Synthesis, crystal structure and thermal properties of an unsymmetrical 1,2,4,5-tetra­zine energetic derivative

Chen, X.; Zhang, C.; Bai, Y.; Guo, Z.; Yao, Y.; Song, J.; Ma, H.

doi:10.1107/S2053229618006617

Synthesis, crystal structure and thermal properties of an unsymmetrical 1,2,4,5-tetrazine energetic derivative

X. Chen, C. Zhang, Y. Bai, Z. Guo, Y. Yao, J. Song and H. Ma

A new unsymmetrical s-tetrazine derivative, namely 4-({2-[6-(3,5-dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazin-3-yl]hydrazin-1-ylidene}methyl)phenol (DPHM), C₁₄H₁₄N₈O, was synthesized based on 3-(3,5-dimethylpyrazol-1-yl)-6-hydrazinyl-s-tetrazine (DPHT). The structure was characterized by elemental analysis and single-crystal X-ray diffraction. Crystal structure determination shows that DPHM crystallizes in the monoclinic P2₁/c space group with high coplanarity and a zigzag layered structure. In addition, its thermal behaviour was investigated by DSC and TG–DTG methods. The thermal safety of DPHM was evaluated by self-accelerating decomposition temperature (T_SADT), critical temperature of thermal explosion (T_b), entropy of activation (ΔS $^{\neq}$ ), enthalpy of activation (ΔH $^{\neq}$ ) and free energy of activation (ΔG $^{\neq}$ ). Meanwhile, the kinetic parameters and specific heat capacity of DPHM were also determined. The results show that DPHM has better stability and detonation properties than 3-(2-benzylidenehydrazin-1-yl)-6-(3,5-dimethylpyrazol-1-yl)-s-tetrazine (DAHBTz), due to the introduction of a hydroxy group, which increases the number of hydrogen-bond interactions and improves the stability and density of DPHM. This study demonstrates that the performance of an explosive can be optimized through structural modification.

Keywords: unsymmetrical s-tetrazine; crystal structure; hydrogen-bond interactions; thermal properties; molecular stability; detonation properties; 1,2,4,5-tetrazine; energetic material.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S2053229618006617/qs3070sup1.cif Contains datablocks global, I
	Structure factor file (CIF format) https://doi.org/10.1107/S2053229618006617/qs3070Isup2.hkl Contains datablock I

CCDC reference: 1815376

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008b); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

4-({2-[6-(3,5-Dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazin-3-yl]hydrazin-1-ylidene}methyl)phenol top

Crystal data top

C₁₄H₁₄N₈O	F(000) = 648
M_r = 310.33	D_x = 1.432 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 5.8043 (16) Å	Cell parameters from 1328 reflections
b = 31.562 (9) Å	θ = 2.7–23.3°
c = 7.898 (2) Å	µ = 0.10 mm⁻¹
β = 95.860 (6)°	T = 296 K
V = 1439.3 (7) Å³	Block, red
Z = 4	0.36 × 0.27 × 0.13 mm

Data collection top

Bruker APEXII CCD diffractometer	1640 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.039
φ and ω scans	θ_max = 25.1°, θ_min = 2.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 2008a)	h = −6→6
T_min = 0.679, T_max = 0.746	k = −37→36
7247 measured reflections	l = −9→8
2552 independent reflections

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.059	H-atom parameters constrained
wR(F²) = 0.179	w = 1/[σ²(F_o²) + (0.0822P)² + 0.8073P] where P = (F_o² + 2F_c²)/3
S = 1.05	(Δ/σ)_max < 0.001
2552 reflections	Δρ_max = 0.36 e Å⁻³
209 parameters	Δρ_min = −0.35 e Å⁻³

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Unit cell dimensions were obtained with least-squares refinements and semi-empirical absorption corrections were applied using the SADABS program (Sheldrick, 2008a). The structure was solved by direct methods and refined by full-matrix least squares techniques based on F² with the SHELXTL and OLEX² program (Sheldrick, 2008b; Dolomanov et al., 2009). All non-hydrogen atoms were obtained from the difference Fourier map and refined with atomic anisotropic thermal parameters.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
N1	0.4725 (4)	0.17854 (8)	0.9759 (4)	0.0458 (7)
N2	0.6592 (4)	0.15510 (8)	1.0433 (3)	0.0394 (6)
N3	0.4779 (4)	0.09682 (8)	0.9071 (3)	0.0437 (7)
N4	0.4834 (4)	0.05731 (8)	0.8544 (3)	0.0435 (7)
N5	0.8530 (4)	0.08987 (8)	1.0552 (3)	0.0397 (6)
N6	0.8598 (4)	0.04984 (8)	1.0057 (3)	0.0403 (7)
N7	0.7035 (4)	−0.00418 (8)	0.8395 (4)	0.0438 (7)
H7	0.8273	−0.0184	0.8694	0.053*
N8	0.5285 (4)	−0.02186 (8)	0.7307 (3)	0.0424 (7)
O1	−0.0617 (4)	−0.15167 (8)	0.2356 (3)	0.0628 (7)
H1	−0.1797	−0.1384	0.2040	0.094*
C1	0.3394 (7)	0.25160 (11)	0.9954 (5)	0.0625 (11)
H1A	0.3935	0.2772	1.0518	0.094*
H1B	0.3227	0.2561	0.8745	0.094*
H1C	0.1922	0.2439	1.0318	0.094*
C2	0.5100 (5)	0.21682 (10)	1.0389 (4)	0.0450 (8)
C3	0.7182 (6)	0.21879 (10)	1.1458 (5)	0.0499 (9)
H3	0.7801	0.2425	1.2040	0.060*
C4	0.8124 (5)	0.17896 (9)	1.1475 (4)	0.0416 (8)
C5	1.0308 (6)	0.16287 (11)	1.2399 (5)	0.0542 (9)
H5A	1.0485	0.1334	1.2147	0.081*
H5B	1.1597	0.1784	1.2046	0.081*
H5C	1.0254	0.1664	1.3602	0.081*
C6	0.6658 (5)	0.11239 (9)	0.9989 (4)	0.0355 (7)
C7	0.6805 (5)	0.03535 (9)	0.8988 (4)	0.0365 (7)
C8	0.5669 (5)	−0.05909 (10)	0.6790 (4)	0.0414 (8)
H8	0.7065	−0.0722	0.7158	0.050*
C9	0.3971 (5)	−0.08178 (9)	0.5631 (4)	0.0391 (7)
C10	0.4444 (5)	−0.12280 (10)	0.5134 (4)	0.0457 (8)
H10	0.5838	−0.1353	0.5550	0.055*
C11	0.2902 (6)	−0.14537 (10)	0.4042 (4)	0.0486 (8)
H11	0.3260	−0.1728	0.3723	0.058*
C12	0.0809 (5)	−0.12707 (11)	0.3418 (4)	0.0442 (8)
C13	0.0292 (5)	−0.08607 (10)	0.3881 (4)	0.0442 (8)
H13	−0.1101	−0.0737	0.3454	0.053*
C14	0.1856 (5)	−0.06362 (10)	0.4980 (4)	0.0427 (8)
H14	0.1500	−0.0362	0.5291	0.051*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.0389 (15)	0.0446 (16)	0.0509 (17)	0.0087 (12)	−0.0098 (13)	0.0000 (13)
N2	0.0338 (14)	0.0378 (14)	0.0441 (16)	0.0018 (11)	−0.0079 (12)	0.0006 (12)
N3	0.0362 (15)	0.0416 (15)	0.0504 (18)	−0.0002 (12)	−0.0095 (13)	−0.0018 (12)
N4	0.0372 (15)	0.0399 (15)	0.0504 (17)	−0.0006 (11)	−0.0097 (13)	−0.0015 (12)
N5	0.0359 (14)	0.0373 (14)	0.0435 (16)	0.0001 (11)	−0.0078 (12)	−0.0024 (12)
N6	0.0372 (14)	0.0364 (14)	0.0449 (16)	−0.0001 (11)	−0.0074 (12)	−0.0014 (12)
N7	0.0377 (15)	0.0371 (15)	0.0529 (18)	0.0005 (11)	−0.0131 (13)	−0.0055 (12)
N8	0.0384 (15)	0.0412 (15)	0.0447 (16)	−0.0052 (12)	−0.0094 (12)	−0.0022 (12)
O1	0.0475 (15)	0.0693 (17)	0.0659 (17)	−0.0054 (12)	−0.0220 (13)	−0.0176 (14)
C1	0.059 (2)	0.050 (2)	0.076 (3)	0.0151 (18)	−0.007 (2)	0.0031 (19)
C2	0.0427 (19)	0.0389 (18)	0.052 (2)	0.0051 (15)	0.0001 (16)	0.0059 (15)
C3	0.047 (2)	0.0385 (18)	0.062 (2)	0.0008 (15)	−0.0065 (17)	−0.0014 (16)
C4	0.0390 (17)	0.0351 (17)	0.048 (2)	−0.0022 (14)	−0.0066 (15)	−0.0008 (14)
C5	0.044 (2)	0.0443 (19)	0.068 (2)	−0.0015 (15)	−0.0216 (18)	−0.0049 (17)
C6	0.0334 (16)	0.0363 (16)	0.0353 (17)	−0.0016 (13)	−0.0036 (13)	0.0018 (13)
C7	0.0327 (16)	0.0383 (17)	0.0364 (18)	−0.0027 (13)	−0.0059 (14)	0.0038 (13)
C8	0.0351 (17)	0.0406 (18)	0.046 (2)	−0.0015 (13)	−0.0070 (15)	−0.0001 (15)
C9	0.0354 (16)	0.0430 (18)	0.0373 (18)	−0.0031 (14)	−0.0044 (14)	0.0018 (14)
C10	0.0359 (17)	0.0485 (19)	0.050 (2)	0.0055 (14)	−0.0114 (15)	−0.0051 (15)
C11	0.0457 (19)	0.0410 (18)	0.056 (2)	0.0016 (15)	−0.0080 (16)	−0.0108 (16)
C12	0.0364 (17)	0.056 (2)	0.0382 (19)	−0.0075 (15)	−0.0069 (14)	−0.0036 (15)
C13	0.0305 (16)	0.053 (2)	0.046 (2)	0.0032 (15)	−0.0082 (15)	0.0045 (16)
C14	0.0372 (17)	0.0407 (18)	0.049 (2)	0.0018 (14)	−0.0043 (15)	0.0020 (15)

Geometric parameters (Å, º) top

N1—N2	1.373 (3)	C2—C3	1.403 (4)
N1—C2	1.317 (4)	C3—H3	0.9300
N2—C4	1.373 (4)	C3—C4	1.370 (4)
N2—C6	1.395 (4)	C4—C5	1.486 (4)
N3—N4	1.316 (3)	C5—H5A	0.9600
N3—C6	1.340 (4)	C5—H5B	0.9600
N4—C7	1.353 (4)	C5—H5C	0.9600
N5—N6	1.324 (3)	C8—H8	0.9300
N5—C6	1.336 (4)	C8—C9	1.462 (4)
N6—C7	1.351 (4)	C9—C10	1.388 (4)
N7—H7	0.8600	C9—C14	1.404 (4)
N7—N8	1.380 (3)	C10—H10	0.9300
N7—C7	1.344 (4)	C10—C11	1.376 (4)
N8—C8	1.271 (4)	C11—H11	0.9300
O1—H1	0.8200	C11—C12	1.389 (5)
O1—C12	1.360 (4)	C12—C13	1.386 (4)
C1—H1A	0.9600	C13—H13	0.9300
C1—H1B	0.9600	C13—C14	1.385 (4)
C1—H1C	0.9600	C14—H14	0.9300
C1—C2	1.495 (4)

C2—N1—N2	104.7 (3)	H5A—C5—H5B	109.5
N1—N2—C6	117.7 (2)	H5A—C5—H5C	109.5
C4—N2—N1	112.0 (2)	H5B—C5—H5C	109.5
C4—N2—C6	130.4 (3)	N3—C6—N2	116.7 (3)
N4—N3—C6	118.3 (3)	N5—C6—N2	118.2 (3)
N3—N4—C7	116.8 (3)	N5—C6—N3	125.1 (3)
N6—N5—C6	117.2 (3)	N6—C7—N4	124.4 (3)
N5—N6—C7	117.6 (2)	N7—C7—N4	119.8 (3)
N8—N7—H7	120.0	N7—C7—N6	115.8 (3)
C7—N7—H7	120.0	N8—C8—H8	119.2
C7—N7—N8	120.0 (3)	N8—C8—C9	121.6 (3)
C8—N8—N7	115.6 (3)	C9—C8—H8	119.2
C12—O1—H1	109.5	C10—C9—C8	119.6 (3)
H1A—C1—H1B	109.5	C10—C9—C14	117.9 (3)
H1A—C1—H1C	109.5	C14—C9—C8	122.5 (3)
H1B—C1—H1C	109.5	C9—C10—H10	119.2
C2—C1—H1A	109.5	C11—C10—C9	121.7 (3)
C2—C1—H1B	109.5	C11—C10—H10	119.2
C2—C1—H1C	109.5	C10—C11—H11	120.1
N1—C2—C1	120.4 (3)	C10—C11—C12	119.7 (3)
N1—C2—C3	111.5 (3)	C12—C11—H11	120.1
C3—C2—C1	128.0 (3)	O1—C12—C11	115.9 (3)
C2—C3—H3	126.8	O1—C12—C13	124.1 (3)
C4—C3—C2	106.5 (3)	C13—C12—C11	120.0 (3)
C4—C3—H3	126.8	C12—C13—H13	120.1
N2—C4—C5	125.1 (3)	C14—C13—C12	119.8 (3)
C3—C4—N2	105.3 (3)	C14—C13—H13	120.1
C3—C4—C5	129.6 (3)	C9—C14—H14	119.6
C4—C5—H5A	109.5	C13—C14—C9	120.9 (3)
C4—C5—H5B	109.5	C13—C14—H14	119.6
C4—C5—H5C	109.5

N1—N2—C4—C3	0.1 (4)	C1—C2—C3—C4	179.2 (3)
N1—N2—C4—C5	179.8 (3)	C2—N1—N2—C4	−0.2 (3)
N1—N2—C6—N3	−6.3 (4)	C2—N1—N2—C6	179.6 (3)
N1—N2—C6—N5	176.0 (3)	C2—C3—C4—N2	0.0 (4)
N1—C2—C3—C4	−0.1 (4)	C2—C3—C4—C5	−179.7 (3)
N2—N1—C2—C1	−179.2 (3)	C4—N2—C6—N3	173.4 (3)
N2—N1—C2—C3	0.2 (4)	C4—N2—C6—N5	−4.3 (5)
N3—N4—C7—N6	6.7 (5)	C6—N2—C4—C3	−179.6 (3)
N3—N4—C7—N7	−175.5 (3)	C6—N2—C4—C5	0.1 (5)
N4—N3—C6—N2	176.0 (3)	C6—N3—N4—C7	0.4 (4)
N4—N3—C6—N5	−6.4 (5)	C6—N5—N6—C7	1.8 (4)
N5—N6—C7—N4	−7.9 (4)	C7—N7—N8—C8	178.9 (3)
N5—N6—C7—N7	174.2 (3)	C8—C9—C10—C11	−179.8 (3)
N6—N5—C6—N2	−177.3 (3)	C8—C9—C14—C13	179.8 (3)
N6—N5—C6—N3	5.2 (4)	C9—C10—C11—C12	−0.3 (5)
N7—N8—C8—C9	−180.0 (3)	C10—C9—C14—C13	0.2 (5)
N8—N7—C7—N4	1.4 (4)	C10—C11—C12—O1	−179.6 (3)
N8—N7—C7—N6	179.5 (3)	C10—C11—C12—C13	0.7 (5)
N8—C8—C9—C10	−178.4 (3)	C11—C12—C13—C14	−0.7 (5)
N8—C8—C9—C14	1.9 (5)	C12—C13—C14—C9	0.2 (5)
O1—C12—C13—C14	179.6 (3)	C14—C9—C10—C11	−0.1 (5)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···N1ⁱ	0.82	2.45	2.895 (4)	115
O1—H1···N3ⁱ	0.82	2.28	3.090 (4)	172
N7—H7···N6ⁱⁱ	0.86	2.21	3.060 (4)	169
C5—H5A···N5	0.96	2.11	2.863 (4)	134
C13—H13···N4ⁱ	0.93	2.60	3.490 (4)	161

Symmetry codes: (i) −x, −y, −z+1; (ii) −x+2, −y, −z+2.

Kinetic parameters of the exothermic decomposition reaction for DAHBTz and DPHM at various heating rates top

Compound	DAHBTz		DPHM
Heating rates β (K min^-1)	T_e (K)	T_p (K)	T_e (K)	T_p (K)
5	468.78	469.76	496.76	497.70
10	474.07	476.02	502.81	504.15
15	478.74	480.25	507.20	507.87
20	480.29	481.85	510.17	511.36
25	483.06	485.01	511.44	513.89
30	–	–	513.08	515.42
Kissinger method
E_k (kJ mol^-1)	194.14		204.05
log (A_k s^-1)	19.54		19.34
Linear correlation coefficient (r_k)	0.998		0.999
Ozawa method
E_o (kJ mol^-1)	192.18		202.05
Linear correlation coefficient (r_o)	0.998		0.999
¯E (kJ mol^-1)	193.16		203.05
T_SADT = T_e0 (K)	463.15		490.11
T_p0 (K)	463.95		491.37
T_b (K)	473.66		501.73

Notes: T_e is the onset temperature in the DSC curve; T_p is the maximum peak temperature; T_SADT is the self-accelerating decomposition temperature; T_b is the critical temperature of thermal explosion; E is the apparent activation energy; A is the pre-exponential constant; r is the linear correlation coefficient, with subscript `k' indicating data obtained by the Kissinger method and subscript `o' indicating data obtained by the Ozawa method.

Nitrogen equivalents of different detonation products top

Detonation product	N₂	H₂O	CO	CO₂	C	H₂
Nitrogen equivalent index	1	0.54	0.78	1.35	0.15	0.29

Detonation velocity (D) and detonation pressure (P) of DPHM and DAHBTz top

Compound	ΣN	D (m s^-1)	P (GPa)
DPHM	2.70	6348.85	15.75
DAHBTz	2.76	6332.21	15.33

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Synthesis, crystal structure and thermal properties of an unsymmetrical 1,2,4,5-tetra­zine energetic derivative

Supporting information

Synthesis, crystal structure and thermal properties of an unsymmetrical 1,2,4,5-tetrazine energetic derivative