High-pressure crystal polymorph of the protic ionic liquid: Ethylammonium nitrate

Abstract A high pressure (HP) crystal polymorph was obtained for the protic ionic liquid ethylammonium nitrate (EAN). Crystal structures of the HP phases were determined by X-ray diffraction. The formation of either a single crystal or polycrystal depended on the temperature and pressure pathway. In a previous work, a low temperature (LT) crystal polymorph was identified, and multiple crystallization pathways were observed by simultaneous X-ray diffraction and differential scanning calorimetry measurements. The non-reversible HP-crystal polymorph was different from the LT-one. Despite the simple molecular structure of EAN, HP-crystal polymorph is observed in addition to LT-crystal polymorph and multiple LT-crystallization pathways.