Construction and proton conductivity of a POMs-based compound based on different isomers of [Mo8O26]4- ions

Abstract

POMs-based material compound 1 with two isomers of [Mo8O26]4- ions, H2[Cu(α-Mo8O26)0.5(β-Mo8O26)0.5(L1)3]·H2O (L1 = 1,4-bis(imidazole-l-ylmethyl)benzene), has been successfully synthesized. Compound 1 is a crystal containing the {Cu(L1)4} unit of windmill and the two [Mo8O26]4- are fixed to the {Cu(L1)4} unit through hydrogen bonding interactions. Compound 1 is an excellent proton conductor. According to the Nyquist plot of compound 1, at 30 ℃, the proton conductivity significantly increases with the increase of relative humidity. When the relative humidity increases to 90% RH, the proton conductivity is 1.85 × 10-3 S cm-1. At 90% RH, as the temperature increases, the resistance decreases and the proton conductivity increases. When the temperature reaches 80 ℃, the proton conductivity reaches 1.02 × 10-2 S cm-1. And according to the calculation of activation energy, it indicates that the proton conduction process of compound 1 follows the Grotthuss mechanism.