Hydrothermal synthesis
The synthesis of the crystal sample was performed following a reported method with minor modifications.28 0.1097 g (0.6 mmol) Zinc acetate, 0.1091 g (0.5 mmol) Pyromellitic dianhydride, 0.0781 g (0.5 mmol) 4,4’-Bipyridine and 10 mL deionized water were well mixed in a 25 mL Teflon-lined autoclave. Crystallization was carried out at 180 °C for 5 days. Then the autoclaves are cooled to room temperature. The crystals were filtered off, washed with hot water/ethanol mixture (1:1) for three times, then dried in air (yield: 0.1306 g, 76.1% based on Zinc acetate).
Rapid room temperature synthesis
0.1527 g (0.7 mmol) Pyromellitic dianhydride, 0.1093 g (0.7 mmol) 4,4’-Bipyridine and 5 mL deionized water were mixed in a 20 mL sealed vial with stirring at ambient temperature for 10 min, then 200 μL NH3·H2O (25%) was added into the vial. After the above mixture was thoroughly mixed, a 5 mL aqueous solution of 0.2569 g (1.4 mmol) Zinc acetate was added with stirring for 10 min. Then the products were filtered off, washed with hot water/ethanol mixture (1:1) three times, then dried in air (yield: 0.3288 g, 82.1% based on 4,4’-Bipyridine).