1 mmol of CuCl 2 (134.45 mg) in 2 ml of deionized water (light blue solution) and 1 mmol of 1,2,4-Triazole (69.07 mg) in 2 ml of deionized water (colorless solution) were mixed in a 20 mL glass vial and then kept in an oven at 60 • C for a day. The top part of the powdery sediment that contains relatively large crystals were pipetted out and casted in deionized water. The solution was shaken and left for 20-30 minutes until larger crystals were settled at the bottom, then, the supernatant containing smaller crystals was exchanged by fresh deionized water. After repeating the above decantation procedure 4-5 times, large crystals were preferably extracted and dried in an oven at 60 • C. The mass of the final product is typically 8-10 mg, 4-5 % of a precursor total mass of 203.52 mg, and about 40 % of the total mass of all crystals.