4,10-Dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX): a nitramine with an exceptionally high density

The title compound (systematic name: 4,10-di­nitro-2,6,8,12-tetraoxa-4,10-di­aza­tetra­cyclo­[5.5.0.0^3,11.0^5,9]­do­decane), C₆H₆N₄O₈, exhibits the highest density among known N-nitramines, due to its close-packed crystal structure. It may be regarded as consisting of a distorted hexagonal close-packed lattice formed by the isowurtzitane cages, with the nitro groups occupying the free space between the cages.

S1. Comment

4,10-Dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane, TEX, hereinafter (I), is an insensitive highly energetic material which was first described by Ramakrishnan and coworkers in 1990 (Ramakrishnan et al., 1990). It displays the highest density ever recorded for a nitramine and therefore a very high detonation velocity (7470 m s^-1), according to both Jacob et al. (2000) and Li et al. (2001), while its sensitivity towards shock, impact or friction is extremely low, as mentioned by Vagenknecht (2000) and Zeman (1999). These and other features make (I) a highly interesting model compound for the investigation of explosion processes. \sch

A recently published X-ray structure of (I) (Yu et al., 1996) does not provide any information about the crystal lattice (such as lattice constants, space group, atom positions in the unit cell etc.). Since the density of an explosive compound is closely related to its explosion properties, we were prompted to investigate closely the crystal lattice of (I) in order to find an explanation for its extraordinarily high density. The molecule shows a cage structure composed of three C₂ units, which are linked by four O atoms and two N atoms which bear a nitro group (Fig. 1).

The seven-membered rings put a strain on the cage and thus increase the energy content of the molecule. A part of the explosive power of (I) is derived from this cage strain. The extraordinarily high density of (I) may be explained by the compactness of the molecule, which can be described, except for the nitro groups, as nearly spherical (Fig. 1). Atoms N11 and N31 are coordinated, as expected, in a planar manner [sums of angles both 359.9 (4)°]. There is a significant deviation from planarity in the coordination of atoms N1 and N3, with angle sums of 343.2 (3)° for N1 and 351.2 (4)° for N3. Atoms C1—C4 deviate only slightly from the planes defined by the respective nitro groups. The N—N bond length appears in both cases (N1—N11 and N3—N31) to be shorter (1.40–1.41 Å) than a single N—N bond (1.48 Å), but much longer than a double bond (1.20 Å). The C3—C4 and C1—C2 bond distances [both 1.56 (2) Å] are slightly shorter than that of C5—C6 [1.58 (1) Å]. A possible reason for this difference is the fact that the C1—C2 and C3—C4 bonds connect a five-membered and a seven-membered ring and are thus less strained than the C5—C6 bond, which connects two seven-membered rings. The Pitzer strain destabilizes the seven-membered rings to a higher degree than the five-membered ones.

Compound (I) crystallizes in a structure that is remarkably similar to a distorted hexagonal close packing of spheres. The crystal lattice of (I) contains molecules in two different orientations (Fig. 2). Within the structure, the shortest distances between molecule cages are O1···O4ⁱ [2.8773 (15) Å], O111···O111ⁱⁱ [2.999 (2) Å] and C6···O1ⁱ [2.9974 (18) Å], all of which are significantly shorter than the sum of Van der Waals radii (3.0 Å for O···O and 3.2 Å for C···O; Holleman et al., 1995) [symmetry codes: (i) -x, 1 - y, 1 - z; (ii) -x, 1 - y, -z].

Relatively short distances are observed for H2···O4 [2.49 (2) Å], H3···O211 [2.394 (16) Å] and H4···O111 [2.49 (2) Å], with C—H···O angles of 174.9 (14)° for C2—H2···O4, 140.5 (14)° for C3—H3···O211 and 133.4 (14)° for C4—H4···O111, (Table 2 and Fig. 2). However, due to the comparatively long H···O distances and C—H···O angles deviating significantly from linearity, we may assume that the contacts cannot be regarded as bonding.

Table 2. C—H···O hydrogen-bonding and contact geometry (Å, °).

S2. Experimental

The title compound was synthesized as described by Ramakrishnan et al. (1990). Crystallization by slow evaporation from a saturated solution of (I) in acetone afforded colourless crystals suitable for X-ray analysis.

Computing details

Data collection: EXPOSE in IPDS (Stoe & Cie, 1997); cell refinement: CELL in IPDS; data reduction: INTEGRATE in IPDS; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandeburg, 1996); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the molecule of (I) showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. Close O—H contacts in the crystal structure of (I), forming a three-dimensional network.

4,10-Dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane

Crystal data

C6H6N4O8	Z = 2
Mr = 262.15	F(000) = 268
Triclinic, P1	Dx = 2.008 (1) Mg m^−3
Hall symbol: -P 1	Melting point: decomp. > 473 K
a = 6.8360 (12) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.6404 (14) Å	Cell parameters from 3304 reflections
c = 8.7765 (16) Å	θ = 2.4–27.9°
α = 82.37 (2)°	µ = 0.19 mm^−1
β = 75.05 (2)°	T = 200 K
γ = 79.46 (2)°	Prismatic, colourless
V = 433.64 (14) Å^3	0.27 × 0.27 × 0.20 mm

Data collection

Stoe IPDS diffractometer	1911 independent reflections
Radiation source: fine-focus sealed tube	1555 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
ϕ scans	θmax = 28.1°, θmin = 2.4°
Absorption correction: numerical (X-RED; Stoe & Cie, 1997)	h = −8→9
Tmin = 0.958, Tmax = 0.971	k = −10→10
3698 measured reflections	l = −11→10

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)] = 0.034	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.099	All H-atom parameters refined
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0684P)^2 + 0.0238P] where P = (Fo^2 + 2Fc^2)/3
1911 reflections	(Δ/σ)max < 0.001
187 parameters	Δρmax = 0.25 e Å^−3
0 restraints	Δρmin = −0.25 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	0.33969 (18)	0.44852 (15)	0.16131 (14)	0.0147 (3)
N11	0.25635 (19)	0.61331 (16)	0.09075 (16)	0.0190 (3)
O111	0.16876 (19)	0.60570 (16)	−0.01222 (16)	0.0287 (3)
O211	0.2887 (2)	0.74885 (15)	0.13161 (17)	0.0334 (3)
C1	0.4157 (2)	0.46362 (18)	0.29802 (17)	0.0160 (3)
H1	0.492 (3)	0.561 (2)	0.277 (2)	0.016 (4)*
C2	0.5403 (2)	0.28002 (18)	0.34348 (17)	0.0159 (3)
H2	0.677 (3)	0.291 (2)	0.341 (2)	0.015 (4)*
N3	0.53746 (18)	0.15391 (15)	0.23494 (15)	0.0156 (3)
N31	0.69513 (19)	0.00807 (16)	0.21436 (15)	0.0176 (3)
O131	0.84518 (17)	0.01483 (15)	0.26158 (16)	0.0276 (3)
O231	0.67333 (19)	−0.11302 (14)	0.14468 (14)	0.0258 (3)
C3	0.3375 (2)	0.12532 (18)	0.22548 (17)	0.0152 (3)
H3	0.354 (3)	0.042 (2)	0.149 (2)	0.012 (4)*
C4	0.2130 (2)	0.30791 (17)	0.17962 (17)	0.0143 (3)
H4	0.169 (3)	0.310 (2)	0.082 (2)	0.010 (4)*
O1	0.25545 (16)	0.49642 (13)	0.43588 (12)	0.0175 (2)
O2	0.43333 (16)	0.23317 (14)	0.50157 (12)	0.0179 (2)
O3	0.21710 (15)	0.06749 (13)	0.37520 (12)	0.0169 (2)
O4	0.03965 (15)	0.33142 (13)	0.30945 (12)	0.0161 (2)
C5	0.2302 (2)	0.32432 (18)	0.51536 (17)	0.0169 (3)
H5	0.166 (3)	0.336 (2)	0.625 (2)	0.017 (4)*
C6	0.1002 (2)	0.22496 (18)	0.44005 (17)	0.0162 (3)
H6	−0.018 (3)	0.193 (2)	0.516 (2)	0.013 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0162 (6)	0.0117 (5)	0.0171 (6)	−0.0031 (4)	−0.0057 (5)	0.0003 (4)
N11	0.0173 (6)	0.0155 (6)	0.0219 (6)	−0.0023 (4)	−0.0029 (5)	0.0024 (5)
O111	0.0274 (6)	0.0277 (6)	0.0353 (7)	−0.0085 (5)	−0.0187 (6)	0.0100 (5)
O211	0.0486 (8)	0.0136 (5)	0.0407 (7)	−0.0049 (5)	−0.0160 (6)	−0.0010 (5)
C1	0.0165 (6)	0.0156 (6)	0.0166 (7)	−0.0048 (5)	−0.0029 (6)	−0.0027 (5)
C2	0.0152 (7)	0.0170 (6)	0.0169 (7)	−0.0035 (5)	−0.0051 (6)	−0.0026 (5)
N3	0.0134 (6)	0.0144 (5)	0.0194 (6)	0.0004 (4)	−0.0047 (5)	−0.0046 (4)
N31	0.0162 (6)	0.0168 (6)	0.0170 (6)	0.0018 (4)	−0.0026 (5)	−0.0006 (4)
O131	0.0184 (5)	0.0276 (6)	0.0378 (7)	0.0016 (4)	−0.0121 (5)	−0.0023 (5)
O231	0.0304 (6)	0.0206 (5)	0.0261 (6)	0.0061 (4)	−0.0088 (5)	−0.0111 (4)
C3	0.0157 (6)	0.0145 (6)	0.0167 (7)	−0.0029 (5)	−0.0047 (6)	−0.0033 (5)
C4	0.0135 (6)	0.0143 (6)	0.0164 (7)	−0.0040 (5)	−0.0042 (6)	−0.0025 (5)
O1	0.0208 (5)	0.0140 (5)	0.0164 (5)	−0.0030 (4)	−0.0009 (4)	−0.0041 (4)
O2	0.0171 (5)	0.0204 (5)	0.0159 (5)	−0.0010 (4)	−0.0051 (4)	−0.0013 (4)
O3	0.0171 (5)	0.0125 (4)	0.0205 (5)	−0.0037 (4)	−0.0036 (4)	0.0001 (4)
O4	0.0126 (5)	0.0160 (5)	0.0188 (5)	−0.0019 (4)	−0.0037 (4)	0.0007 (4)
C5	0.0183 (7)	0.0155 (6)	0.0148 (7)	−0.0010 (5)	−0.0017 (6)	−0.0008 (5)
C6	0.0140 (6)	0.0146 (6)	0.0182 (7)	−0.0017 (5)	−0.0022 (6)	0.0009 (5)

Geometric parameters (Å, º)

N1—N11	1.4162 (16)	N31—O231	1.2247 (18)
N1—C1	1.450 (2)	C3—O3	1.4214 (17)
N1—C4	1.4672 (18)	C3—C4	1.5574 (19)
N11—O211	1.2139 (19)	C3—H3	0.956 (18)
N11—O111	1.218 (2)	C4—O4	1.4196 (17)
C1—O1	1.4222 (17)	C4—H4	0.975 (19)
C1—C2	1.5628 (19)	O1—C5	1.4222 (16)
C1—H1	0.958 (19)	O2—C5	1.4174 (17)
C2—O2	1.4243 (17)	O3—C6	1.4162 (17)
C2—N3	1.4480 (19)	O4—C6	1.4215 (17)
C2—H2	0.949 (19)	C5—C6	1.577 (2)
N3—N31	1.3962 (16)	C5—H5	0.96 (2)
N3—C3	1.4476 (19)	C6—H6	0.950 (18)
N31—O131	1.2128 (19)
N11—N1—C1	114.58 (11)	N3—C3—C4	108.98 (11)
N11—N1—C4	113.14 (12)	O3—C3—H3	111.4 (10)
C1—N1—C4	115.51 (11)	N3—C3—H3	109.4 (11)
O211—N11—O111	125.88 (13)	C4—C3—H3	111.2 (11)
O211—N11—N1	117.19 (14)	O4—C4—N1	111.36 (11)
O111—N11—N1	116.79 (12)	O4—C4—C3	104.26 (11)
O1—C1—N1	112.64 (12)	N1—C4—C3	108.86 (11)
O1—C1—C2	104.09 (11)	O4—C4—H4	110.0 (10)
N1—C1—C2	109.16 (11)	N1—C4—H4	109.1 (10)
O1—C1—H1	107.2 (11)	C3—C4—H4	113.3 (10)
N1—C1—H1	109.7 (11)	C5—O1—C1	104.89 (10)
C2—C1—H1	114.0 (11)	C5—O2—C2	105.36 (11)
O2—C2—N3	112.57 (11)	C6—O3—C3	105.63 (10)
O2—C2—C1	103.42 (11)	C4—O4—C6	105.37 (10)
N3—C2—C1	108.68 (12)	O2—C5—O1	104.12 (11)
O2—C2—H2	110.0 (11)	O2—C5—C6	112.09 (11)
N3—C2—H2	110.4 (11)	O1—C5—C6	112.07 (12)
C1—C2—H2	111.5 (10)	O2—C5—H5	108.9 (12)
N31—N3—C3	117.11 (12)	O1—C5—H5	109.1 (11)
N31—N3—C2	117.67 (12)	C6—C5—H5	110.3 (12)
C3—N3—C2	116.42 (11)	O3—C6—O4	104.40 (11)
O131—N31—O231	125.47 (13)	O3—C6—C5	111.58 (11)
O131—N31—N3	117.40 (13)	O4—C6—C5	111.20 (11)
O231—N31—N3	117.07 (13)	O3—C6—H6	108.1 (10)
O3—C3—N3	112.19 (12)	O4—C6—H6	109.6 (11)
O3—C3—C4	103.64 (10)	C5—C6—H6	111.6 (11)
C1—N1—N11—O211	12.66 (18)	N11—N1—C4—C3	168.67 (11)
C4—N1—N11—O211	147.93 (13)	C1—N1—C4—C3	−56.49 (15)
C1—N1—N11—O111	−171.48 (12)	O3—C3—C4—O4	0.65 (14)
C4—N1—N11—O111	−36.20 (17)	N3—C3—C4—O4	−118.99 (12)
N11—N1—C1—O1	75.85 (14)	O3—C3—C4—N1	119.59 (12)
C4—N1—C1—O1	−58.34 (15)	N3—C3—C4—N1	−0.05 (15)
N11—N1—C1—C2	−169.05 (10)	N1—C1—O1—C5	93.25 (13)
C4—N1—C1—C2	56.76 (14)	C2—C1—O1—C5	−24.87 (14)
O1—C1—C2—O2	0.09 (14)	N3—C2—O2—C5	−92.23 (13)
N1—C1—C2—O2	−120.41 (12)	C1—C2—O2—C5	24.88 (14)
O1—C1—C2—N3	119.90 (12)	N3—C3—O3—C6	92.86 (13)
N1—C1—C2—N3	−0.59 (14)	C4—C3—O3—C6	−24.56 (14)
O2—C2—N3—N31	−89.44 (14)	N1—C4—O4—C6	−93.86 (13)
C1—C2—N3—N31	156.62 (11)	C3—C4—O4—C6	23.36 (14)
O2—C2—N3—C3	57.19 (16)	C2—O2—C5—O1	−41.71 (14)
C1—C2—N3—C3	−56.76 (15)	C2—O2—C5—C6	79.64 (13)
C3—N3—N31—O131	−161.29 (12)	C1—O1—C5—O2	41.58 (14)
C2—N3—N31—O131	−14.90 (18)	C1—O1—C5—C6	−79.78 (13)
C3—N3—N31—O231	21.39 (17)	C3—O3—C6—O4	40.32 (13)
C2—N3—N31—O231	167.78 (12)	C3—O3—C6—C5	−79.89 (13)
N31—N3—C3—O3	89.65 (14)	C4—O4—C6—O3	−39.73 (13)
C2—N3—C3—O3	−57.16 (15)	C4—O4—C6—C5	80.73 (13)
N31—N3—C3—C4	−156.16 (11)	O2—C5—C6—O3	−0.26 (15)
C2—N3—C3—C4	57.03 (15)	O1—C5—C6—O3	116.40 (12)
N11—N1—C4—O4	−76.93 (15)	O2—C5—C6—O4	−116.39 (12)
C1—N1—C4—O4	57.91 (15)	O1—C5—C6—O4	0.27 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2···O4^i	0.95 (2)	2.49 (2)	3.439 (2)	174.9 (14)
C3—H3···O211^ii	0.956 (16)	2.394 (16)	3.192 (2)	140.5 (14)
C4—H4···O231^iii	0.976 (18)	2.546 (16)	3.238 (2)	127.9 (14)
C4—H4···O111^iv	0.976 (18)	2.49 (2)	3.240 (2)	133.4 (14)
C6—H6···O3^v	0.953 (19)	2.559 (18)	3.365 (2)	142.7 (12)

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