2,6-Di­amino-3,5-di­nitro­pyrazine

The title compound, C₄H₄N₆O₄, crystallizes in the monoclinic space group P2₁/c, and is an energetic compound containing only C, H, N and O atoms, with a density of 1.812 Mg m^-3. Thus, it is a very stable di­aza analog of 1,3,5-tri­amino-2,4,6-tri­nitro­benzene (TATB). Like TATB, it packs in planar graphite-like layers in the ab plane, with mol­ecules held together by intermolecular hydrogen bonding. Both compounds decompose at temperatures above 573 K and are insoluble in most common solvents. Crystals of the title compound are usually twinned (twins related by a 180° rotation about a*) and the crystal analyzed had a minor twin component.

Key indicators

• Single-crystal X-ray study
• T = 294 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.064
• wR factor = 0.187
• Data-to-parameter ratio = 17.5

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level A:



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           25.50
         From the CIF: _reflns_number_total               2526
         TEST2: Reflns within _diffrn_reflns_theta_max
         Count of symmetry unique reflns         1364
         Completeness (_total/calc)            185.19%
          Alert A: > 15% excess reflns - sys abs data present?


 1 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 0 Alert Level C = Please check

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S1. Comment

The title compound, 2,6-diamino-3,5-dinitro-1,4-pyrazine (ANPZ), (I), is a very stable insensitive energetic material with a high density of 1.812 Mg m^-3. Thus, it is a very stable diaza analog of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB).

In ANPZ, every H atom is either involved in intramolecular hydrogen-bonding interactions to a neighboring O atom or intermolecular hydrogen-bonding interactions with O atoms from adjoining molecules. This results in a packing scheme in which the molecules are strongly linked in two-dimensional planar graphite-like layers in the ab plane which stack along the c direction. Both ANPZ and TATB decompose at temperatures above 573 K and are insoluble in most common solvents. Crystals of the title compound are usually twinned (twins related by a 180° rotation about a*) and the crystal analyzed had a minor twin component. It is related to other similar energetic compounds, such as TATB (TATB: Cady & Larson, 1965; Kolb & Rizzo, 1979) and 2,6-diamino-3,5-dinitropyrazine-1-oxide (ANPZO: Gilardi & Butcher, 2001) which have a similar system of extensive intra- and intermolecular hydrogen-bonding interactions, resulting in a sheet-like packing system, high densities (1.937 and 1.919 Mg m^-3, respectively), and relative insensitivity. One of the potentially useful features of ANPZ is its insensitivity. Sensitivity is often tested via the drop height method, i.e. the height of the drop of a steel ball required to detonate the compound, with large values reflecting insensitivity. In such testing, in common with TATB, the benchmark compound as regards insensitivity, ANPZ has values which are so large they cannot be accurately measured, while ANPZO has a value of 117 cm (Pagoria et al., 1998). Thus, while the density of ANPZ is less than that of ANPZO, it is much less sensitive. Thus ANPZ is much safer than other commonly used energetic compounds such as trinitrotoluene (80 cm) and HMX (32 cm). Fig. 1 shows the structure and labeling scheme for the title compound. Hydrogen-bonding metrical parameters are given in Table 1.

S2. Experimental

Crystals of the title compound were supplied by Dr Philip Pagoria, Energetic Materials Laboratory, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA. Crystal and reflection data were obtained using standard procedures (Butcher et al.., 1995).

S3. Refinement

Crystals of the title compound were all found to be twinned by a 180° rotation about a*. This leads to almost coincidence of l = 2n (n > 0) reflections, complete separation of l = 2n + 1 reflections, and complete overlap of l = 0 reflections with reflections originating from the minor twin. It was found that the indices of coincident or almost coincident reflections were related by: h_w = h_s + (l_s/2), k_w = -k_s and l_w = -l_s, where w and s stand for weak and strong. This was handled by using the appropriate matrix with the TWIN instruction in SHELXTL (Sheldrick, 1997) and a scale factor for the minor component. After refinement the fraction of the minor component was found to be only 0.06655.

Computing details

Data collection: XSCANS (Siemens, 1994); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 1994); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. View of 2,6-diamino-3,5-dinitro-1,4-pyrazine showing the labeling of all non-H atoms. Displacement ellipsoids are at the 20% level; H atoms are drawn as small circles of arbitrary radii.
	Fig. 2. Packing diagram of 2,6-diamino-3,5-dinitro-1,4-pyrazine. Hydrogen bonds are indicated by dashed lines.
	Fig. 3. Packing diagram for 2,6-diamino-3,5-dinitro-1,4-pyrazine showing the parallel layers in the bc plane, viewed down the a axis.

2,6-diamino-3,5-dinitro-1,4-pyrazine

Crystal data

C4H4N6O4	F(000) = 408
Mr = 200.13	Dx = 1.812 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 9.0136 (18) Å	Cell parameters from 49 reflections
b = 12.960 (6) Å	θ = 2.3–19.9°
c = 6.3936 (13) Å	µ = 0.16 mm^−1
β = 100.77 (3)°	T = 294 K
V = 733.7 (4) Å^3	Plate, yellow
Z = 4	0.35 × 0.28 × 0.12 mm

Data collection

Bruker P4 diffractometer	1715 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 25.5°, θmin = 2.3°
2θ/ω scans	h = −10→10
Absorption correction: integration (Wuensch & Prewitt, 1965)	k = −15→15
Tmin = 0.943, Tmax = 0.981	l = −7→7
2526 measured reflections	3 standard reflections every 97 reflections
2526 independent reflections	intensity decay: 1%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.064	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.187	All H-atom parameters refined
S = 1.04	w = 1/[σ^2(Fo^2) + (0.1032P)^2 + 0.2079P] where P = (Fo^2 + 2Fc^2)/3
2526 reflections	(Δ/σ)max = 0.004
144 parameters	Δρmax = 0.30 e Å^−3
0 restraints	Δρmin = −0.24 e Å^−3

Special details

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N1	0.7327 (2)	−0.24279 (14)	0.2573 (4)	0.0367 (6)
N2	0.4980 (3)	−0.30646 (18)	0.2548 (4)	0.0429 (6)
C2	0.5874 (3)	−0.22459 (18)	0.2559 (4)	0.0331 (6)
O3B	0.3445 (2)	−0.00087 (14)	0.2488 (4)	0.0582 (7)
O3A	0.2907 (2)	−0.16227 (15)	0.2565 (5)	0.0641 (8)
C3	0.5366 (2)	−0.11883 (18)	0.2551 (4)	0.0316 (6)
N3	0.3822 (2)	−0.09156 (16)	0.2531 (4)	0.0396 (6)
N4	0.6293 (2)	−0.04153 (15)	0.2522 (4)	0.0341 (5)
O5B	0.8104 (2)	0.11422 (15)	0.2378 (5)	0.0691 (8)
C5	0.7718 (3)	−0.06090 (18)	0.2528 (5)	0.0348 (6)
N5	0.8674 (3)	0.02843 (16)	0.2493 (4)	0.0446 (6)
O5A	1.0021 (2)	0.01563 (16)	0.2560 (5)	0.0688 (8)
C6	0.8293 (3)	−0.16459 (19)	0.2571 (4)	0.0347 (6)
N6	0.9713 (3)	−0.1890 (2)	0.2588 (5)	0.0520 (8)
H1	0.539 (3)	−0.375 (2)	0.252 (4)	0.039 (7)*
H2	0.400 (4)	−0.295 (3)	0.253 (6)	0.069 (11)*
H3	1.037 (3)	−0.146 (2)	0.261 (5)	0.041 (8)*
H4	0.997 (4)	−0.247 (3)	0.262 (6)	0.058 (11)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0348 (11)	0.0225 (10)	0.0532 (15)	0.0036 (8)	0.0092 (10)	−0.0004 (10)
N2	0.0423 (13)	0.0201 (11)	0.0675 (18)	−0.0037 (9)	0.0130 (11)	0.0001 (10)
C2	0.0339 (13)	0.0228 (12)	0.0421 (16)	0.0000 (9)	0.0055 (10)	0.0005 (11)
O3B	0.0397 (11)	0.0262 (11)	0.112 (2)	0.0070 (7)	0.0228 (11)	0.0009 (11)
O3A	0.0321 (10)	0.0323 (11)	0.129 (2)	−0.0055 (8)	0.0191 (11)	0.0058 (13)
C3	0.0275 (13)	0.0206 (11)	0.0469 (16)	−0.0022 (9)	0.0073 (11)	0.0006 (11)
N3	0.0320 (11)	0.0250 (11)	0.0622 (17)	−0.0020 (8)	0.0099 (10)	0.0017 (10)
N4	0.0318 (11)	0.0225 (10)	0.0484 (14)	−0.0007 (8)	0.0082 (9)	0.0000 (9)
O5B	0.0437 (12)	0.0219 (10)	0.143 (3)	−0.0024 (8)	0.0213 (13)	0.0031 (12)
C5	0.0290 (13)	0.0238 (12)	0.0523 (18)	−0.0010 (9)	0.0098 (11)	0.0003 (12)
N5	0.0321 (12)	0.0289 (12)	0.0739 (18)	−0.0038 (9)	0.0124 (11)	0.0003 (11)
O5A	0.0310 (11)	0.0405 (12)	0.137 (2)	−0.0045 (8)	0.0201 (12)	0.0039 (13)
C6	0.0321 (13)	0.0271 (12)	0.0452 (16)	0.0017 (9)	0.0084 (10)	0.0004 (11)
N6	0.0337 (14)	0.0321 (14)	0.091 (2)	0.0039 (11)	0.0139 (13)	−0.0004 (13)

Geometric parameters (Å, º)

N1—C2	1.328 (3)	C3—N3	1.434 (3)
N1—C6	1.337 (3)	N4—C5	1.308 (3)
N2—C2	1.331 (3)	O5B—N5	1.221 (3)
C2—C3	1.445 (3)	C5—C6	1.439 (3)
O3B—N3	1.222 (3)	C5—N5	1.445 (3)
O3A—N3	1.235 (3)	N5—O5A	1.219 (3)
C3—N4	1.307 (3)	C6—N6	1.316 (3)
C2—N1—C6	120.5 (2)	C3—N4—C5	118.9 (2)
N1—C2—N2	116.9 (2)	N4—C5—C6	122.0 (2)
N1—C2—C3	118.7 (2)	N4—C5—N5	115.7 (2)
N2—C2—C3	124.4 (2)	C6—C5—N5	122.3 (2)
N4—C3—N3	115.7 (2)	O5A—N5—O5B	122.1 (2)
N4—C3—C2	121.6 (2)	O5A—N5—C5	118.9 (2)
N3—C3—C2	122.7 (2)	O5B—N5—C5	119.0 (2)
O3B—N3—O3A	122.0 (2)	N6—C6—N1	116.8 (2)
O3B—N3—C3	120.2 (2)	N6—C6—C5	124.8 (2)
O3A—N3—C3	117.8 (2)	N1—C6—C5	118.4 (2)
C6—N1—C2—N2	179.5 (3)	C3—N4—C5—C6	−0.2 (4)
C6—N1—C2—C3	−0.3 (4)	C3—N4—C5—N5	180.0 (3)
N1—C2—C3—N4	1.1 (4)	N4—C5—N5—O5A	177.9 (3)
N2—C2—C3—N4	−178.7 (3)	C6—C5—N5—O5A	−2.0 (4)
N1—C2—C3—N3	179.9 (3)	N4—C5—N5—O5B	−2.8 (4)
N2—C2—C3—N3	0.1 (4)	C6—C5—N5—O5B	177.3 (3)
N4—C3—N3—O3B	0.1 (4)	C2—N1—C6—N6	179.9 (3)
C2—C3—N3—O3B	−178.7 (3)	C2—N1—C6—C5	−0.7 (4)
N4—C3—N3—O3A	−179.8 (3)	N4—C5—C6—N6	−179.7 (3)
C2—C3—N3—O3A	1.4 (4)	N5—C5—C6—N6	0.2 (5)
N3—C3—N4—C5	−179.7 (2)	N4—C5—C6—N1	1.0 (4)
C2—C3—N4—C5	−0.9 (4)	N5—C5—C6—N1	−179.2 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H1···O3B^i	0.96 (3)	1.94 (3)	2.894 (4)	170 (2)
N2—H1···N4^i	0.96 (3)	2.64 (3)	3.253 (3)	122.0 (19)
N2—H2···O3A	0.89 (4)	1.98 (4)	2.644 (3)	130 (3)
N2—H2···O5B^i	0.89 (4)	2.25 (3)	2.973 (3)	138 (3)
N6—H3···O5A	0.81 (3)	2.11 (3)	2.667 (4)	125 (3)
N6—H3···O3A^ii	0.81 (3)	2.30 (3)	2.903 (3)	131 (3)
N6—H4···O5B^iii	0.79 (4)	2.50 (4)	3.219 (3)	153 (3)

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