Imidazole Hidden Polar Phase

Transformations of NH···N hydrogen bonds can be employed in new classes of electronic materials. Imidazole, a prototypic NH···N bonded crystal, remains centrosymmetric when compressed to 2.7 GPa. However, its recrystallization at 1.2 GPa leads to a new polar phase which in turn can be decompressed to 0.5 GPa at least. This transformation and calculated potential-energy function of the H-atom correlate with the transforming dimensions of the hydrogen bond and reveal high polarity of nonionic NH···N bonded compounds