*2.2. Syntheses* 2.2.1. Synthesis of **1**

Na9[A-α-PW9O34]·7H2O (0.320 g, 0.125 mmol) and NiCl2·6H2O (0.820 g, 3.44 mmol) were stirred in 9 mL 0.5 mol/L sodium acetate buffer (pH = 4.8) for 10 min; then, 3 mL DACH (Scheme 1a) was slowly dropped in and continually stirred for 30 min. The resulting solution was sealed in a 25 mL Teflon-lined stainless-steel autoclave and heated at 170 ◦C for 5 days. After cooling down to room temperature and washing with distilled water, green rod-like crystals were obtained with a yield of 34% (based on Na9[A-α-PW9O34]·7H2O). Elemental analysis calcd (%): C, 5.93; H, 3.26; and N, 2.30 (based on [Ni6(OH)3(DACH)3(H2O)6(PW9O34)] -·31H2O). Found: C, 7.10; H, 2.17; N, 2.81. IR(KBr, cm–1): 3428(s), 3332(w), 3280(w), 2929(w), 2856(w), 1628(w), 1588(w), 1449(w), 1377(w), 1231(w), 1119(w), 1039(s), 941(vs), 842(vs), 796(vs), and 716(vs).

**Scheme 1.** DACH (**a**), MIPA (**b**), and AA (**c**) ligands in **1**–**3**.
