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The hexanitro­cubane structure, C8H2N6O12, reported herein, is one of the last in the series of nitro­cubanes, ranging from mono- to octa­nitro­cubane. In this mol­ecule, the H atoms participate in short hydrogen-bonding contacts to the nitro O atoms in adjoining mol­ecules [2.50 (1) Å], thus linking mol­ecules into a two-dimensional sheet in the bc plane. In addition, the O...O contacts in hexanitro­cubane are shorter than van der Waals contact distances. The shortest of these [2.766 (3) Å] involve the O atoms of one of the attached nitro groups. These contacts involve mol­ecules in an extended two-dimensional sheet parallel to the ab plane.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536802013739/ac6009sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536802013739/ac6009Isup2.hkl
Contains datablock I

CCDC reference: 197462

Key indicators

  • Single-crystal X-ray study
  • T = 295 K
  • Mean [sigma](C-C) = 0.002 Å
  • R factor = 0.046
  • wR factor = 0.136
  • Data-to-parameter ratio = 10.5

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


Yellow Alert Alert Level C:
PLAT_320 Alert C Check Hybridisation of C3 in main residue ? PLAT_320 Alert C Check Hybridisation of C4 in main residue ? PLAT_320 Alert C Check Hybridisation of C5 in main residue ? PLAT_320 Alert C Check Hybridisation of C6 in main residue ? PLAT_320 Alert C Check Hybridisation of C7 in main residue ? PLAT_320 Alert C Check Hybridisation of C8 in main residue ?
1 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
6 Alert Level C = Please check

Comment top

Nitrocubanes have long been sought after as powerful, shock-insensitive, high-density explosives (Eaton, 1992). In these compounds are combined the energy associated with the highly strained cubane skeleton (Eaton, 1992) with that associated with polynitrated compounds. One of the more interesting stories in organic synthesis in recent years has been the long (ca 20 years) development of methods (Eaton at al., 2000) to make octanitrocubane (Zhang et al., 2000), the `holy grail' of the energetic materials community. Theoretical predictions (Alster et al., 1981) had indicated that this compound would have one of the highest densities observed in compounds containing only C, H, N and O. In this search, the structures of 1,4-dinitro (Eaton et al., 1984), 1,3,5-trinitro- (Eaton et al., 1993), 1,3,5,7-tetranitro- (Eaton et al., 1993), 1,2,3,5,7-pentanitro- (Lukin et al., 1997), 1,2,3,4,5,6,8-heptanitro- (Zhang et al., 2000), and 1,2,3,4,5,6,7,8-octanitrocubane (Zhang et al., 2000) have been reported. However, to date the structure of the simplest member of this series, nitrocubane, is only now being reported (Butcher & Gilardi, 2002).

The structure of 1,2,3,4,5,7-hexanitrocubane, (I), is reported herein; previously the structure of its acetonitrile solvate was reported (Lukin et al., 1997). Pure hexanitrocubane crystallizes in the orthorhombic space group Pnma with four molecules in the unit cell, thus the molecule has crystallographically imposed mirror symmetry, which passes through atoms C3, N3, O3A, O3B, C5, N5, O5A, O5B, C6, H6, C8, and H8. Positions C4A and C7A, generated by the mirror plane, correspond to positions C2 and C1 in the conventional cubane numbering scheme. In hexanitrocubane, the C—C bond lengths average 1.565 (6) Å, which is somewhat longer than the average found in all cubane structures, but well within the normal range (Butcher et al., 1995). The nitro O atomd attached to N7 are disordered over two positions, with occupancies of 0.600 (4) and 0.400 (4), which is not unusual for such moieties. As the number of nitro substituents increase, H atoms attached to the cubane skeleton become increasingly acidic (Lukin et al., 1997), and thus participate in stronger hydrogen-bonding interactions than is commonly observed for hydrocarbon H atoms. In this instance, both H6 and H8 participate in short hydrogen-bonding contacts to O7AB in adjoining molecules (2.501 Å), thus linking molecules into a two-dimensional sheet in the bc plane, as shown in Fig. 1. In addition, just as is the case in pentanitrocubane (Lukin et al., 1997), heptanitrocubane (Zhang et al., 2000), and octanitrocubane (Zhang et al., 2000), several O···O contacts in hexanitrocubane are shorter than the van der Waals contact distance of 3.04 Å (Rowland & Taylor, 1996). The shortest of these, 2.766 Å, involve the O atoms of the nitro group attached to C4. In hexanitrocubane, the nitro groups attached to C4 (and C4A which is related to C4 by the crystallographic mirror plane) are the only nitro groups that are ortho to three other nitro groups. These contacts are between the molecules that lie in an extended two-dimensional sheet parallel to the ab plane, as shown in Fig. 2.

Density is of critical importance to the performance of an explosive. The overall packing in hexanitrocubane described above leads to a density of 1.931 Mg m−3 at 294 K. While this is less than that observed for pentanitrocubane (1.959 Mg m−3; Lukin et al., 1997), heptanitrocubane (2.028 Mg m−3; Zhang et al., 2000), and octanitrocubane (1.979 Mg m−3; Zhang et al., 2000), this is still an impressive value for a compound containing only C, H, N, and O, and is much higher than the value previously observed for its acetonitrile solvate (1.676 Mg m−3; Lukin et al., 1997). The metrical parameters found for this unsolvated structure of hexanitrocubane are very similar to those found for the acetonitrile solvate (Lukin et al., 1997).

Experimental top

The preparation of hexanitrobenzene has been reported previously (Lukin et al., 1997). Solvent-free crytals were grown by slow evaporation from a mixed HNO3/H2SO4 solution at 313 K.

Refinement top

All H atoms were initially located in a difference Fourier map and refined isotropically. The nitro O atoms attached to N7 are disordered over two positions, with occupancies of 0.600 (4) and 0.400 (4), as is commonly found for such moieties.

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SMART; data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. Displacement ellipsoid plot (50% probability level) of the title molecule, showing the atomic labeling scheme.
[Figure 2] Fig. 2. The molecules of (I) linking into a two-dimensional sheet in the bc plane through short hydrogen-bonding contacts to C7 in adjoining molecules.
[Figure 3] Fig. 3. Short O···O contacts from the C4 nitro group linking up molecules in an extended two-dimensional sheet parallel to the ab plane.
(I) top
Crystal data top
C8H2N6O12Dx = 1.931 Mg m3
Mr = 374.16Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, PnmaCell parameters from 4545 reflections
a = 13.936 (2) Åθ = 2.8–28.3°
b = 10.8870 (19) ŵ = 0.19 mm1
c = 8.4833 (14) ÅT = 295 K
V = 1287.1 (4) Å3Plate, orange
Z = 40.74 × 0.29 × 0.11 mm
F(000) = 752
Data collection top
Bruker P4/CCD
diffractometer
1655 independent reflections
Radiation source: fine-focus sealed tube1202 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.026
ω scansθmax = 28.3°, θmin = 2.8°
Absorption correction: multi-scan
(Bruker, 2001)
h = 1818
Tmin = 0.819, Tmax = 0.962k = 1414
9511 measured reflectionsl = 119
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.046Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.136All H-atom parameters refined
S = 1.03 w = 1/[σ2(Fo2) + (0.0747P)2 + 0.3718P]
where P = (Fo2 + 2Fc2)/3
1655 reflections(Δ/σ)max < 0.001
157 parametersΔρmax = 0.35 e Å3
0 restraintsΔρmin = 0.24 e Å3
Crystal data top
C8H2N6O12V = 1287.1 (4) Å3
Mr = 374.16Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 13.936 (2) ŵ = 0.19 mm1
b = 10.8870 (19) ÅT = 295 K
c = 8.4833 (14) Å0.74 × 0.29 × 0.11 mm
Data collection top
Bruker P4/CCD
diffractometer
1655 independent reflections
Absorption correction: multi-scan
(Bruker, 2001)
1202 reflections with I > 2σ(I)
Tmin = 0.819, Tmax = 0.962Rint = 0.026
9511 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0460 restraints
wR(F2) = 0.136All H-atom parameters refined
S = 1.03Δρmax = 0.35 e Å3
1655 reflectionsΔρmin = 0.24 e Å3
157 parameters
Special details top

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 (Å2) top
xyzUiso*/UeqOcc. (<1)
C30.33820 (19)0.25001.0939 (3)0.0356 (5)
N30.3347 (2)0.25001.2689 (3)0.0518 (7)
O3A0.4094 (2)0.25001.3397 (3)0.0794 (8)
O3B0.2542 (2)0.25001.3251 (3)0.0773 (8)
C40.29000 (12)0.14906 (14)0.98930 (18)0.0323 (4)
N40.24031 (12)0.03958 (13)1.05379 (18)0.0427 (4)
O4A0.27462 (14)0.00370 (15)1.17313 (19)0.0716 (5)
O4B0.17065 (13)0.00225 (15)0.9865 (2)0.0725 (5)
C50.24530 (16)0.25000.8802 (3)0.0315 (5)
N50.14369 (16)0.25000.8305 (3)0.0452 (6)
O5A0.12710 (16)0.25000.6895 (3)0.0625 (6)
O5B0.08567 (15)0.25000.9385 (3)0.0760 (8)
C60.33648 (18)0.25000.7732 (3)0.0325 (5)
H60.336 (2)0.25000.658 (3)0.045 (7)*
C70.38139 (12)0.14914 (14)0.88278 (18)0.0329 (4)
N70.43102 (11)0.03600 (15)0.8312 (2)0.0438 (4)
O7AA0.4809 (6)0.0462 (8)0.7150 (7)0.0646 (16)0.60
O7AB0.4202 (5)0.0520 (6)0.9158 (7)0.0768 (17)0.60
O7BA0.5027 (10)0.0394 (12)0.7631 (17)0.121 (5)0.40
O7BB0.3923 (6)0.0640 (8)0.8610 (9)0.0605 (18)0.40
C80.42940 (19)0.25000.9894 (3)0.0363 (5)
H80.4926 (19)0.25001.021 (3)0.042 (8)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C30.0498 (14)0.0238 (11)0.0332 (11)0.0000.0025 (10)0.000
N30.092 (2)0.0281 (11)0.0351 (11)0.0000.0040 (14)0.000
O3A0.117 (2)0.0733 (17)0.0480 (11)0.0000.0317 (14)0.000
O3B0.111 (2)0.0656 (16)0.0549 (13)0.0000.0323 (14)0.000
C40.0395 (9)0.0229 (8)0.0345 (7)0.0000 (6)0.0022 (7)0.0006 (6)
N40.0555 (10)0.0282 (7)0.0446 (8)0.0059 (7)0.0095 (7)0.0016 (6)
O4A0.1071 (14)0.0452 (9)0.0623 (9)0.0093 (9)0.0083 (9)0.0233 (8)
O4B0.0769 (12)0.0621 (10)0.0784 (11)0.0336 (9)0.0040 (9)0.0073 (9)
C50.0329 (12)0.0247 (11)0.0369 (11)0.0000.0004 (10)0.000
N50.0376 (12)0.0329 (11)0.0650 (14)0.0000.0057 (11)0.000
O5A0.0580 (13)0.0601 (14)0.0694 (14)0.0000.0271 (11)0.000
O5B0.0426 (12)0.0911 (19)0.0943 (18)0.0000.0200 (13)0.000
C60.0373 (13)0.0277 (11)0.0326 (10)0.0000.0003 (10)0.000
C70.0333 (8)0.0266 (8)0.0388 (8)0.0023 (6)0.0005 (7)0.0020 (6)
N70.0370 (9)0.0352 (8)0.0593 (10)0.0051 (7)0.0041 (7)0.0106 (7)
O7AA0.061 (4)0.061 (3)0.0717 (18)0.012 (3)0.029 (2)0.0052 (17)
O7AB0.110 (5)0.038 (2)0.083 (3)0.030 (3)0.005 (2)0.011 (2)
O7BA0.053 (5)0.060 (6)0.251 (15)0.012 (4)0.060 (8)0.062 (8)
O7BB0.069 (4)0.030 (2)0.082 (5)0.003 (3)0.021 (3)0.001 (3)
C80.0380 (14)0.0276 (11)0.0433 (12)0.0000.0080 (11)0.000
Geometric parameters (Å, º) top
C3—N31.486 (3)N5—O5A1.218 (3)
C3—C81.550 (4)N5—O5B1.222 (3)
C3—C41.564 (2)C6—C7i1.569 (2)
C3—C4i1.564 (2)C6—C71.569 (2)
N3—O3A1.202 (4)C6—H60.98 (3)
N3—O3B1.218 (4)C7—N71.479 (2)
C4—N41.483 (2)C7—C81.572 (2)
C4—C71.562 (2)N7—O7BA1.155 (14)
C4—C51.566 (2)N7—O7AB1.206 (7)
N4—O4B1.197 (2)N7—O7AA1.211 (7)
N4—O4A1.215 (2)N7—O7BB1.241 (9)
C5—N51.478 (3)C8—C7i1.572 (2)
C5—C61.562 (3)C8—H80.92 (3)
C5—C4i1.566 (2)
N3—C3—C8126.8 (2)C5—C6—C788.85 (13)
N3—C3—C4123.56 (14)C7i—C6—C788.82 (16)
C8—C3—C491.57 (14)C5—C6—H6125.3 (17)
N3—C3—C4i123.56 (14)C7i—C6—H6126.5 (9)
C8—C3—C4i91.57 (14)C7—C6—H6126.5 (9)
C4—C3—C4i89.27 (17)N7—C7—C4123.51 (14)
O3A—N3—O3B127.0 (3)N7—C7—C6126.46 (14)
O3A—N3—C3118.1 (3)C4—C7—C691.03 (13)
O3B—N3—C3114.9 (3)N7—C7—C8123.57 (14)
N4—C4—C7126.49 (13)C4—C7—C890.84 (14)
N4—C4—C3123.77 (14)C6—C7—C891.25 (12)
C7—C4—C388.72 (14)O7BA—N7—O7AB115.6 (8)
N4—C4—C5126.60 (15)O7BA—N7—O7AA25.0 (9)
C7—C4—C588.97 (13)O7AB—N7—O7AA129.0 (5)
C3—C4—C590.75 (12)O7BA—N7—O7BB120.4 (8)
O4B—N4—O4A125.80 (17)O7AB—N7—O7BB29.3 (4)
O4B—N4—C4118.39 (16)O7AA—N7—O7BB119.7 (6)
O4A—N4—C4115.81 (16)O7BA—N7—C7121.7 (7)
N5—C5—C6127.9 (2)O7AB—N7—C7115.3 (4)
N5—C5—C4i123.35 (13)O7AA—N7—C7115.6 (4)
C6—C5—C4i91.14 (13)O7BB—N7—C7117.9 (5)
N5—C5—C4123.35 (13)C3—C8—C788.86 (15)
C6—C5—C491.14 (13)C3—C8—C7i88.86 (15)
C4i—C5—C489.14 (16)C7—C8—C7i88.63 (17)
O5A—N5—O5B127.6 (3)C3—C8—H8127.9 (17)
O5A—N5—C5117.5 (2)C7—C8—H8125.2 (9)
O5B—N5—C5114.9 (2)C7i—C8—H8125.2 (9)
C5—C6—C7i88.85 (13)
C8—C3—N3—O3A0.000 (1)C4—C5—C6—C70.16 (11)
C4—C3—N3—O3A122.53 (19)N4—C4—C7—N70.2 (3)
C4i—C3—N3—O3A122.53 (19)C3—C4—C7—N7132.63 (15)
C8—C3—N3—O3B180.0C5—C4—C7—N7136.60 (15)
C4—C3—N3—O3B57.47 (19)N4—C4—C7—C6136.61 (16)
C4i—C3—N3—O3B57.47 (19)C3—C4—C7—C690.93 (12)
N3—C3—C4—N43.4 (3)C5—C4—C7—C60.16 (11)
C8—C3—C4—N4134.15 (16)N4—C4—C7—C8132.13 (16)
C4i—C3—C4—N4134.30 (13)C3—C4—C7—C80.33 (12)
N3—C3—C4—C7137.9 (2)C5—C4—C7—C891.10 (12)
C8—C3—C4—C70.33 (12)C5—C6—C7—N7134.57 (16)
C4i—C3—C4—C791.22 (14)C7i—C6—C7—N7136.56 (13)
N3—C3—C4—C5133.2 (2)C5—C6—C7—C40.16 (12)
C8—C3—C4—C589.29 (14)C7i—C6—C7—C489.04 (13)
C4i—C3—C4—C52.26 (17)C5—C6—C7—C890.70 (14)
C7—C4—N4—O4B98.4 (2)C7i—C6—C7—C81.83 (17)
C3—C4—N4—O4B144.17 (19)C4—C7—N7—O7BA173.7 (8)
C5—C4—N4—O4B23.1 (3)C6—C7—N7—O7BA65.2 (9)
C7—C4—N4—O4A82.3 (2)C8—C7—N7—O7BA56.3 (9)
C3—C4—N4—O4A35.2 (2)C4—C7—N7—O7AB25.1 (4)
C5—C4—N4—O4A156.29 (17)C6—C7—N7—O7AB146.2 (3)
N4—C4—C5—N51.9 (3)C8—C7—N7—O7AB92.3 (4)
C7—C4—C5—N5138.61 (18)C4—C7—N7—O7AA158.6 (4)
C3—C4—C5—N5132.68 (19)C6—C7—N7—O7AA37.6 (5)
N4—C4—C5—C6136.53 (16)C8—C7—N7—O7AA84.0 (5)
C7—C4—C5—C60.16 (12)C4—C7—N7—O7BB7.6 (4)
C3—C4—C5—C688.87 (14)C6—C7—N7—O7BB113.5 (4)
N4—C4—C5—C4i132.34 (12)C8—C7—N7—O7BB125.0 (4)
C7—C4—C5—C4i90.97 (13)N3—C3—C8—C7135.67 (8)
C3—C4—C5—C4i2.26 (17)C4—C3—C8—C70.33 (12)
C6—C5—N5—O5A0.0C4i—C3—C8—C788.98 (12)
C4i—C5—N5—O5A122.84 (16)N3—C3—C8—C7i135.67 (8)
C4—C5—N5—O5A122.84 (16)C4—C3—C8—C7i88.98 (12)
C6—C5—N5—O5B180.0C4i—C3—C8—C7i0.33 (12)
C4i—C5—N5—O5B57.16 (16)N7—C7—C8—C3132.58 (16)
C4—C5—N5—O5B57.16 (16)C4—C7—C8—C30.33 (12)
N5—C5—C6—C7i135.58 (8)C6—C7—C8—C390.72 (14)
C4i—C5—C6—C7i0.16 (11)N7—C7—C8—C7i138.53 (13)
C4—C5—C6—C7i89.00 (11)C4—C7—C8—C7i89.22 (14)
N5—C5—C6—C7135.58 (8)C6—C7—C8—C7i1.83 (17)
C4i—C5—C6—C789.00 (11)
Symmetry code: (i) x, y+1/2, z.

Experimental details

Crystal data
Chemical formulaC8H2N6O12
Mr374.16
Crystal system, space groupOrthorhombic, Pnma
Temperature (K)295
a, b, c (Å)13.936 (2), 10.8870 (19), 8.4833 (14)
V3)1287.1 (4)
Z4
Radiation typeMo Kα
µ (mm1)0.19
Crystal size (mm)0.74 × 0.29 × 0.11
Data collection
DiffractometerBruker P4/CCD
diffractometer
Absorption correctionMulti-scan
(Bruker, 2001)
Tmin, Tmax0.819, 0.962
No. of measured, independent and
observed [I > 2σ(I)] reflections
9511, 1655, 1202
Rint0.026
(sin θ/λ)max1)0.667
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.046, 0.136, 1.03
No. of reflections1655
No. of parameters157
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.35, 0.24

Computer programs: SMART (Bruker, 2001), SMART, SAINT (Bruker, 2001), SHELXTL (Sheldrick, 1997), SHELXTL.

 

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