐terpy)(H 2 bim)(SCN)} 6 ([ 1 ] 6 ), and a mixed‐valence 1D hydrogen‐bonded chain, {[Co II (COO‐terpy)(H 2 bim)(NCS)][Co III (COO‐terpy)(H 2 bim)(SCN)]} n ([ 2 ] n ). Single‐crystal X‐ray diffraction revealed that both structures feature extensive hydrogen‐bonding networks involving carboxylate and H 2 bim ligands, leading to unique porous architectures with 1D channels accommodating lattice solvents. Thermogravimetric and variable‐temperature powder X‐ray diffraction analyses demonstrated the thermal stability and reversible hydration behavior of [ 1 ] 6 . AC impedance measurements under 100% relative humidity revealed high proton conductivity in [ 1 ] 6 , reaching 1.0 × 10 −2 S cm −1 at 358 K, attributable to proton transport facilitated by hydrogen‐bonded networks and lattice water molecules. Activation energy analysis suggested a vehicle mechanism for proton conduction. Overall, this study highlights the potential of hydrogen‐bonded cobalt complexes incorporating biimidazole ligands as promising proton‐conducting materials with tunable supramolecular architectures.