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Crystal structure of 3,3′-(E)-diazene-1,2-diylbis{4-[(3,4-dinitro-1H-pyrazol-1-yl)-NNO-azoxy]-1,2,5-oxadiazole}

Published online by Cambridge University Press:  30 March 2021

A. O. Dmitrienko Open the ORCID record for A. O. Dmitrienko [Opens in a new window] ,
A. A. Konnov  and
M. S. Klenov
A. O. Dmitrienko*
Affiliation:
Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory, 119991Moscow, Russian Federation
A. A. Konnov
Affiliation:
N. D. Zelinsky Institute of Organic Chemistry Russian Academy of Sciences, Leninsky Prosp. 47, 119991 Moscow, Russian Federation
M. S. Klenov
Affiliation:
N. D. Zelinsky Institute of Organic Chemistry Russian Academy of Sciences, Leninsky Prosp. 47, 119991 Moscow, Russian Federation
*
a)Author to whom correspondence should be addressed. Electronic mail: dmitrienka@gmail.com
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Abstract

The crystal structure of a novel high-energy density material 3,3′-(E)diazene-1,2-diylbis{4-[(3,4-dinitro-1H-pyrazol-1-yl)-NNO-azoxy]-1,2,5-oxadiazole} (C10H2N18O12) was determined and refined using laboratory powder diffraction data. The title compound crystallizes in space group P21/c with a = 9.5089(3) Å, b = 11.6331(4) Å, c = 10.6270(3) Å, β = 116.2370(12), V = 1054.43(6) Å3. The asymmetric unit contains half of the molecule. The molecular conformation contains a weak intramolecular hydrogen bond C–H⋯O–N, both nitro groups are disordered, and the structure is dominated by weak O⋯π and O⋯O contacts.

Keywords

Rietveld refinementDFT calculationshigh-energy density materials
Type
Data Report
Information
Powder Diffraction , Volume 36 , Issue 2 , June 2021 , pp. 134 - 139
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Copyright
Copyright © The Author(s), 2021. Published by Cambridge University Press on behalf of International Centre for Diffraction Data

I. INTRODUCTION

X-ray powder diffraction techniques are routinely used in analysis of high-energy density materials. Their main objectives are phase analysis and the calculation of crystal density at room temperature. When single-crystal experiments are unavailable, they are also used to determine the crystal structure (and thus confirm the molecular structure) (Klenov et al., Reference Klenov, Anikin, Guskov, Churakov, Strelenko, Ananyev, Bushmarinov, Dmitrienko, Lyssenko and Tartakovsky2016).

High-energy density materials (HEDMs) containing azoxy groups are a subject of intensive research (Fischer et al., Reference Fischer, Klapötke, Reymann and Stierstorfer2014; Yu et al., Reference Yu, Wang, Yang, Wu, Lin, Ju, Lu and Cheng2015; Liu et al., Reference Liu, Zhang, Wang, Li, Zhang and Shreeve2016). However, only few (and not high-energy) compounds with an azoxy group bonded to a nitrogen atom of a heterocycle were reported (Moriarty et al., Reference Moriarty, Hopkins, Prakash, Vaid and Vaid1990; Semenov et al., Reference Semenov, Churakov, Chertanova, Strelenko, Ioffe and Tartakovskii1992). Additional N–N bonds can increase the enthalpy of formation and thus energy density. A two-dimentional molecular diagram for 3,3′-(E)-diazene1,2-diylbis{4-[(3,4-dinitro-1H-pyrazol-1-yl)-NNO-azoxy]-1,2,5-oxadiazole} (C10H2N18O12) is shown in Figure 1.

Figure 1. Molecular structure of the 3,3′-(E)-diazene-1,2-diylbis{4-[(3,4dinitro-1H-pyrazol-1-yl)-NNO-azoxy]-1,2,5-oxadiazole}.

II. EXPERIMENTAL

A. Safety precautions

Although we have encountered no difficulties during the preparation and handling of compound described in this paper, it is potentially explosive energetic material which is sensitive to impact and friction. Mechanical actions of this energetic material, involving scratching or scraping, must be avoided. Any manipulations must be carried out by using appropriate standard safety precautions (face shield, ear protection, body armor, Kevlar® gloves, and grounded equipment).

3,3′-(E)-Diazene-1,2-diylbis{4-[(3,4-dinitro-1H-pyrazol-1-yl)-NNO-azoxy]1,2,5-oxadiazole} was synthesized in three steps from known 1-amino-3,4-dinitropyrazole (Yin et al., Reference Yin, Zhang, He, Parrish and Shreeve2014) as part of Russian Science Foundation project 19-13-00276.

The compound is an impact and friction sensitive explosive, so caution is needed during sample preparation. The sample was ground in agate mortar in small (~5 mg) portions and placed between two Kapton films with a PTFE spatula.

The powder pattern was measured on a Bruker AXS D8 Advance Vario X-ray powder diffractometer equipped with a primary monochromator (CuK α 1, λ = 1.54056 Å) and 1D LynxEye PSD. Data were collected at room temperature in the range 6–90° 2θ with a 0.01° 2θ step size in the transmission mode (Figure 2).

Figure 2. Final observed (black), calculated (red) and difference profiles for the Rietveld refinement.

The diffraction pattern was indexed on a primitive monoclinic cell with a = 9.5089(3) Å, b = 11.6331(4) Å, c = 10.6270(3) Å, β = 116.2370(12) using the SVD (singular value decomposition) index algorithm (Coelho, Reference Coelho2003) as implemented in Bruker TOPAS 5.0 (Coelho, Reference Coelho2018), and space group determination was carried out using statistical systematic absences analysis as implemented in ExtSym (Markvardsen et al., Reference Markvardsen, Shankland, David, Johnston, Ibberson, Tucker, Nowell and Griffin2008). The resulting most probable space group P21/c was later confirmed by structure solution and refinement.

Parallel tempering, as implemented in FOX (Favre-Nicolin and Černý, Reference Favre-Nicolin and Černý2002), was used to solve the crystal structure in direct space. The Rietveld refinement (with Bruker TOPAS 5.0) was carried out using bond and angle restraints derived from periodic dispersion-corrected density functional theory (PW-DFT-D) calculations and a “riding” model for hydrogen atom. Restraint weight was automatically decreased during the refinement, and refinement result of more restrained model served as a starting structure for the next less restrained one. For detailed explanation of the methodology, see Dmitrienko and Bushmarinov (Reference Dmitrienko and Bushmarinov2015).

PW-DFT-D calculations were performed in VASP 5.4.4 (Kresse and Hafner, Reference Kresse and Hafner1993, Reference Kresse and Hafner1994; Kresse and Furthmüller, Reference Kresse and Furthmüller1996a, Reference Kresse and Furthmüller1996b) using the PBE functional (Perdew et al., Reference Sadovnichy, Tikhonravov, Voevodin and Opanasenko1996) corrected by Grimme D3 van der Waals correction (Grimme et al., Reference Grimme, Antony, Ehrlich and Krieg2010) with Becke-Jonson damping (Grimme et al., Reference Grimme, Ehrlich and Goerigk2011). A plane-wave basis set with “normal” projector augmented wave (PAW) pseudopotentials (Blöchl, Reference Blöchl1994; Kresse and Joubert, Reference Kresse and Joubert1999) as supplied with VASP was employed. All optimizations were performed using energy cutoff of 600 eV. Default 0.5 Å−1 k-point mesh and 8 k-points were used in all calculations.

Root-mean-square (rms) Cartesian displacement between the Rietveld refined structure and the PW-DFT-D optimized ones were calculated as suggested by Neumann (van de Streek and Neumann, Reference van de Streek and Neumann2014).

III. RESULTS AND DISCUSSION

The cell and molecular volume indicate Z′ = 1/2. Parallel tempering runs in FOX lead to two global minimization solutions with almost identical χ 2; views of their asymmetric units are shown on Figures 3 and 4. The only difference between the structures is the mutual arrangement of C-H and N-lone pair fragments of the pyrazole ring.

Figure 3. General view of 1 in a crystal.

Figure 4. General view of 2 in a crystal.

It is difficult to distinguish two 7 electron fragments given only diffraction data, but it can often be done by analyzing intermolecular contacts. Structure 2 contains highly unusual contact C-H⋯π with furazan ring with H⋯O distance of 2.09 Å (Figure 5). The shortest H⋯Oaromatic distance (with normalized C-H bond length) in the Cambridge Structural Database (CSD) is 2.15 Å and only 10 structures has H⋯O distance less than 2.3 Å. None of them are C-H⋯π interactions: the C-H bonds in all of them are almost parallel to the ring planes. It is unlikely that the structure contains such unprecedented contact; we should prefer structure 1.

Figure 5. Unusual contact in structure 2.

As an additional evidence, structures 1 and 2 were energy-optimized with PW-DFT-D in VASP with both fixed and free unit cell and the energies were compared. For structure 1, PW-DFT-D optimized energies are −603.410/−603.446 eV for fixed/relaxed cell calculations. For structure 2, optimized energies are −601.852/−601.979 eV. So structure 1 is more than 8 kcal/mol more energetically favorable.

Rietveld refinement was performed with fixed-cell energy-optimized structure 1 as source of bond and angle restraints. The N1O1O2 group got distorted during the refinement and thermal parameters for O1 and O2 became large when refined independently. A CSD search showed several hundreds of disordered nitro groups. So, we constructed and refined a disordered model; the occupancy of the minor component was close to 0.33. Even though no issues were found with distortion or thermal parameters of the second nitro group we added its minor component to the model to prevent short O⋯O contacts. That did not improve the R factors though. Final refinement with 108 variables and 69 restraints over 8017 data points yielded $R_{\rm p}/R_{\rm p}^{\prime}/R_{\rm wp}/R_{\rm wp}^{\prime}/{R_{\rm Bragg}}$ = 2.18/8.17/2.94/7.45/0.91%, GOF = 1.44 and occupancy of the minor component 0.378(11) (Figure 6).

Figure 6. Final refined structure with atom numbering. The atoms are represented by 50% probability spheroids.

Powder data can give us very few hints about disorder details. To check if our model makes sense, we optimized the minor component with PW-DFTD (in addition to already optimized major component). For it PW-DFT-D optimized energies are −603.372/−603.400 eV for fixed/relaxed cell calculations. The energy difference between components is as small as 0.25 kcal/mol, which is expected.

The root mean Cartesian displacement between free-cell energy-optimized structure and final Rietveld refined structure is 0.11 Å for the major component and 0.09 Å for the minor component, which is within the range expected for correct structures. Comparison of the final Rietveld refined structure with fixed-cell energy-minimized structures of major and minor components are shown on Figures 7 and 8.

Figure 7. Comparison of energy-optimized (orange) and Rietveld refined (green) major component of the disordered structure.

Figure 8. Comparison of energy-optimized (orange) and Rietveld refined (green) minor component of the disordered structure.

Figure 9 depicts the packing of 1. The shortest intermolecular contact in the structure is O⋯π interaction between the nitro group and the furozan cycle with O⋯O distance 2.769 Å. The only hydrogen atom participates in a weak C-H⋯O hydrogen bond with the azoxy group (C⋯O distance is 3.228 Å). Other notable contacts are NO2⋯O2N (O⋯O distance is 3.154 Å) and NO2⋯ONN (O⋯O distance is 3.134 Å). Lack of strong intermolecular interactions is typical for HEDMs.

Figure 9. Fragment of the crystal packing of 1 (view along the c axis).

IV. DEPOSITED DATA

The Crystallographic Information File (ak1696.cif) which contains the results of the Rietveld Refinement and the raw powder diffraction pattern, and six files (VASP_1_major_refined_cell.cif, VASP_1_minor_fixed_cell.cif, VASP_1_minor_refined_cell.cif, VASP_2_fixed_cell.cif, VASP_2_refined_cell.cif) related to the PW-DFT-D calculations using VASP were deposited with ICDD. The VASP files were used to obtain the bond length and angle restraints for structures 1 and 2, as discussed the EXPERIMENTAL section of this paper. These data files can be requested at info@icdd.com. The first file is also available from CCDC 2026495.

ACKNOWLEDGEMENTS

The study was funded by RFBR according to the research project № 1933-60075. M.S. Klenov and A. A. Konnov acknowledge financial support from Russian Science Foundation (project 19-13-00276) for the synthesis of the title compound. The in crystal calculations were carried out using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University (Sadovnichy et al., Reference Perdew, Burke and Ernzerhof2013).

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Figure 0

Figure 1. Molecular structure of the 3,3′-(E)-diazene-1,2-diylbis{4-[(3,4dinitro-1H-pyrazol-1-yl)-NNO-azoxy]-1,2,5-oxadiazole}.

Figure 1

Figure 2. Final observed (black), calculated (red) and difference profiles for the Rietveld refinement.

Figure 2

Figure 3. General view of 1 in a crystal.

Figure 3

Figure 4. General view of 2 in a crystal.

Figure 4

Figure 5. Unusual contact in structure 2.

Figure 5

Figure 6. Final refined structure with atom numbering. The atoms are represented by 50% probability spheroids.

Figure 6

Figure 7. Comparison of energy-optimized (orange) and Rietveld refined (green) major component of the disordered structure.

Figure 7

Figure 8. Comparison of energy-optimized (orange) and Rietveld refined (green) minor component of the disordered structure.

Figure 8

Figure 9. Fragment of the crystal packing of 1 (view along the c axis).