*3.3. Synthesis of (Bu4N)4{SiW11O39[O(SiCH2CH2CH2NHCOR)2]} (R = -OC6H4NNC6H5NO2, Compound 2)*

When (*E*)-4-((4-nitrophenyl)diazenyl)phenyl (3-(triethoxysilyl)propyl)carbamate (0.77 g, 1.57 mmol) was dissolved in a solution of H2O/CH3CN (*v*/*v* = 20/60 mL) at room temperature, a turbid solution was formed to which K8SiW11O39·13H2O (1.95 g, 0.60 mmol) was added. The pH of the resulting reaction mixture was slowly adjusted to 0.7 with 1M HCl, and the clear solution was stirred overnight. Then, CH3CN was evaporated and NBu4Br (4.20 g, 13 mmol) was added to the aqueous solution to precipitate the expected product. The precipitate was collected and washed with deionized water (100 mL), ethanol (100 mL), and diethyl ether (100 mL) before being dried in a vacuum. Yield: 2.25 g (85.8%). IR (KBr, cm<sup>−</sup>1): ν = 3418 (m), 2961 (m), 2873 (m), 1742 (m), 1525 (m), 1485 (m), 1344 (m), 1205 (m), 1141 (w), 1044 (m), 964 (s), 947 (s), 904 (vs.), 856 (m), 804 (s), 535 (w). 1H NMR (CD3CN-*d*3, 400 MHz, ppm) δ = 8.32 (d, ArH, 4H), 7.97 (d, ArH, 4H), 7.97 (d, ArH, 4H), 7.92 (d, ArH, 4H), 7.31 (d, ArH, 4H), 3.29 (t, CH2, 4H), 3.12 (t, CH2, 32H), 1.86 (s, CH2, 4H), 1.62 (q, CH2, 32H), 1.37 (m, CH2, 32H), 0.97 (t, CH3, 48H), 0.76 (t, CH2, 4H). 13C NMR (CD3CN-*d3*, 100 MHz, ppm) δ = 156.6, 155.8, 155.0, 150.2, 149.7, 125.8, 125.3, 124.2, 123.7, 59.2, 44.1, 24.3, 24.0, 20.3, 13.9, 10.8. ESI-MS (negative mode, CH3CN): *m*/*z*: 1943 [**X2** + 2TBA]2<sup>−</sup>. Anal. Calcd. for C96H174N12O48Si3W11 (4370.96): C, 26.38; H, 4.01; N, 3.85; Found: C, 25.91; H, 4.02; N, 3.61.
