Polyoxometalate-driven assembly of inorganic-organic hybrid materials: Proton conductivity studies

A zinc-containing, one-dimensional coordination polymer, [Zn(NH(2)trz)(3)](NO3)(2) (1D-CP, NH2-trz = 4-amino-4H-1,2,4-triazole) has been employed to synthesize two water-insoluble proton conductors, ZnL-PW12 and ZnL-SiW12 (L = 4-amino-4H-1,2,4-triazole), that are formulated as {[Zn(NH(2)trz)(3)](NO3)}(2){HPW12O40}<middle dot>4H(2)O and [Zn(NH(2)trz)(3)][NH(3)trz](2)[SiW12O40]<middle dot>10H(2)O, respectively. These proton conductors were prepared through simple room-temperature aqueous reactions involving [Zn(NH(2)trz)(3)](NO3)(2) and phosphotungstic or silicotungstic acids, which proceed via aqueous disassembly of the CP, followed by recrystallization into a new phase driven by the addition of heteropolyanions. Here, the Keggin POMs, specifically H3PW12O40 and H4SiW12O40, impart enhanced stability to the overall structures of the resulting Zn-complex-POM adducts, ZnL-PW12 and ZnL-SiW12. Upon mixing the aqueous solutions of 1D-CP and POMs, immediate precipitations of the water-insoluble inorganic-organic hybrid products are obtained, the aqueous suspensions of which exhibit acidic pH. This observation prompted us to investigate proton conductivity behaviour of the resulting materials. As anticipated, the isolated products, ZnL-PW12 and ZnL-SiW12 exhibit significant proton conductivity values of 5.1 x 10(-3) and 5.6 x 10(-3) S cm(-1), respectively, at 80 degrees C and 98% relative humidity, demonstrating excellent stability for about 30 h with decent cycling stability over four heating-cooling cycles.