Structural Characterization of 4-Cyanoimidazolium-5-olate, 4,4-Diphenyl-5-imidazolinone, and 4,5-Dicyanoimidazole. A Novel Mesoionic Compound and Decoding of Intermolecular Hydrogen Bonds

The present study on imidazole derivatives showed the mesoionic character of cyano-hydroxy derivative. The hydrogen bonding was also examined: (i) unusual hydrogen involving bonds for the 4-cyanoimidazolium-5-olate and 4,4-diphenyl-5-imidazolinone respectively, and (ii) formation of six hydrogen bonds for 4-cyanoimidazolium-5-olate, justifying the lack of a defined melting point, the high degradation temperature, the insolubility in organic solvent, and the IR properties. Nonlinear optical properties were also demonstrated. The efficiency of the second harmonic generation, the high thermal stability, the easy and economic synthesis and the transparency in visible region make the 4-cyanoimidazolium-5-olate an interesting candidate for nonlinear optics as single crystal.