Cyanoacetohydrazide under Pressure: Chemical Changes in a Hydrogen-Bonded Material.

Cyanoacetohydrazide (CAH, C3H5N3O) has been studied under pressure using diamond anvil cell techniques. CAH was characterized using Raman spectroscopy to 30 GPa and synchrotron X-ray diffraction to 45 GPa. The Raman spectra of CAH show reasonable qualitative agreement with first-principle calculations. The X-ray data reveal that CAH maintains its monoclinic structure to approximately 22 GPa with a density change of 12% over this range. Near 22 GPa, the Raman modes and most of the X-ray diffraction peaks disappear. These pressure-induced changes are irreversible upon the release of pressure, and the transformed sample can be recovered to ambient pressure. The recovered sample is photosensitive and shows reaction even at low laser powers of 10 mW at 532 nm. The paper concludes with observations of the roles of hydrogen bonding, molecular configurations, and the behavior of the cyano group in the pressure-induced changes in CAH.