Two highly proton-conductive molecular hybrids based on ionized water clusters and poly-Keggin-anion chains

Two proton-conductive molecular hybrid complexes, {[Zn(H2O)8][H(H2O)2](HINO)4(PMo12O40)}n (1) and {[Mn(H2O)8][H(H2O)2.5](HINO)4(PMo12O40)}n (2), were constructed by introducing protonated water clusters, transition metal ionized water clusters and [PMo12O40]3− anions in the gallery of H-bonding networks based on isonicotinic acid N-oxide (HINO). Single-crystal X-ray diffraction analyses at 293 K revealed that both complexes presented exactly the same three-dimensional (3D) hydrogen-bonded networks with large one-dimensional (1D) channels. Interestingly, [PMo12O40]3− anions just filled in the 1D channels and self-assembled into poly-Keggin-anion chains. Thermogravimetric analyses both show 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. Surprisingly, the proton conductivities of 1 and 2 in the temperature range of 85–100 °C under 98% RH conditions reached high proton conductivities of 10−3 S cm−1. A possible mechanism of the proton conduction was proposed according to the experimental results.