Acta Cryst. (2009). E65, o1275 [ doi:10.1107/S1600536809017036 ]
In the six-membered ring of the low-temperature crystal structure of benzofurazan 1-oxide, C6H4N2O2, the two C atoms adjacent to the N atoms are linked by a delocalized aromatic bond [1.402 (2) Å]; each is connected to its neighbour by a longer, more localized, bond [1.420 (2), 1.430 (2) Å]. However, the next two bonds in the ring approximate double bonds [1.357 (2), 1.366 (2) Å]. As such, the six-membered ring is better described as a cyclohexadiene system, in contrast to the description in the room-temperature structure reported by Britton & Olson (1979) [Acta Cryst. B35, 3076-3078].
The compound was synthesized according to a reported procedure (Terrian et al., 1992; Wolthius, 1979). Crystals were grown with THF as solvent.
The carbon-bound H-atoms were restrained to C—H 0.95±0.01 Å; their temperature factors were freely refined.
Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: publCIF (Westrip, 2009).
![[Figure 1]](./tk2443fig1thm.gif)
| Fig. 1. The molecular structure of the title compound. Displacement ellipsoids are drawn at the 70% probability level, and hydrogen atoms are drawn as spheres of arbitrary radius. |
| C6H4N2O2 | Z = 2 |
| Mr = 136.11 | F000 = 140 |
| Triclinic, P1 | Dx = 1.550 Mg m−3 |
| Hall symbol: -P 1 | Mo Kα radiation λ = 0.71073 Å |
| a = 6.6751 (2) Å | Cell parameters from 1320 reflections |
| b = 7.3256 (2) Å | θ = 3.2–28.3º |
| c = 7.6842 (2) Å | µ = 0.12 mm−1 |
| α = 100.710 (2)º | T = 100 K |
| β = 114.265 (2)º | Irregular block, yellow-orange |
| γ = 111.747 (2)º | 0.30 × 0.25 × 0.10 mm |
| V = 291.71 (1) Å3 |
| Bruker SMART APEX diffractometer | 1110 reflections with I > 2σ(I) |
| Radiation source: fine-focus sealed tube | Rint = 0.012 |
| Monochromator: graphite | θmax = 27.5º |
| T = 100 K | θmin = 3.2º |
| ω scans | h = −7→8 |
| Absorption correction: None | k = −9→9 |
| 1952 measured reflections | l = −9→9 |
| 1276 independent reflections |
| Refinement on F2 | Secondary atom site location: difference Fourier map |
| Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
| R[F2 > 2σ(F2)] = 0.035 | All H-atom parameters refined |
| wR(F2) = 0.110 | w = 1/[σ2(Fo2) + (0.0685P)2 + 0.0855P] where P = (Fo2 + 2Fc2)/3 |
| S = 1.03 | (Δ/σ)max = 0.001 |
| 1276 reflections | Δρmax = 0.33 e Å−3 |
| 108 parameters | Δρmin = −0.21 e Å−3 |
| 4 restraints | Extinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
| Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.03 (1) |
| C6H4N2O2 | γ = 111.747 (2)º |
| Mr = 136.11 | V = 291.71 (1) Å3 |
| Triclinic, P1 | Z = 2 |
| a = 6.6751 (2) Å | Mo Kα |
| b = 7.3256 (2) Å | µ = 0.12 mm−1 |
| c = 7.6842 (2) Å | T = 100 K |
| α = 100.710 (2)º | 0.30 × 0.25 × 0.10 mm |
| β = 114.265 (2)º |
| Bruker SMART APEX diffractometer | 1276 independent reflections |
| Absorption correction: None | 1110 reflections with I > 2σ(I) |
| 1952 measured reflections | Rint = 0.012 |
| R[F2 > 2σ(F2)] = 0.035 | 4 restraints |
| wR(F2) = 0.110 | All H-atom parameters refined |
| S = 1.03 | Δρmax = 0.33 e Å−3 |
| 1276 reflections | Δρmin = −0.21 e Å−3 |
| 108 parameters |
| x | y | z | Uiso*/Ueq | ||
| O1 | 0.1183 (2) | 0.2141 (2) | −0.0082 (1) | 0.0274 (3) | |
| O2 | 0.5178 (2) | 0.2611 (2) | 0.1146 (1) | 0.0271 (3) | |
| N1 | 0.3061 (2) | 0.2329 (2) | 0.1385 (2) | 0.0211 (3) | |
| N2 | 0.7112 (2) | 0.2839 (2) | 0.2955 (2) | 0.0257 (3) | |
| C1 | 0.6232 (2) | 0.2701 (2) | 0.4219 (2) | 0.0188 (3) | |
| C2 | 0.7496 (3) | 0.2863 (2) | 0.6308 (2) | 0.0202 (3) | |
| C3 | 0.6182 (3) | 0.2669 (2) | 0.7284 (2) | 0.0207 (3) | |
| C4 | 0.3643 (3) | 0.2321 (2) | 0.6312 (2) | 0.0209 (3) | |
| C5 | 0.2382 (3) | 0.2174 (2) | 0.4325 (2) | 0.0199 (3) | |
| C6 | 0.3750 (2) | 0.2377 (2) | 0.3296 (2) | 0.0181 (3) | |
| H2 | 0.919 (2) | 0.310 (3) | 0.693 (3) | 0.030 (4)* | |
| H3 | 0.701 (3) | 0.278 (3) | 0.867 (2) | 0.037 (5)* | |
| H4 | 0.281 (3) | 0.221 (3) | 0.706 (2) | 0.027 (4)* | |
| H5 | 0.072 (2) | 0.197 (3) | 0.369 (2) | 0.031 (4)* |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| O1 | 0.0242 (5) | 0.0333 (6) | 0.0172 (5) | 0.0139 (4) | 0.0039 (4) | 0.0130 (4) |
| O2 | 0.0270 (6) | 0.0398 (6) | 0.0190 (5) | 0.0172 (5) | 0.0137 (4) | 0.0157 (4) |
| N1 | 0.0213 (6) | 0.0237 (6) | 0.0158 (5) | 0.0105 (5) | 0.0077 (5) | 0.0098 (4) |
| N2 | 0.0237 (6) | 0.0361 (7) | 0.0202 (6) | 0.0155 (5) | 0.0120 (5) | 0.0144 (5) |
| C1 | 0.0198 (6) | 0.0199 (6) | 0.0171 (6) | 0.0096 (5) | 0.0095 (5) | 0.0090 (5) |
| C2 | 0.0187 (6) | 0.0231 (6) | 0.0175 (6) | 0.0109 (5) | 0.0072 (5) | 0.0103 (5) |
| C3 | 0.0240 (7) | 0.0215 (6) | 0.0147 (6) | 0.0109 (5) | 0.0083 (5) | 0.0093 (5) |
| C4 | 0.0246 (7) | 0.0228 (6) | 0.0192 (6) | 0.0120 (5) | 0.0137 (6) | 0.0102 (5) |
| C5 | 0.0188 (6) | 0.0213 (6) | 0.0200 (6) | 0.0104 (5) | 0.0096 (5) | 0.0096 (5) |
| C6 | 0.0200 (6) | 0.0175 (6) | 0.0136 (5) | 0.0086 (5) | 0.0066 (5) | 0.0073 (4) |
| O1—N1 | 1.230 (1) | C3—C4 | 1.436 (2) |
| O2—N2 | 1.381 (1) | C4—C5 | 1.366 (2) |
| O2—N1 | 1.443 (2) | C5—C6 | 1.420 (2) |
| N1—C6 | 1.336 (2) | C2—H2 | 0.956 (9) |
| N2—C1 | 1.327 (2) | C3—H3 | 0.948 (9) |
| C1—C6 | 1.409 (2) | C4—H4 | 0.946 (9) |
| C1—C2 | 1.430 (2) | C5—H5 | 0.947 (9) |
| C2—C3 | 1.357 (2) | ||
| N2—O2—N1 | 109.4 (1) | N1—C6—C1 | 106.9 (1) |
| O1—N1—C6 | 136.0 (1) | N1—C6—C5 | 129.7 (1) |
| O1—N1—O2 | 117.7 (1) | C1—C6—C5 | 123.5 (1) |
| C6—N1—O2 | 106.3 (1) | C3—C2—H2 | 124 (1) |
| C1—N2—O2 | 105.0 (1) | C1—C2—H2 | 119 (1) |
| N2—C1—C6 | 112.5 (1) | C2—C3—H3 | 117 (1) |
| N2—C1—C2 | 128.0 (1) | C4—C3—H3 | 120 (1) |
| C6—C1—C2 | 119.5 (1) | C5—C4—H4 | 118 (1) |
| C3—C2—C1 | 116.8 (1) | C3—C4—H4 | 120 (1) |
| C2—C3—C4 | 122.9 (1) | C4—C5—H5 | 122 (1) |
| C5—C4—C3 | 121.9 (1) | C6—C5—H5 | 122 (1) |
| C4—C5—C6 | 115.4 (1) | ||
| N2—O2—N1—O1 | 178.7 (1) | O1—N1—C6—C1 | −178.3 (1) |
| N2—O2—N1—C6 | −0.4 (1) | O2—N1—C6—C1 | 0.6 (1) |
| N1—O2—N2—C1 | 0.1 (1) | O1—N1—C6—C5 | 1.2 (2) |
| O2—N2—C1—C6 | 0.3 (2) | O2—N1—C6—C5 | −179.9 (1) |
| O2—N2—C1—C2 | −179.1 (1) | N2—C1—C6—N1 | −0.5 (2) |
| N2—C1—C2—C3 | 179.9 (1) | C2—C1—C6—N1 | 178.9 (1) |
| C6—C1—C2—C3 | 0.6 (2) | N2—C1—C6—C5 | 179.9 (1) |
| C1—C2—C3—C4 | −0.1 (2) | C2—C1—C6—C5 | −0.7 (2) |
| C2—C3—C4—C5 | −0.4 (2) | C4—C5—C6—N1 | −179.2 (1) |
| C3—C4—C5—C6 | 0.3 (2) | C4—C5—C6—C1 | 0.2 (2) |
| O1—N1 | 1.230 (1) | C1—C2 | 1.430 (2) |
| O2—N2 | 1.381 (1) | C2—C3 | 1.357 (2) |
| O2—N1 | 1.443 (2) | C3—C4 | 1.436 (2) |
| N1—C6 | 1.336 (2) | C4—C5 | 1.366 (2) |
| N2—C1 | 1.327 (2) | C5—C6 | 1.420 (2) |
| C1—C6 | 1.409 (2) |
Ammon, H. L. & Bhattacharjee, S. K. (1982). Acta Cryst. B38, 2498–2502.
Barbour, L. J. (2001). J. Supramol. Chem. 1, 189–191.
Bird, C. W. (1993). Tetrahedron, 49, 8441–8448.
Britton, D. & Olson, J. M. (1979). Acta Cryst. B35, 3076–3078.
Bruker (2008). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.
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Westrip, S. P. (2009). publCIF. In preparation.
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Researchers have used the published structure of benzofurazan 1-oxide (Britton & Olson, 1979) in, for example, studies on packing (Ammon & Bhattacharjee, 1982; Ojala et al., 1999; Ramm et al., 1991), influence of N-oxide formation on heteroaromaticity (Bird, 1993), and reactivity and biology (Cerecetto & González, 2007). Bond dimensions from geometry-optimization calculations (Friedrichsen, 1995; Ponder et al.,1994; Rauhut, 1996) have also been compared with values taken from the solid-state structure.
The present low-temperature structure (Fig. 1 & Table 1) reveals features quite distinct from those disclosed in the original, room-temperature, analysis (Britton & Olson, 1979). In the six-membered ring, the two carbon atoms adjacent to the nitrogen atoms are linked by a delocalized aromatic bond [1.402 (2) Å]; each is connected to its neighbor by a longer, more localized, bond [1.420 (2), 1.430 (2) Å]. However, the next two bonds in the ring approximate double-bonds [1.357 (2), 1.366 (2) Å]. As such, the six-membered ring is better described as a cyclohexadiene system.