A Capping-assisted Strategy for Synthesis of Glass-like Carboxylate-based Coordination Polymers

The direct preparation of glass-like carboxylate-based coordination polymers (CPs) possessing continuous internal structure and transparency is challenging due to the lack of control on coordination kinetics and subsequently the range of order. Herein, a capping-assisted strategy was presented to control the molecular assembly during the metal-ligand coordination in the solution and to inhibit the long-range of order hence building glass-like CPs (g-CPs) mimicking the polymerization process. 1,3,5-benzene tricarboxylate (BTC) ligand was used to connect the copper cations (Cu2+) into metal-organic complexes of different Cu: BTC ratios (metal-organic pool) in presence of an excess of triethyl amine as a capping agent. Concentrating the Cu-BTC complexes and further drying under mild conditions induced the decapping process which triggered the random crosslinking between the free carboxylate and Cu2+ to form a boundary-free continuous internal structure. The as-prepared Cu-BTC g-CP exhibited an approximately similar fine structure like its crystalline counterpart (HKUST-1), which facilitated solvent and thermal-induced crystallization. Due to the internal structure continuity, the g-CP possesses ceramic-like hardness and wear resistance and plastic-like resilience. This capping-assisted strategy has been successfully extended to Ni-BTC and Fe-BTC systems under mild conditions and thus presenting a general method for the formation of glass-like carboxylate-based CPs.