Crystal structures and proton conductivities of two molecular hybrids based on decorated poly-Keggin-anion chains

Abstract

Two proton-conductive molecular hybrid complexes, {[H(H₂O)₂][Sr(HINO)₄(H₂O)₇(PW₁₂O₄₀)]} _n (1) and {[H(H₂O)₂][Ca(HINO)₄(H₂O)₅(PW₁₂O₄₀)]} _n (2), were constructed by introducing alkaline-earth metal ions and [PW₁₂O₄₀]^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 reveal that both complexes crystallized in the orthorhombic space group Pnnm, and presented the same 3-D hydrogen-bonded networks with large 1-D channels. Interestingly, HINOs not only constructed 1-D hydrogen-bonded chains, but also coordinated to alkaline-earth metal ions to form decorated poly-Keggin-anions. In addition, decorated poly-Keggin-anion chains are also formed in the 1-D channels. Thermogravimetric analyses show no weight loss in the temperature range 20–70°C, indicating that all water molecules in the unit structure are not easily lost below 70°C. Surprisingly, the proton conductivities of 1 and 2 at 85–100°C under 98% relative humidity conditions reached good proton conductivities of 10⁻³ S cm⁻¹.

Keywords:

• Polyoxometalates
• Crystal structure
• Supramolecular complex
• Isonicotinic acid N-oxide
• Proton conductivity

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Nos. 20971038 and 21171050) and the Natural Science Foundation of the Education Department of Henan Province (2009A150015).