Dimensional Crossover and Proton Conductivity in Copper-Based Coordination Polymers by Coordinative Guest Insertion

Metal–organic materials (MOMs) are receiving widespread interest for use in many energy-related applications due to their tunable structure attained by the deliberate selection of metal and ligand components and their associated structure–property relationships. In this work, we demonstrate the dimensional crossover of discrete metal–organic polyhedra, CuMOP-3 (0-D, [Cu24(5-sip)24(S)24]·xS; 5-sip = 5-sulfoisophthalic acid, C8O7H5S), into Cu-based coordination polymers, CuCP-1 (2-D, [Cu(Im)4·Cu2(Im)4(5-sip)2]·2CH3OH) and CuCP-2 (3-D, [Cu4(μ3-OH)2(Im)2(5-sip)2]·2H2O), using the coordinative guest (imidazole (Im, C3N2H4) and H2O) insertion method. Specifically, the variation in the coordination environment at the metal center and secondary building units (SBUs) in response to these guest molecules as well as the changes in the coordination mode of the sulfonate (R-SO3–) functional group in the hemilabile 5-sip ligand induced overall structural and dimensionality changes. Furthermore, the transformation of dimensionality resulted in materials having improved thermal and chemical stabilities along with other physical properties (gas sorption and proton conductivity). This study introduces a new design strategy for achieving dimensional crossover in MOMs by involving both hemilabile organic linkers and coordinative guest insertions.