Inorganic–organic hybrids of the phosphotungstate Keggin anion and a Schiff base cation

Abstract

We present two organic–inorganic hybrids [C₉H₉N₄O]₃[PW₁₂O₄₀]·C₉H₈N₄O·4CH₃OH (1) and [C₉H₉N₄O]₃[PW₁₂O₄₀]·C₉H₈N₄O (2) consisting of 4-(salicylideneamino)-1,2,4-triazole cations and Keggin type phosphotungstate anions. Compounds 1 and 2 are characterized by NMR, UV-Vis, IR spectroscopy, and single-crystal X-ray diffraction studies. The crystal structures of compounds 1 and 2 show additional organic Schiff base molecules as lattice components. The analysis of the electron paramagnetic resonance (EPR) spectra of compounds 1 and 2 shows a peak at a g-value of 2.0023, characteristic of a free radical species. The attempted spin-trapping reaction of compound 2 with C₉H₁₈NO [(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)] resulted in the formation of single crystals of [C₉H₁₈NO]₃[PW₁₂O₄₀] (3) consisting of the TEMPOnium cation and phosphotungstate anion. Finally, compound 2 has been used as a radical initiator for free radical polymerization of styrene to polystyrene.