Syntheses of Methylene‐bridged Symmetric Bisimidazolium Picrates as High‐energetic Salts

Symmetric bisimidazolium picrates were synthesized by the quaternization of bisimidazolylmethylene and a metathesis reaction with silver picrate. The symmetric structures of the new picrate salts were confirmed by H-1 and C-13 NMR spectral analysis and ESI-MS. The structures of compounds 3a and 4a were also confirmed by X-ray single crystal diffusion. The thermal properties of the compounds were determined by differential scanning calorimetry and thermogravimetric analysis. The picrates showed better thermal stabilities than did traditional azolium-based ionic salts, with higher decomposition temperatures, and 3b had the lowest melting point. These results indicated that the electronic effect of the substituent groups obviously influenced the quaternization and the high-energetic properties.