3.2.1. Synthesis of [NH4]4[CuMo6O18(CH3C(CH2O)3)2]·5.5H2O (**1**)

A mixture of CuCl2·2H2O (0.34 g, 2.00 mmol), (NH4)6Mo7O24·4H2O (2.47 g, 2.00 mmol) and 0.48 g of CH3C(CH2OH)3 (0.48 g, 4.00 mmol) was dissolved in 20 mL of deionized water under stirring. The pH of the mixture was adjusted to 3~4 with the concentrated HCl, and the resulting solution was heated to 80 ◦C, and maintained for 2 h. After a hot filtration process, a blue solution was obtained, which provided blue crystals suitable for X-ray single-crystal diffraction analysis after about one day at room temperature. Elemental analysis calcd. (%) for [NH4]4[CuMo6O18(CH3C(CH2O)3)2]·5.5H2O (Mw = 1332.68 g mol<sup>−</sup>1): C 9.01%, H 3.40%, N 4.20%, Cu 4.77%, and Mo 43.19%; found C 9.20%, H 3.40%, N 4.25%, Cu 4.83%, and Mo 43.86%.
