Pressure-dependent structure and electronic properties of energetic NTO crystals dominated by hydrogen-bonding interactions.

3-Nitro-1,2,4-trihydroxy-5-one (NTO), a highly potential high-performance explosive with good thermal stability and low sensitivity, has attracted much attention for its physicochemical properties in recent years. In this work, the pressure effect of the vibrational and electronic properties is investigated to understand the intermolecular interaction of NTO under hydrostatic compression. From the pressure-dependent Raman and infrared spectra, we found that the red-shifts of high-wavenumber N-H stretching modes and the discontinuous shifts of all Raman modes occur at 3 and 6 GPa, indicating an evident change of molecular configuration and intermolecular interaction upon compression. Based on structural analysis, the changes of intra- and intermolecular hydrogen bonds (HBs) are closely relevant to the anomalous rotation of the nitro group and the lengthening of N-H bonds, which can be treated as an important step of a potential structural transformation of NTO. Moreover, intermolecular hydrogen-bonding interaction leads to the shrinkage of the band gap at 6 GPa, caused by the fast charge transfer of 0.07 e from the nitrogen heterocycle to the nitro group. These results manifest a non-covalent interaction mechanism for modulating the molecular configuration of EMs under pressure loading and provide vital insights into understanding the pressure effects for energetic molecular crystals.