3-Nitro-1-nitromethyl-1H-1,2,4-triazole

The title compound, C₃H₃N₅O₄, consists of three planar fragments twisted in relation to each other, namely a triazole ring, a nitro­methyl­ene group and a nitro group. Molecular conformation analysis shows that the first stage of thermal decomposition is a breakage of the H₂C-NO₂ bond. There are essential conformational differences in the mol­ecule in comparison with semi-empirical calculations.

S1. Comment

Nitro derivatives of 1,2,4-triazole are of interest as highly energetic compounds (Pevzner, 1997). X-ray structure investigation of the compounds is important not only for providing unambiguous confirmation of their molecular structure; since one of the basic characteristics of explosives is their density, it is necessary to know their structure parameters to reveal factors that have an influence on crystal density (Stein, 1981), with the ultimate aim of enabling a computer search of hypothetical high density highly energetic compounds and their subsequent synthesis (Coburn et al., 1986). No less important is that knowledge of the structure parameters of a highly energetic molecule allow the prediction of its reaction ability, in particular its thermal stability (Manelis et al., 1996). Accordingly, the structure of the title compound, (I), was investigated using single-crystal X-ray techniques. \sch

The molecule of (I) (Fig.1) consists of three bonded planar fragments, namely a 1,2,4-triazole ring, a nitromethylene group and a nitro group (H atoms are omitted from the consideration). The triazole cycle is practically planar [r.m.s. deviation 0.0014 (8), maximum deviation 0.002 (8) Å]. The interatomic distances within the cycle are not equal, ranging from 1.304 (2) to 1.355 (2) Å. The nitro group bonded with the triazole ring is located at 17.8 (2)° with respect to the ring plane. The nitromethylene group is strictly planar and is located nearly orthogonal [83.25 (6)°] to the triazole ring, while the torsion angle O3—N8—C7—N1 is 2.8 (2)°. The C—NO₂ bond lengths are not equal [1.450 (2) and 1.509 (2) Å]: the greater value relates to the bond in the nitroalkyl fragment of the molecule. On the whole, bond lengths and angles in (I) are close to the corresponding values in other nitro derivatives of 1,2,4-triazole (Closset et al., 1975; Starova et al., 1977; Nikitina et al., 1982).

The structure of (I) has been investigated theoretically by semi-empirical MNDO, AM1 and PM3 methods (please define; Stepanov et al., 2000). In contrast to the experimental data, these calculations show that the location of the nitro group orthogonal to the triazole ring is more preferable. This disagreement might be due to the incorrect evaluation of the resonance effect between the triazole cycle and the nitro group. According to? the semi-empirical calculations, the torsion angle O3—N8—C7—N1 is in the range 44–60°, depending on the calculation method. Calculated C—NO₂ bond lengths are somewhat overestimated, with values of 1.482–1.512 and 1.553–1.571 Å for nitro groups bonded to the triazole cycle and the methylene fragment, respectively. However, the X-ray results confirm earlier inference concerning the preference of nitro-group breakage in the nitromethylene part of (I) during thermal decomposition (Stepanov et al., 2000).

In conclusion, we note that the density of (I) (1.76 Mg m⁻³) exceeds the density of the brutto-formula isomer 1-methyl-3,5-dinitro-1,2,4-triazole (1.63 Mg m⁻³; Starova et al., 1977). This fact leads to the expectation of an increase in the value of the detonation velocity by 400–500 m s⁻¹ for (I) in comparison with the latter compound. It would be expected that the high density of a crystal composed of organic molecules is associated with short intermolecular distances, but all intermolecular atom-atom distances exceed the corresponding sums of ordinary van der Waals radii in the crystal of (I).

S2. Experimental

Compound (I) (Stepanov et al., 2000) was obtained by double recrystallization from water (m.p. 453 K with decomposition). Single crystals were obtained by evaporation of a saturated alcohol (which?) solution.

Computing details

Data collection: KM-4 Software (Kuma, 1991); cell refinement: KM-4 Software; data reduction: KM-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL (Sheldrick, 1995); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. The molecule of (I) showing the atom-numbering scheme and with 50% probability displacement ellipsoids. H atoms are drawn as small spheres of arbitrary radii.

3-Nitro-1-nitromethyl-1H-1,2,4-triazole

Crystal data

C3H3N5O4	F(000) = 352
Mr = 173.10	Dx = 1.758 Mg m^−3
Monoclinic, P21/c	Cu Kα radiation, λ = 1.54051 Å
a = 6.6305 (4) Å	Cell parameters from 25 reflections
b = 9.2888 (3) Å	θ = 22–30°
c = 10.9828 (6) Å	µ = 1.44 mm^−1
β = 104.837 (5)°	T = 293 K
V = 653.87 (6) Å^3	Plate, colourless
Z = 4	0.35 × 0.30 × 0.25 mm

Data collection

Kuma KM-4 four-circle diffractometer	Rint = 0.019
Radiation source: fine-focus sealed tube	θmax = 70.0°, θmin = 6.3°
Graphite monochromator	h = −8→7
profile data from ω/2θ scans	k = −11→11
2493 measured reflections	l = 0→13
1195 independent reflections	2 standard reflections every 50 reflections
1015 reflections with I > 2σ(I)	intensity decay: none

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.032	All H-atom parameters refined
wR(F^2) = 0.087	Calculated w = 1/[σ^2(Fo^2) + (0.0492P)^2 + 0.1343P] where P = (Fo^2 + 2Fc^2)/3
S = 1.03	(Δ/σ)max < 0.001
1195 reflections	Δρmax = 0.18 e Å^−3
122 parameters	Δρmin = −0.17 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0170 (15)

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
N2	0.01891 (17)	0.18566 (12)	0.05048 (11)	0.0333 (3)
N1	0.14659 (17)	0.15240 (11)	0.16441 (11)	0.0315 (3)
N4	−0.01845 (19)	0.34469 (13)	0.19974 (12)	0.0432 (3)
O3	0.48807 (18)	0.22243 (13)	0.10386 (13)	0.0612 (4)
C3	−0.0729 (2)	0.29980 (14)	0.08001 (13)	0.0322 (3)
N8	0.48470 (18)	0.09794 (13)	0.13424 (11)	0.0391 (3)
N6	−0.22771 (18)	0.37542 (13)	−0.01595 (12)	0.0408 (3)
O1	−0.3053 (2)	0.31141 (14)	−0.11321 (12)	0.0633 (4)
C7	0.2991 (2)	0.04162 (15)	0.17534 (15)	0.0361 (3)
O4	0.62109 (18)	0.01055 (14)	0.13497 (12)	0.0610 (4)
O2	−0.2692 (2)	0.49800 (12)	0.00697 (13)	0.0647 (4)
C5	0.1219 (2)	0.24805 (16)	0.25091 (15)	0.0410 (4)
H1	0.352 (2)	0.0150 (17)	0.2643 (17)	0.040 (4)*
H2	0.249 (2)	−0.0362 (18)	0.1221 (17)	0.044 (4)*
H3	0.198 (3)	0.2389 (18)	0.3351 (19)	0.054 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N2	0.0333 (6)	0.0325 (6)	0.0332 (6)	−0.0001 (4)	0.0071 (5)	−0.0012 (4)
N1	0.0298 (6)	0.0317 (5)	0.0323 (6)	−0.0020 (4)	0.0068 (5)	−0.0002 (4)
N4	0.0420 (7)	0.0447 (7)	0.0432 (7)	0.0022 (5)	0.0113 (6)	−0.0113 (5)
O3	0.0474 (7)	0.0528 (7)	0.0893 (10)	0.0006 (5)	0.0284 (6)	0.0266 (6)
C3	0.0302 (6)	0.0301 (6)	0.0374 (7)	−0.0034 (5)	0.0107 (6)	−0.0007 (5)
N8	0.0339 (6)	0.0460 (7)	0.0365 (7)	0.0057 (5)	0.0075 (5)	0.0034 (5)
N6	0.0392 (6)	0.0372 (6)	0.0474 (8)	0.0030 (5)	0.0137 (6)	0.0055 (5)
O1	0.0709 (8)	0.0650 (8)	0.0438 (7)	0.0172 (6)	−0.0039 (6)	0.0025 (6)
C7	0.0356 (7)	0.0302 (6)	0.0417 (8)	0.0001 (5)	0.0083 (6)	0.0029 (6)
O4	0.0487 (7)	0.0706 (8)	0.0662 (8)	0.0238 (6)	0.0191 (6)	0.0033 (6)
O2	0.0678 (8)	0.0385 (6)	0.0856 (10)	0.0178 (5)	0.0156 (7)	0.0051 (6)
C5	0.0411 (8)	0.0471 (8)	0.0344 (8)	−0.0003 (6)	0.0088 (7)	−0.0074 (6)

Geometric parameters (Å, º)

N2—C3	1.3043 (17)	N8—O4	1.2138 (15)
N2—N1	1.3547 (17)	N8—C7	1.5088 (18)
N1—C5	1.3410 (18)	N6—O2	1.2129 (17)
N1—C7	1.4261 (17)	N6—O1	1.2157 (17)
N4—C5	1.311 (2)	C7—H1	0.981 (18)
N4—C3	1.3380 (18)	C7—H2	0.936 (17)
O3—N8	1.2053 (16)	C5—H3	0.94 (2)
C3—N6	1.4503 (19)
C3—N2—N1	100.18 (10)	O2—N6—C3	117.38 (13)
C5—N1—N2	110.03 (11)	O1—N6—C3	117.60 (12)
C5—N1—C7	129.12 (13)	N1—C7—N8	109.86 (11)
N2—N1—C7	120.28 (11)	N1—C7—H1	109.3 (9)
C5—N4—C3	101.02 (11)	N8—C7—H1	106.0 (9)
N2—C3—N4	118.16 (12)	N1—C7—H2	111.8 (10)
N2—C3—N6	120.10 (12)	N8—C7—H2	105.7 (10)
N4—C3—N6	121.73 (12)	H1—C7—H2	114.0 (14)
O3—N8—O4	125.23 (13)	N4—C5—N1	110.60 (14)
O3—N8—C7	119.33 (11)	N4—C5—H3	128.9 (11)
O4—N8—C7	115.44 (12)	N1—C5—H3	120.5 (11)
O2—N6—O1	125.03 (14)
C3—N2—N1—C5	−0.34 (14)	N4—C3—N6—O1	−162.62 (13)
C3—N2—N1—C7	−172.45 (11)	C5—N1—C7—N8	−91.94 (16)
N1—N2—C3—N4	0.39 (15)	N2—N1—C7—N8	78.49 (14)
N1—N2—C3—N6	179.72 (11)	O3—N8—C7—N1	2.83 (19)
C5—N4—C3—N2	−0.28 (16)	O4—N8—C7—N1	−177.18 (13)
C5—N4—C3—N6	−179.59 (12)	C3—N4—C5—N1	0.03 (15)
N2—C3—N6—O2	−161.68 (13)	N2—N1—C5—N4	0.21 (16)
N4—C3—N6—O2	17.63 (19)	C7—N1—C5—N4	171.42 (13)
N2—C3—N6—O1	18.08 (19)