文摘
We report the high-pressure response of three forms (伪, 未, and 纬) of pyrazinamide (C5H5N3O, PZA) by in situ Raman spectroscopy and synchrotron X-ray diffraction techniques with a pressure of about 14 GPa. These different forms are characterized by various intermolecular bonding schemes. High-pressure experimental results show that the 纬 phase undergoes phase transition to the 尾 phase at a pressure of about 4 GPa, whereas the other two forms retain their original structures at a high pressure. We propose that the stabilities of the 伪 and 未 forms upon compression are due to the special dimer connection that these forms possess. On the other hand, the 纬 form, which does not have this connection, prefers to transform to the closely related 尾 form when pressure is applied. The detailed mechanism of the phase transition together with the stability of the three polymorphs is discussed by taking molecular stacking into account.