High-Pressure Structural Response of an Insensitive Energetic Crystal

Article pubs.acs.org/JPCC

High-Pressure Structural Response of an Insensitive Energetic Crystal: Dihydroxylammonium 5,5′-Bistetrazole-1,1′-diolate (TKX-50) Zbigniew A. Dreger,*,† Adam I. Stash,‡ Zhi-Gang Yu,† Yu-Sheng Chen,§ and Yuchuan Tao† †

Institute for Shock Physics and Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2816, United States ‡ State Scientific Center of Russian Federation, Karpov Institute of Physical Chemistry, 105064 Moscow, Russia § ChemMatCARS, The University of Chicago, Advance Photon Source, Argonne, Illinois 60439, United States S Supporting Information *

ABSTRACT: The structural response of a novel, insensitive energetic crystaldihydroxylammonium 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 compressionan 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 [(C2N8O2)2−] linked with two cations [(NH3OH)+] 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.

1. INTRODUCTION

There have been two reports on TKX-50 response under high pressure.6,7 A theoretical study by An et al.6 examined the mechanical response using large-scale molecular dynamics simulations. From calculated elastic limits for various shock directions, they suggested that TKX-50 can exhibit large anisotropic impact sensitivity with [100] as the least sensitive direction. They also calculated the pressure−volume dependence under static compression, obtaining a bulk modulus significantly larger than the bulk moduli reported for other HE crystals. In an earlier study,7 we investigated the high-pressure structural and chemical stability of TKX-50 by experimentally examining changes in the vibrational spectra and computationally examining changes in the unit cell parameters. In particular, our DFT calculations showed the compressibility to be highly anisotropic; the [100] axis exhibited strong incompressibility. Because the low-volume compressibility and the large anisotropy in compression may have important implications for the high-pressure stability/insensitivity, experimental data are needed to establish the compressive response of TKX-50 single crystals and to gain an in-depth understanding of its highpressure structural response. We used single-crystal X-ray diffraction measurements to obtain accurate and comprehensive

There is a continuing need for high-explosive (HE) crystals with higher energy release and lower sensitivity to initiation for various military and civilian applications. Therefore, significant efforts have been devoted to the design, synthesis, and characterization of new explosives with desirable characteristics.1 The recently synthesized dihydroxylammonium 5,5′bistetrazole-1,1′-diolate, also known as TKX-50, is an important step in this direction.2 This high nitrogen content, ionic crystal combines excellent performance with low sensitivity and is relatively easy to prepare. Its performance, in terms of detonation velocity, is superior to most of the currently used HEs, whereas its sensitivity to impact is 3−5 times lower than that of typical HEs, such as RDX (trimethylenetrinitramine) and PETN (pentaerythritol tetranitrate).2−4 These promising characteristics have attracted interest in understanding the underlying molecular processes in this crystal.5−10 Because the applications often involve shock wave compression, an understanding of its microscopic response at high-pressure (HP) and high-temperature (HT) conditions is important. In particular, detailed knowledge of the TKX-50 structural response is a key first step for understanding the molecular processes governing its stability at high pressures. However, the TKX-50 behavior at high pressures is relatively unexplored. © XXXX American Chemical Society

Received: January 26, 2017 Revised: February 23, 2017 Published: February 28, 2017 A

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Collection and integration of data were performed using the APEX II v. 2014.5-0 software suite.11 Structure determination and refinement were carried out using the SHELX software package.12 For all structures, thermal parameters were refined isotropically. Hydrogen atom positions were refined with DFT calculations using a periodic plane-wave pseudopotential method implemented in the Cambridge Serial Total Energy Package (CASTEP).13 The generalized gradient approximation (GGA) with the Perdew−Burke−Ernzerhof (PBE)14 parametrization and a plane-wave basis set with norm-conserving pseudopotential were used. van der Waals interactions were systematically taken into account via dispersion correction to the Kohn− Sham DFT energy developed by Grimme15 as implemented in CASTEP. Details of our computational and experimental approaches can be seen in refs 16 and 17.

structural data. Because the molecules in TKX-50 are linked together through an extensive network of hydrogen bonding (Figure 1), we carried out DFT calculations to refine the

3. RESULTS AND DISCUSSION 3.1. Unit Cell Parameters. Pressure-induced changes in the unit cell parameters are presented in Figure 2. In addition,

Figure 1. Molecular and crystal structure of TKX-50, P21/c space group, at ambient pressure and 295 K. (A) TKX-50 moiety: two cations (NH3OH)+ and an anion (C2N8O2)2−. Projection of two unit cells on the (110) plane (B) and on the (011) plane (C). Molecules are represented by the stick model. Hydrogen bonds are denoted by blue-dashed lines. Legend: carbon, gray; nitrogen, blue; oxygen, red; hydrogen, white. Crystal unit cells are represented by white lines.

position of hydrogen atoms for properly describing the hydrogen bonds. We determined the intra- and intermolecular distances and hydrogen-bonding parameters to gain insight into the molecular mechanisms governing structural stability of TKX-50 at high pressures. The paper is organized as follows. Experimental and computational methods are briefly described in the next section. Section 3 presents experimental results and discussions regarding the (i) pressure dependence of unit cell parameters, (ii) intra- and intermolecular bonding, and (iii) anomalous compressibility along the a axis. The main findings of this work are presented in section 4.

2. EXPERIMENTAL AND ANALYTICAL APPROACH TKX-50 single crystals were provided by Prof. T. Klapötke of Ludwig-Maximilian University (Munich, Germany). The crystals were used as grown but selected on the basis of quality and size to fit the high-pressure cell compartment. High pressures were generated using a modified Merrill−Bassett-type diamond-anvil cell. A rhenium gasket, preindented to 0.05 mm with a 0.12 mm hole drilled in the indentation, served as the sample compartment. Experiments were performed using a methanol/ethanol (4/1) mixture. Frequency shifts of the ruby R lines were used to monitor pressure in the sample compartment. The precision of our pressure measurements was estimated to be 0.05 GPa. High-pressure single-crystal X-ray diffraction measurements were carried out at ChemMatCARS (Sector 15) of the Advanced Photon Source, Argonne National Laboratory. All measurements were performed at room temperature. The beam energy was 30 keV, and the beam size at the sample was ∼(0.08 × 0.08) mm2. Data were collected using a Bruker D8 fixed-chi diffractometer equipped with an APEX II CCD detector.

Figure 2. Pressure dependence of unit cell parameters of TKX-50. Error bars are within the size of symbols.

the tabulated data are provided in Table S1. The results show that the ambient space group, P21/c, was maintained over the pressure range (to 10.3 GPa) examined. However, the changes in the lattice parameters demonstrated significant anisotropic compressibility. At 10 GPa, the lattice parameter changes were as follows (see Figure 3): +0.2% for the a axis, −12% for the b axis, and −8% for the c axis. Additionally, we observed anomalous compressibility along the a axis. Upon hydrostatic pressure, the a axis expands by 0.8% with a pressure increase to ∼3 GPa and then contracts with further pressure increase to 10 GPa. Thus, TKX-50 exhibits a negative compressibility up to ∼3 GPa and a positive compressibility above 4 GPa along the a axis. The structural origins of this unusual behavior along with the large anisotropic response are discussed in section 3.3. We compare our experimental data with previous theoretical results7 in Figure S1. Examination of that figure and Table S2 B

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Figure 3. Relative changes in the unit cell parameters of TKX-50. (Inset) Enlarged view of changes in the a axis. Figure 4. Pressure effects on intramolecular bond lengths in TKX-50. C−N bond represents the average value from the C1−N1 and C1−N4 bonds, whereas N−N bond represents the average value from the N1− N2, N2−N3, and N3−N4 bonds. Experimental data were fitted with linear curves. Estimated reductions in length over the range of 10 GPa were ∼2.9%, 2.8%, 1.5%, and 0.9% for the C−C, N5−O2, N−N, and C−N bonds, respectively.

reveals the good overall agreement between calculated and experimental parameters. The ambient values differ less than 2%, and the differences become smaller at higher pressures. The pressure trends are also well predicted by calculations with exception for the a axis. To compare the pressure−volume data with calculated results, the volume compressibility was analyzed in terms of a semiempirical equation of state (EOS). We used the third-order Birch−Murnaghan (3-BM) EOS,18 which is used often to evaluate the compressibility of energetic crystals.19 Although use of isotropic calcualtions for a strongly anisotropic crystal is not rigorously correct, we used this EOS because the same has been used extensively in the past. The fitting results are shown in Figure S2, and fitting parameters K0 (isothermal bulk modulus) and K′0 (pressure derivative of K0) are listed in Table 1. The DFT calculations7 underestimate the experimental data at low pressures, even with the use of a dispersion correction functional. Consequently, the calculated bulk modulus is considerably larger than the experimental value. Thus, the previously reported value of K0 for TKX-50, based on these calculations, was significantly overestimated.7 The experimental value of K0 = 21.9 GPa for TKX-50 is the largest value reported for any conventional or insensitive HE crystal. To date, the largest K0 reported for an HE crystal was 17.1 GPa for TATB,20 the accepted standard reference of IHEs that are also of good performance. Our present results confirm our previous computational predictions7 that TKX-50 is considerably stiffer than other HE crystals. The low compressibility of TKX-50, as pointed out previously,7 should result in a smaller temperature rise under shock compression in comparison to other HE crystals. Thus, TKX-50 should initiate at higher stress, in accord with its low impact sensitivity. 3.2. Intra- and Intermolecular Bonding. 3.2.1. Intramolecular Bonds. Pressure-induced changes for selected bonds are shown in Figure 4 to illustrate the trends. The results

represent the average values for the corresponding bonds length; labeling of atoms is given in Figure S3. Linear fits to the data show that all bonds display shortening with increasing pressure. Over the 10 GPa range, the largest reductions in length were observed for the C−C (anion) and N5−O2 (cation) bonds: 2.9% and 2.8%, respectively. The other bondsall located on the anionincluding the N1−O1 bond (not shown in the graph) were much less sensitive to pressure. Thus, the stability of anion and cation bonds can be affected differently with pressure. The large shortening of the C−C and N5−O2 bonds may imply their considerable strengthening. In contrast, small changes in other bonds may not increase their strength. Thus, pressure could stabilize the cation molecule more than the anion molecule, with the least stabilized bonds being in the tetrazole ring. 3.2.2. Hydrogen Bonding. The intermolecular bonding in TKX-50 is governed by the extensive network of intermolecular hydrogen bonds. Therefore, determination of pressure-induced changes in these bonds is important for understanding the crystal stability. In contrast to typical insensitive HE crystals, hydrogen bonds in TKX-50 are of different types and have very different strengths. The eight H bonds of four different types (N−H···N, N−H···O, O−H···O, and O−H···N) are depicted in Figure 5. As shown, each hydrogen atom of the cation is linked with two hydrogen atoms of the surrounding ions. Thus, the hydrogen bond network is composed of four different pairs of bonds. The hydrogen-bond assignment and their ambient parameters are presented in Table S3. Examination of the

Table 1. Bulk Moduli (K0) and Its Pressure-Derivative (K′0) for TKX-50 Using the Third-Order Birch−Murnaghan Equation experiment (this work)

DFT calculation (ref 7)

parameter

V0 fixed

V0 from fit

V0 fixed

V0 from fit

V0 (Å3) K0 (GPa) K′0

415.53 ± 0.11 21.9 ± 1.1 8.2 ± 0.7

415.63 ± 2.5 21.8 ± 3.1 8.2 ± 1.4

408.9 28.0 ± 0.3 7.0 ± 0.2

408.28 ± 0.38 29.1 ± 0.6 6.7 ± 0.2

C

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can play a major role in stabilizing the TKX-50 structure at high pressures. As discussed below, H bonds 1 and 4 are responsible for the extremely low and anomalous compressibility of TKX50 along the a axis. 3.3. Anomalous Compressibility of the a Axis Negative Linear Compressibility. Most materials contract in all directions when subjected to hydrostatic pressure. However, a small number of materials have been reported to expand in one direction under hydrostatic pressure, e.g., refs 22−24. Such expansion in one direction (termed negative linear compressibility, NLC) is unusual. However, NLC can provide useful insight into the structural foundations of materials.22 Although NLC has been reported in several inorganic compounds, and in metal−organic frameworks (see review, ref 24), only three organic crystals25−27 have shown NLC data. The a-axis expansion in TKX-50 reported here is the first NLC observation in a high-explosive crystal. To understand the a-axis expansion and its relation to structural stability, we examined the molecular and intermolecular changes under high pressure in more detail. Figure 7 shows the detailed crystal structure at ambient conditions. As shown in Figure 7A, the structure can be viewed as composed of quasi-layers along the a axis. These layers are comprised of 3D motifs formed by two bistetrazole anions, (C2O2N8)2−, bonded with two hydroxylammonium cations, (NH3OH)+, via two pairs of hydrogen bonds. Two molecules of the cation are located on opposite sides of the plane (001), which passes through the middle of two molecules of the anion. Next, we examined pressure-induced changes in several parameters of the 3D motif. These parameters, labeled in Figure 7B, include distances between ions, the angle between the cation and two anions, and the lengths and angles of H bonds. The pressure dependence of these parameters (Figure 8) reveals several characteristic features. The distance between two cations, l, decreases substantially, in accord with the increasing angle, θ, between the nitrogen atom of the cation and the oxygen atoms of two anions. In contrast, distances

Figure 5. Hydrogen-bond network in TKX-50 crystal. Anions (C2O2N8)2−and cations (NH3OH)+ are linked by eight different bonds. Bonds are indicated by the blue dashed lines and numbers. Assignment of bonds is given in Table S2.

lengths and angles reveals that the bonds contributing to the same pair can have considerably different strengths.21 The most prominent cases are the pairs of bonds 1−2 and 3−4. Bonds 1 (O−H···O) and 4 (N−H···O) are the strongest, whereas bonds 2 (O−H···N) and 3 (N−H···N) are among the weakest bonds. Pressure-induced changes in the lengths and angles of H bonds are presented in Figure 6. As pressure increases, the lengths of all bonds decrease. The extent of the decrease varies among different bonds and is larger for the long bonds than for the short bonds. In contrast, the angles are less sensitive to pressure. Apart from bonds 3 and 4, angles of the other bonds barely change with pressure. Further examination of changes for the individual bonds indicates that all hydrogen bonds, except bonds 2 and 4, will increase their strength under pressure. Bond 2 will likely remain unchanged, and bond 4 will decrease in strength at higher pressures. Despite the above changes, the hydrogen-bonding network in TKX-50 maintains the same motif but with a considerably increased strength at higher pressures. Furthermore, bonds 1 and 4 remain significantly stronger than all other bonds. Therefore, they

Figure 6. Pressure effects on hydrogen-bond length (a) and angle (b). Solid and open symbols of the same color represent bonds corresponding to the same hydrogen atom of the cation. Assignment of bonds to numbers is given in Table S3. Experimental data are connected with lines to guide the eye. D

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pressure. The length decrease can lead to the increase of bond strength; however, the angle decrease can reduce the extent of this increase. From the discussion above, the observed NLC and the anomaly in compressibility at 3 GPa can be attributed to the interplay between the different pressure response of the interand intramolecular interactions in the TKX-50 framework. With increasing pressure, distance between the cations along the b axis decreases substantially due to the weak interlayer interactions. This decrease is accompanied by an increase of the θ angle and compression of the strong, HB-1 and HB-4, hydrogen bonds. As a result, the bistetrazole anion molecules are pushed back by the “rigid” hydrogen bonds, resulting in the a-axis expansion or NLC along this direction. The change from NLC to positive linear compressibility (PLC) at ∼3 GPa can be related to the further changes in the hydrogen bond strength. Figures 8 and 9 show that the initial Figure 7. (A) Structure of TKX-50 viewed along the c-axis direction. Dashed white lines outline the borders between layer-like structures. Layers are comprised of chains of 3D motifs along the a axis. Motifs are formed by two parallel anion molecules linked with two cations via four strong hydrogen bonds, denoted by the blue lines. (B) View of 3D unit. Dashed white lines indicate different parameters of the unit. Parameters used to characterize the unit cell: distance between oxygen atoms (O1) located on adjacent anions (w), distance between nitrogen atoms (N5) located on two cations (l), distance between two oxygen atoms located on the same anion (h), and angle between oxygen atoms of two anions and nitrogen atom of cation, ∠O1N5O1, (θ). HB-1 and HB-4 are labels of hydrogen bonds.

Figure 9. Comparison of pressure effects on the a-axis dimension with changes in the HB-4 hydrogen bond.

pressure increase can strengthen both hydrogen bonds by decreasing the H-bond distance and cause NLC. However, as pressure approaches ∼3 GPa, the two bonds can experience opposite trends. The HB-1 bond continues strengthening, but the HB-4 bond shows weakening. The weaker HB-4 bonds can reduce the compression exerted on the anion molecules, leading to the reversal from NLC to PLC. NLC and its reversal to PLC are also coupled to the vibrational response. As seen in Figure S4, a number of Raman modes show distinct behavior around ∼3 GPa. The lattice vibrations display evidently the change in the Raman shift slope, whereas the intramolecular modes exhibit a clear coupling between vibrations localized on the anion and cation molecules. Thus, this result demonstrates that the anomalous compressibility behavior of TKX-50 can affect other molecular properties. In particular, it emphasizes the important role that hydrogen bonding can play in coupling the mechanical and vibrational responses. Because the vibrational coupling may contribute to insensitivity of shocked IHE crystals,7,16,17,28 the findings here provide a potential mechanism for the coupling of molecular vibrations in the TKX-50 crystal.

Figure 8. (A) Pressure effects on different dimensions of the 3D unit. (B) Pressure effects on the distance and angle of hydrogen bonds (HB-1 and HB-4) linking the anions with cations.

between nitrogen atoms of the same anion, h, and between nitrogen atoms of the adjacent anions, w, show significantly smaller pressure dependence. The distance between the anion molecules, w, measured along the a axis displays nonmonotonic dependence, similar to the changes in the a-axis length. Pressure effects on the two hydrogen bonds that link the anions and cations in the 3D unit are shown in Figure 8B. In both cases, the length and angle of these bonds decrease with E

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4. SUMMARY Using high-pressure, synchrotron single-crystal X-ray diffraction measurements, we demonstrated highly anisotropic compressibility of a novel insensitive energetic crystal, TKX-50. Detailed structural analyses revealed that the large anisotropic response could be attributed to the presence of weakly bonded (010) quasi-layers comprised of strongly bonded 3D motifs aligned along the a axis. These motifs are formed by two bistetrazole anions bonded with two hydroxylammonium cations through two pairs of strong hydrogen bonds. We found that this framework leads to anomalous compressibility along the acrystallographic direction, including negative linear compressibility (NLC) to ∼3 GPa. The NLC effect is attributed to the interplay between different pressure responses of the inter- and intramolecular interactions in the chains of 3D motifs. Changes in the strength of hydrogen bonds linking two bistetrazole anions with two hydroxylammonium cations are proposed to govern the anomalous compressibility, low volume compressibility, molecular vibrations coupling, and strong structural stability of TKX-50 at high pressures. The detailed crystal structures and anomalous compression behavior revealed in this study are important for gaining microscopic insight into insensitivity of TKX-50.

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supported by the U.S. DOE under Contract No. DE-AC0206CH11357.

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(1) Klapötke, T. M. Chemistry of High-Energy Materials, 3rd ed.; DeGruyter & Co.: Berlin, 2015. (2) Fischer, N.; Fischer, D.; Klapötke, T. M.; Piercey, D. G.; Stierstorfer, J. Pushing the Limits of Energetic Materials - the Synthesis and Characterization of Dihydroxylammonium 5,5′-bistetrazole-1,1′diolate. J. Mater. Chem. 2012, 22, 20418−20422. (3) Klapötke, T. M.; Fischer, N.; Fischer, D.; Klapötke, T. M.; Piercey, D. G.; Stierstorfer, J.; Reymann, M. Energetic Active Composition Comprising a Dihydroxylammonium Salt or Diammonium Salt of a Bistetrazolediol. US Patent 20140171657A1, June 19, 2014. (4) Golubev, V. K.; Klapötke, T. M. Comparative Analysis of Shock Wave Action of TKX-50 and Some other Explosives on Various Barriers. New Trends Res. Energy Mater. Proc. Semin., 17th 2014, 2, 672−676. (5) An, Q.; Liu, W.-G.; Goddard, W. A., III; Cheng, T.; Zybin, S. V.; Xiao, H. Initial Steps of Thermal Decomposition of Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate Crystals from Quantum Mechanics. J. Phys. Chem. C 2014, 118, 27175−27181. (6) An, Q.; Cheng, T.; Goddard, W. A., III; Zybin, S. V. Anisotropic Impact Sensitivity and Shock Induced Plasticity of TKX-50 (Dihydroxylammonium 5,5′-bis(tetrazole)-1,1′-diolate) Single Crystals: From Large-Scale Molecular Dynamics Simulations. J. Phys. Chem. C 2015, 119, 2196−2207. (7) Dreger, Z. A.; Tao, Y.; Averkiev, B. B.; Gupta, Y. M.; Klapötke, T. M. High-Pressure Stability of Energetic Crystal of Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50): Raman Spectroscopy and DFT Calculations. J. Phys. Chem. B 2015, 119, 6836−6847. (8) Huang, H.; Shi, Y.; Yang, J. Thermal Characterization of the Promising Energetic Material TKX-50. J. Therm. Anal. Calorim. 2015, 121, 705−709. (9) Meng, L.; Lu, Z.; Wei, X.; Xue, X.; Ma, Y.; Zeng, Q.; Fan, G.; Nie, F.; Zhang, C. Two-sided Effects of Strong Hydrogen Bonding on the Stability of Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX50). CrystEngComm 2016, 18, 2258−2267. (10) Ma, S.; Li, Y.; Li, Y.; Luo, Y. Research on Structures, Mechanical Properties, and Mechanical Responses of TKX-50 and TKX-50 Based PBX with Molecular Dynamics. J. Mol. Model. 2016, 22, 384−394. (11) APEX 2; Bruker AXS Inc.: Madison, WI, 2014. (12) Sheldrick, G. M. SHELX, Program for Crystal Structure Solution; University of Gottingen: Gottingen, Germany, 2013. (13) Clark, S. J.; Segall, M. D.; Pickard, C. J.; Hasnip, P. J.; Probert, M. J.; Refson, K.; Payne, M. C. First Principles Methods using CASTEP. Z. Kristallogr. - Cryst. Mater. 2005, 220, 567−570. (14) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (15) Grimme, S. Semiempirical GGA-type Density Functinal Constructed with a Long-Range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787−1799. (16) Dreger, Z. A.; Stash, A. I.; Yu, Z.-G.; Chen, Y.-S.; Tao, Y.; Gupta, Y. M. High- Pressure Crystal Structures of an Insensitive Energetic Crystal: 1,1-Diamino-2,2- dinitroethene. J. Phys. Chem. C 2016, 120, 1218−1224. (17) Dreger, Z. A.; Stash, A. I.; Yu, Z.-G.; Chen, Y.-S.; Tao, Y.; Gupta, Y. M. High- Pressure Structural Response of an Insensitive Energetic Crystal: 1,1-Diamino-2,2- dinitroethene (FOX-7). J. Phys. Chem. C 2016, 120, 27600−27607. (18) Birch, F. Finite Elastic Strain of Cubic Crystals. Phys. Rev. 1947, 71, 809−824. (19) Peiris, S. M.; Gump, J. C. In Static Compression of Energetic Materials; Peiris, S. M.; Piermarini, G. J., Eds.; Springer-Verlag: Berlin Heildelberg, 2008; Chapter 3, pp 99−126. (20) Stevens, L. L.; Velisavljevic, N.; Hooks, D. E.; Dattelbaum, D. M. Hydrostatic Compression Curve for Triaamino-Trinitrobenzene

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.7b00867. Experimental and calculated unit cell parameters under high pressure; labeling of atoms in molecules; assignment of hydrogen bonds; fitting of experimental and calculated unit cell volumes to the third-order Birch−Murnaghan equation of state; comparison of pressure effect on the aaxis dimension with Raman shifts of selected modes (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: 509-335-4233. ORCID

Zbigniew A. Dreger: 0000-0001-9541-0827 Zhi-Gang Yu: 0000-0002-1376-9025 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Prof. Y. M. Gupta is thanked for supporting this work and for many valuable comments on this manuscript. We also thank Prof. T. M. Klapötke from Ludwig-Maximilian University of Munich for providing the TKX-50 crystals. The work of Z.A.D. and Y.T. was supported by DOE/NNSA (DE-NA0002007) and ONR (N000014-16-1-2088). Experiments were performed at the ChemMatCARS Sector 15 of the Advanced Photon Source, Argonne National Laboratory. The ChemMatCARS Sector 15 is principally supported by the Divisions of Chemistry (CHE) and Materials Research (DMR), National Science Foundation, under grant number NSF/CHE-1346572. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was F

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