New organic-inorganic hybrid crystalline electrolytes comprised of 12-phosphotungstic acid (PWA) and the ionic liquid [1-butyl-3-methylimidazole][bis-(fluoromethanesulfonyl)amide] ([BMIM][TFSI]) with high thermal stability and high ion conductivity at high temperatures were obtained. In the new hybrids, there was a strong interaction between [BMIM](+) of the ionic liquid and PWA. The hybrids were very stable up to about 400 degrees C and showed a high ion jump during heating and cooling processes. Based on results from TG-DTA, DSC, and NMR spectroscopy, the ion jump was due to melting and solidification of the hybrid. The structures of powder and single-crystal samples of the hybrids were also studied. The chemical formula of the hybrid in the single crystal was determined to be PW13C32H56O54N8S0.16F0.26. This is nearly the same as those determined from the powder samples. By analyzing single-crystal X-ray diffraction (XRD) data, the hybrid was determined to crystallize in the space group Pca2(1) with the lattice constants a = 18.316(3), b = 18.327(3), and c = 16.657(3)angstrom. The powder XRD data of the hybrid were assigned. (c) 2008 Elsevier Ltd. All rights reserved.