A stable polyoxometalate-based porous coordination polymer with high proton conductivity

Abstract

A new coordination polymer based on the Keggin-type [SiW₁₂O₄₀]⁴⁻, namely, [Cu₄L₂(SiW₁₂O₄₀)(OH)₄(H₂O)₈]·8H₂O (1), has been prepared by a hydrothermal method (L = 1,4-bis(4H-1,2,4-triazol-4-yl)benzene). The supramolecular framework of 1 is constructed from two dimensional Cu–L layers. Compound 1 was found to be stable in aqueous solutions having pH values ranging from 1 to 13 as well as some other boiling solvents, such as boiling water, methanol and ethanol. Compound 1 exhibits a proton conductivity of 1.4 × 10⁻⁴ S cm⁻¹ at 65 °C and 98% RH. More importantly, the proton conductivity of 1 presents a 28-fold enhancement (3.9 × 10⁻³ S cm⁻¹ at 65 °C and 98% RH) by immersing its gourd-shaped channels into N₂H₄·H₂SO₄.