Synthesis and structure of a proton-conductive supramolecular complex based on poly-Keggin-anion chains

A proton-conductive organic/inorganic hybrid complex {[Cu(H2O)8][H(H2O)3](HINO)4(PW12O40)}n, was constructed by a self-assembly of H+(H2O)3 clusters, [Cu(H2O)8]2+ clusters, [PW12O40]3− anions and isonicotinic acid N-oxide (HINO). Single-crystal X-ray diffraction analysis at 293 K revealed that the title complex presented exactly a three-dimensional (3D) hydrogen-bonded network with large one-dimensional (1D) channels. Interestingly, [PW12O40]3− anions just filled in the 1D channels and self-assembled into poly-Keggin-anion chains. Thermogravimetric analysis shows no weight loss in the temperature range of 20–100 °C, indicating that all water molecules in the unit structure are not easily lost below 100 °C. The title complex was characterized by a satisfactory ionic conductivity (1–2 × 10−3 S cm−1) in the temperature range 85 to 100 °C only. However, it is two orders of magnitude lower than that of Nafion membrane. A possible mechanism of the proton conduction was proposed according to the experimental results.