High-Pressure Stability of Energetic Crystal of Dihydroxylammonium 5,5'-Bistetrazole-1,1'-diolate: Raman Spectroscopy and DFT Calculations (original) (raw)
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The Journal of Physical Chemistry C, 2017
The structural response of a novel, insensitive energetic crystaldihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) was examined under high pressure. Using synchrotron single-crystal X-ray diffraction measurements, details of molecular, intermolecular, and crystal changes were determined to ∼10 GPa to understand its structural stability. The experimental results showed that TKX-50 exhibits highly anisotropic compression and significantly lower volume compressibility than currently known energetic crystals. These results are found to be in general agreement with our previous predictions from the DFT calculations. Additionally, the experimental data revealed anomalous compressionan expansion of the unit cell along the a axis (negative linear compressibility, NLC) upon compression to ∼3 GPa. The structural analyses demonstrated that this unusual effect, the first such observation in an energetic crystal, is a consequence of the highly anisotropic response of 3D motifs, comprised of two parallel anions [(C 2 N 8 O 2) 2− ] linked with two cations [(NH 3 OH) + ] through four strong hydrogen bonds. The present results demonstrate that the structural stability of TKX-50 is controlled by the strong and highly anisotropic intermolecular interactions, and these may contribute to its shock insensitivity.
High Pressure Raman Spectroscopy of Single Crystals of Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)
The Journal of Physical Chemistry B, 2007
To gain insight into the high-pressure polymorphism of RDX, an energetic crystal, Raman spectroscopy results were obtained for hydrostatic (up to 15 GPa) and non-hydrostatic (up to 22 GPa) compressions. Several distinct changes in the spectra were found at 4.0 (0.3 GPa, confirming the R-γ phase transition previously observed in polycrystalline samples. Detailed analyses of pressure-induced changes in the internal and external (lattice) modes revealed several features above 4 GPa: (i) splitting of both the A′ and A′′ internal modes, (ii) a significant increase in the pressure dependence of the Raman shift for NO 2 modes, and (iii) no apparent change in the number of external modes. It is proposed that the R-γ phase transition leads to a rearrangement between the RDX molecules, which in turn significantly changes the intermolecular interaction experienced by the NO bonds. Symmetry correlation analyses indicate that the γ-polymorph may assume one of the three orthorhombic structures: D 2h , C 2V , or D 2. On the basis of the available X-ray data, the D 2h factor group is favored over the other structures, and it is proposed that γ-phase RDX has a space group isomorphous with a point group D 2h with eight molecules occupying the C 1 symmetry sites, similar to the R-phase. It is believed that the factor group splitting can account for the observed increase in the number of modes in the γ-phase. Spatial mapping of Raman modes in a non-hydrostatically compressed crystal up to 22 GPa revealed a large difference in mode position indicating a pressure gradient across the crystal. No apparent irreversible changes in the Raman spectra were observed under non-hydrostatic compression.
The journal of physical chemistry. A, 2014
Raman spectroscopy was used to examine the vibrational and polymorphic behavior of 1,1-diamino-2,2-dinitroethene (FOX-7) to elucidate its structural and chemical stability under high pressure. Measurements were performed on single crystals compressed in a diamond anvil cell, and data were obtained over the entire frequency range of FOX-7 Raman activity. Several new features were observed with increase of pressure: (i) new vibrational peaks and discontinuity in the shifts of the peaks at 2 and 4.5 GPa, (ii) apparent coupling or mixing of several modes, and (iii) changes in the NH2 stretching spectral shape and modes shift. The spectral changes at 2 GPa, in contrast to previous reports, involved only a few peaks and likely resulted from a small molecular transformation. In contrast, changes at 4.5 GPa involved most of the modes, and the pressure for the onset and completion of the changes depended on the pressure medium. A large pressure hysteresis regarding the changes at 4.5 GPa imp...
Raman Spectroscopy of Pentaerythritol Single Crystals under High Pressures
The Journal of Physical Chemistry B, 2004
The effect of pressure on the Raman spectra of pentaerythritol (PE) single crystals was examined up to 10 GPa. Several abrupt changes in the spectra were found at 4.6 ( 0.2 GPa and 6.8 ( 0.3 GPa. These changes occur both in the internal and external modes and indicate the onset of phase transitions. Both transitions demonstrate considerable pressure hysteresis characteristic of a first-order phase change. It is concluded that PE crystals can exist in three different phases in the pressure range up to 10 GPa. Phase I, which has the bct structure, extends up to 4.6 GPa. In phase II, the number of translationally nonequivalent molecules in a PE unit cell is likely doubled. Phase III, above 6.8 GPa, has features of a disordered structure and is associated with a large softening of hydrogen bonding.
Crystals, 2018
Single-crystal samples of the semi-organic compounds mono-L-alaninium nitrate and monoglycine nitrate have been studied by Raman spectroscopy in a diamond-anvil cell up to 5.5 GPa, in order to observe the behavior of the deformation mode of NH 3 units. It was observed for these semi-organic crystals that increasing pressure produces a decrease in the wavenumber of the band associated with the deformation vibration, differently from most of the modes. Comparatively, mono-L-alaninium has a higher dν/dP than monoglycine nitrate, for the band associated with the deformation vibration. The anomalous behavior is explained in terms of the effect of high pressure in the short and linear intermolecular hydrogen bonds.
High-Pressure-Induced Phase Transitions in Pentaerythritol: X-ray and Raman Studies
The Journal of Physical Chemistry B, 2005
The high-pressure response of pentaerythritol crystals has been examined to 10 GPa in diamond-anvil cells using angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy. The results reveal two firstorder phase transitions: one at 4.8 GPa from phase I, tetragonal I4 h(S 4 2 ), to phase II, orthorhombic Pnn2(C 2V 10 ), with a small ∼0.5% volume change, and the other at 7.2 GPa to phase III with an unknown crystal structure. We found that phase I exhibits a large crystallographic anisotropy which rapidly decreases with increasing pressure: the ratio of linear compressibilities between two primary crystal axes decreases from o ) 8.1 at 1 atm to P ) 2.6 at 4 GPa. We suggest that this apparent decrease in crystal anisotropy is due to the disruption of hydrogen bonding in the (001) plane of phase I and eventually leads to an orthorhombic distortion from a quadrilateral network structure in phase I to a quasi one-dimensional structure in phase II. The crystal structure of phase III exhibits a disordered character, and it is likely a conformational variant of phase II.
Raman Studies of Molecular Crystals at High Pressures. IV. Acetonitrile,CH3CN andCD3CN
Journal of Raman Spectroscopy, 1996
The vibrations of solid tribromofluoromethane were studied by Raman scattering at room temperature and up to pressures of about 9 GPa. Changes in the low-wavenumber region of the Raman spectra reveal that freezing occurs near 1.0 GPa and that a solid-state phase transition occurs near 1.8 GPa. All of the internal modes are found to display splitting at elevated pressures, although only two modes (the CBr, asymmetric stretch v4 and the CF stretch vl) display splitting at the lowest pressures of the solid phase. The wavenumbers of the lattice and internal modes increase with applied pressure, except for the CF stretch mode vi, which decreases uniformly as the pressure increases.
The Journal of Physical Chemistry A, 2018
Samples of energetic material TEX (C 6 H 6 N 4 O 8) are studied using Raman spectroscopy and X-ray diffraction (XRD) up to 27 GPa pressure. There are clear changes in the Raman spectra and XRD patterns around 2 GPa related to a conformational change in the TEX molecule, and a phase transformation above 11 GPa. The molecular structures and vibrational frequencies of TEX are calculated by density functional theory based Gaussian 09W and CASTEP programs. The computed frequencies compare well with Raman spectroscopic results. Mode assignments are carried out using Vibrational Energy Distribution Analysis program, and also visualized in the Materials Studio package. Raman spectra of the high pressure phases indicate that the sensitivity of these phases is more than that of the ambient phase.
Journal of Physics: Conference Series, 2008
The contribution summarizes the results of recent studies of phase transitions induced by high pressure in a number of molecular organic crystals, such as polymorphs of paracetamol, chlorpropamide, polymorphs of glycine, L-and DL-serine, β-alanine. The main attention is paid to the following topics: (1) Reversible / irreversible transformations; (2) Different behavior of single crystals / powders; (3) The role of pressure-transmitting liquid; (4) The role of the kinetic factors: phase transitions on decompression, or after a long storage at a selected pressure; (5) Isosymmetric phase transitions; (6) The role of the changes in the hydrogen bond networks / intramolecular conformational changes in the phase transitions; (7) Superstructures / nanostructures formed as a result of pressure-induced phase transitions.
High-pressure Raman spectra of l-histidine hydrochloride monohydrate crystal
Vibrational Spectroscopy, 2011
Single-crystals of l-histidine hydrochloride monohydrate, C 6 H 9 N 3 O 2 ·HCl·H 2 O, were studied by Raman spectroscopy as a function of pressure in a diamond anvil cell up to 7.5 GPa at room temperature over the spectral range 3450-30 cm −1 . The effect of changing pressure on the vibrational spectrum is discussed. From the analysis of results we inferred that the crystal undergoes a reversible structural phase transition between 2.7 and 3.1 GPa. This transition is characterized by the splitting of a band related to torsion of CO 2 − , the disappearance and appearance of modes related with stretching of OH − and deformation of CO 2 − , as well as with bands of low wavenumber which are assigned as lattice modes, and by the discontinuities of the curves of wavenumber versus pressure. Pressure coefficients for all modes observed in this work are also given.