High pressure studies of Ni₃[(C₂H₅N₅)₆(H₂O)₆](NO₃)₆·1.5H₂O by Raman scattering, IR absorption, and synchrotron X-ray diffraction

Herein, we report the high-pressure studies of Ni₃[(C₂H₅N₅)₆(H₂O)₆](NO₃)₆·1.5H₂O (1) by in situ Raman scattering, infrared absorption, and synchrotron angle-dispersive X-ray diffraction techniques up to ∼22 GPa at room temperature. We assigned all the vibration modes of 1 at ambient conditions. Detailed spectroscopy analyses revealed a chemical transformation at ∼0.75 GPa and a phase transition at ∼4.7 GPa, which are related to the behaviors of energetic ligands and flexible structures. Upon compression, the distortion of the energetic ligand induced the disconnection of NH₂ and the triazole ring at 0.75 GPa. Further analyses of the N-H vibration modes indicated the phase transition at 4.7 GPa accompanied with the rearrangement of hydrogen bonds. In addition, the lattice structure abnormally expanded above 8.6 GPa due to the deformation of nitrate ions and the extension of the triazole ring. This study helps to understand the properties and the behavior of energetic coordination complexes under high pressure.