Unusual Thermal Expansion in Hydrogen Bonded Network of an Organic Salt Induced by Large Transverse Vibration of Atoms

Thermal expansion of an organic salt, prepared by solvent-drop grinding of terephthalic acid and imidazole in a 1:2 ratio, has been studied over a wide range of temperature 100–430 K. Restricted motion of the components in the hydrogen-bonded network resembles a fence-like structure led to a uniaxial negative thermal expansion (NTE). Interestingly, N–H···O hydrogen bonding distances remain almost unchanged over the temperature of study. Large transverse vibration of atoms involved in the hydrogen bonding plays an unprecedented role to keep the distances constant.