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The two isomeric compounds 4-amino-
ONN-azoxybenzene [or 1-(4-aminophenyl)-2-phenyldiazene 2-oxide],
i.e. the α isomer, and 4-amino-
NNO-azoxybenzene [or 2-(4-aminophenyl)-1-phenyldiazene 2-oxide],
i.e. the β isomer, both C
12H
11N
3O, crystallized from a polar solvent in orthorhombic space groups, and their crystal and molecular structures have been determined using X-ray diffraction. There are no significant differences in the bond lengths and valence angles in the two isomers, in comparison with their monoclinic polymorphs. However, the conformations of the molecules are different due to rotation along the Ar—N bonds. In the α isomer, the benzene rings are twisted by 31.5 (2) and 14.4 (2)° towards the plane of the azoxy group; the torsion angles along the Ar—N bond in the β isomer are 24.3 (3) and 23.5 (3)°. Quantum-mechanical calculations indicate that planar conformations are energetically favourable for both isomers. The N—H
O hydrogen bonds observed in both networks may be responsible for the deformation of these flexible molecules.
Supporting information
CCDC references: 195616; 195617
trans-4-(N-Acetylamino)-azobenzene was oxidized with hydrogen
peroxide in a mixture of acetic acid and acetic anhydride, as described by
Domański et al. (2001). The crude product was hydrolysed and
chromatographed. The homogenous fractions were evaporated to dryness and the
residues were crystallized from methanol, providing crystals of (I) and (II)
suitable for X-ray diffraction studies. The orthorhombic polymorphs of the
trans-4-aminoazoxybenzenes were obtained by the above crystallization
from methanol. When non-polar solvents were used, the monoclinic forms were
obtained. The polymorphs of the isomers were examined by differential scanning
calorimetry (DSC). The orthorhombic crystals contain no solvent molecules,
although interactions with the solvent must have played an important role in
growing the crystals. Their melting points, expressed as minima on the DSC
curves, are higher (α 416.2–417.7 K and β 418.5 K) than those of the
monoclinic polymorphs (α 408.9 K and β 407 K). Phase transitions of one
polymorph into another were not observed.
Quantum-mechanical calculations were carried out using GAUSSIAN98 (Frisch
et al., 1998). Geometry optimization was performed with the Becke 3LYP
density functional theory (DFT) hybrid method (Lee et al., 1988; Becke,
1993) in combination with the 6–31G** basis set. The fully relaxed (Φ-Ψ)
conformational energy map in vacuo (30° spacing) of (II) was obtained
by the HF method with the 3–21 G basis set. H-atom coordinates were refined,
giving C—H distances in the range 0.89 (3)–1.05 (1) Å and N—H distances
in the range 0.89 (3)–0.95 (2) Å.
For both compounds, data collection: KM-4 CCD Software (Kuma Diffraction, 1999); cell refinement: KM-4 CCD Software; data reduction: KM-4 CCD Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1990); software used to prepare material for publication: SHELXL97.
(I) 1-(4-aminophenyl)-2-phenyldiazene 2-oxide
top
Crystal data top
C12H11N3O | F(000) = 896 |
Mr = 213.24 | Dx = 1.365 Mg m−3 |
Orthorhombic, Pbca | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ac 2ab | Cell parameters from 3160 reflections |
a = 12.058 (2) Å | θ = 3.5–26.0° |
b = 7.054 (1) Å | µ = 0.09 mm−1 |
c = 24.398 (5) Å | T = 90 K |
V = 2075.2 (6) Å3 | Prism, orange |
Z = 8 | 0.40 × 0.25 × 0.13 mm |
Data collection top
Kuma KM-4 with two-dimensional CCD area-detector diffractometer | 1617 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.034 |
Graphite monochromator | θmax = 26.0°, θmin = 3.5° |
Detector resolution: 1024x1024 with blocks 2x2 pixels mm-1 | h = −14→14 |
ω scans | k = −8→6 |
12684 measured reflections | l = −30→28 |
2030 independent reflections | |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.042 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.112 | All H-atom parameters refined |
S = 1.11 | w = 1/[σ2(Fo2) + (0.0671P)2 + 0.1381P] where P = (Fo2 + 2Fc2)/3 |
2030 reflections | (Δ/σ)max = 0.001 |
191 parameters | Δρmax = 0.31 e Å−3 |
0 restraints | Δρmin = −0.18 e Å−3 |
Crystal data top
C12H11N3O | V = 2075.2 (6) Å3 |
Mr = 213.24 | Z = 8 |
Orthorhombic, Pbca | Mo Kα radiation |
a = 12.058 (2) Å | µ = 0.09 mm−1 |
b = 7.054 (1) Å | T = 90 K |
c = 24.398 (5) Å | 0.40 × 0.25 × 0.13 mm |
Data collection top
Kuma KM-4 with two-dimensional CCD area-detector diffractometer | 1617 reflections with I > 2σ(I) |
12684 measured reflections | Rint = 0.034 |
2030 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.042 | 0 restraints |
wR(F2) = 0.112 | All H-atom parameters refined |
S = 1.11 | Δρmax = 0.31 e Å−3 |
2030 reflections | Δρmin = −0.18 e Å−3 |
191 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 | x | y | z | Uiso*/Ueq | |
N1 | 1.03622 (10) | 0.22089 (19) | 0.58438 (6) | 0.0256 (4) | |
N2 | 0.93829 (11) | 0.20682 (19) | 0.60288 (6) | 0.0262 (3) | |
O1 | 1.12684 (9) | 0.21446 (17) | 0.61182 (5) | 0.0303 (3) | |
C1 | 0.92224 (13) | 0.1715 (2) | 0.65905 (6) | 0.0234 (4) | |
C2 | 0.99093 (14) | 0.0673 (2) | 0.69493 (6) | 0.0240 (4) | |
C3 | 0.95795 (13) | 0.0352 (2) | 0.74829 (7) | 0.0231 (4) | |
C4 | 0.85716 (13) | 0.1060 (2) | 0.76819 (6) | 0.0223 (4) | |
C5 | 0.78915 (13) | 0.2084 (2) | 0.73222 (7) | 0.0245 (4) | |
C6 | 0.82079 (13) | 0.2373 (2) | 0.67901 (7) | 0.0245 (4) | |
N3 | 0.82633 (13) | 0.0769 (2) | 0.82143 (6) | 0.0307 (4) | |
C1' | 1.04477 (13) | 0.2524 (2) | 0.52500 (7) | 0.0243 (4) | |
C2' | 1.14561 (15) | 0.3095 (3) | 0.50438 (7) | 0.0357 (5) | |
C3' | 1.15634 (15) | 0.3386 (3) | 0.44821 (7) | 0.0388 (5) | |
C4' | 1.06694 (14) | 0.3096 (2) | 0.41366 (7) | 0.0297 (4) | |
C5' | 0.96671 (15) | 0.2527 (3) | 0.43516 (8) | 0.0335 (4) | |
C6' | 0.95509 (15) | 0.2239 (3) | 0.49113 (8) | 0.0323 (4) | |
H2 | 1.0605 (14) | 0.016 (2) | 0.6830 (6) | 0.026 (4)* | |
H3 | 1.0023 (14) | −0.035 (3) | 0.7718 (7) | 0.024 (4)* | |
H5 | 0.7162 (15) | 0.255 (3) | 0.7450 (7) | 0.030 (5)* | |
H6 | 0.7736 (14) | 0.311 (3) | 0.6540 (7) | 0.030 (4)* | |
H31 | 0.8538 (16) | −0.024 (3) | 0.8408 (9) | 0.048 (6)* | |
H32 | 0.7525 (18) | 0.107 (3) | 0.8322 (8) | 0.056 (6)* | |
H2' | 1.2060 (17) | 0.326 (3) | 0.5304 (8) | 0.044 (6)* | |
H3' | 1.2311 (18) | 0.380 (3) | 0.4342 (8) | 0.054 (6)* | |
H4' | 1.0720 (10) | 0.3304 (19) | 0.3713 (6) | 0.003 (3)* | |
H5' | 0.9041 (16) | 0.236 (3) | 0.4108 (8) | 0.044 (6)* | |
H6' | 0.8879 (18) | 0.187 (3) | 0.5065 (8) | 0.048 (6)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
N1 | 0.0211 (7) | 0.0266 (7) | 0.0289 (8) | 0.0023 (6) | −0.0026 (5) | −0.0027 (6) |
N2 | 0.0244 (7) | 0.0260 (7) | 0.0279 (8) | 0.0017 (6) | −0.0008 (6) | 0.0004 (6) |
O1 | 0.0188 (6) | 0.0454 (7) | 0.0265 (6) | −0.0024 (5) | −0.0061 (5) | 0.0034 (5) |
C1 | 0.0288 (9) | 0.0210 (8) | 0.0199 (8) | −0.0033 (7) | −0.0025 (6) | −0.0013 (6) |
C2 | 0.0226 (9) | 0.0230 (8) | 0.0264 (9) | 0.0021 (7) | 0.0015 (6) | −0.0017 (7) |
C3 | 0.0237 (8) | 0.0209 (8) | 0.0243 (8) | 0.0014 (7) | −0.0040 (6) | 0.0017 (7) |
C4 | 0.0246 (8) | 0.0202 (8) | 0.0220 (8) | −0.0034 (7) | −0.0003 (6) | −0.0034 (6) |
C5 | 0.0208 (8) | 0.0207 (8) | 0.0316 (9) | 0.0013 (7) | −0.0019 (6) | −0.0040 (7) |
C6 | 0.0248 (9) | 0.0208 (8) | 0.0276 (9) | 0.0007 (7) | −0.0061 (7) | −0.0011 (7) |
N3 | 0.0312 (9) | 0.0360 (9) | 0.0247 (8) | 0.0040 (7) | 0.0033 (6) | 0.0000 (7) |
C1' | 0.0290 (9) | 0.0226 (8) | 0.0210 (8) | 0.0057 (7) | 0.0008 (6) | 0.0004 (6) |
C2' | 0.0260 (9) | 0.0566 (12) | 0.0243 (9) | 0.0018 (8) | −0.0010 (7) | −0.0027 (8) |
C3' | 0.0295 (10) | 0.0593 (13) | 0.0273 (10) | −0.0007 (9) | 0.0058 (7) | 0.0004 (9) |
C4' | 0.0357 (10) | 0.0313 (9) | 0.0221 (9) | 0.0080 (7) | 0.0002 (7) | −0.0011 (7) |
C5' | 0.0320 (10) | 0.0375 (10) | 0.0306 (10) | 0.0028 (8) | −0.0068 (8) | 0.0007 (8) |
C6' | 0.0267 (10) | 0.0391 (11) | 0.0306 (10) | −0.0014 (8) | 0.0009 (7) | 0.0052 (8) |
Geometric parameters (Å, º) top
N1—N2 | 1.268 (2) | C6—H6 | 0.98 (2) |
N1—O1 | 1.282 (2) | N3—H31 | 0.92 (2) |
N1—C1' | 1.469 (2) | N3—H32 | 0.95 (2) |
N2—C1 | 1.406 (2) | C1'—C6' | 1.376 (2) |
C1—C6 | 1.396 (2) | C1'—C2' | 1.376 (2) |
C1—C2 | 1.412 (2) | C2'—C3' | 1.392 (2) |
C2—C3 | 1.380 (2) | C2'—H2' | 0.97 (2) |
C2—H2 | 0.96 (2) | C3'—C4' | 1.384 (2) |
C3—C4 | 1.401 (2) | C3'—H3' | 1.01 (2) |
C3—H3 | 0.93 (2) | C4'—C5' | 1.377 (3) |
C4—N3 | 1.367 (2) | C4'—H4' | 1.05 (1) |
C4—C5 | 1.402 (2) | C5'—C6' | 1.388 (3) |
C5—C6 | 1.368 (2) | C5'—H5' | 0.97 (2) |
C5—H5 | 0.99 (2) | C6'—H6' | 0.93 (2) |
| | | |
N2—N1—O1 | 127.2 (1) | C4—N3—H31 | 120 (1) |
N2—N1—C1' | 115.4 (1) | C4—N3—H32 | 119 (1) |
O1—N1—C1' | 117.4 (1) | H31—N3—H32 | 112 (2) |
N1—N2—C1 | 119.3 (1) | C6'—C1'—C2' | 121.2 (2) |
C6—C1—N2 | 113.7 (1) | C6'—C1'—N1 | 121.0 (2) |
C6—C1—C2 | 118.1 (1) | C2'—C1'—N1 | 117.8 (1) |
N2—C1—C2 | 128.0 (1) | C1'—C2'—C3' | 119.0 (2) |
C3—C2—C1 | 120.1 (2) | C1'—C2'—H2' | 117 (1) |
C3—C2—H2 | 118 (1) | C3'—C2'—H2' | 124 (1) |
C1—C2—H2 | 122 (1) | C4'—C3'—C2' | 120.4 (2) |
C2—C3—C4 | 121.2 (2) | C4'—C3'—H3' | 122 (1) |
C2—C3—H3 | 120 (1) | C2'—C3'—H3' | 117 (1) |
C4—C3—H3 | 119 (1) | C5'—C4'—C3' | 119.7 (2) |
N3—C4—C3 | 120.8 (2) | C5'—C4'—H4' | 118 (1) |
N3—C4—C5 | 120.9 (2) | C3'—C4'—H4' | 122 (1) |
C3—C4—C5 | 118.3 (1) | C4'—C5'—C6' | 120.4 (2) |
C6—C5—C4 | 120.5 (2) | C4'—C5'—H5' | 119 (1) |
C6—C5—H5 | 120 (1) | C6'—C5'—H5' | 121 (1) |
C4—C5—H5 | 120 (1) | C1'—C6'—C5' | 119.4 (2) |
C5—C6—C1 | 121.7 (2) | C1'—C6'—H6' | 119 (1) |
C5—C6—H6 | 120 (1) | C5'—C6'—H6' | 122 (1) |
C1—C6—H6 | 118 (1) | | |
| | | |
O1—N1—N2—C1 | −3.2 (2) | C2—C1—C6—C5 | 2.2 (2) |
C1'—N1—N2—C1 | 178.3 (1) | N2—N1—C1'—C6' | −14.4 (2) |
N1—N2—C1—C6 | 154.0 (1) | O1—N1—C1'—C6' | 166.9 (2) |
N1—N2—C1—C2 | −31.5 (2) | N2—N1—C1'—C2' | 166.1 (2) |
C6—C1—C2—C3 | −0.9 (2) | O1—N1—C1'—C2' | −12.5 (2) |
N2—C1—C2—C3 | −175.2 (2) | C6'—C1'—C2'—C3' | 0.0 (3) |
C1—C2—C3—C4 | −0.7 (2) | N1—C1'—C2'—C3' | 179.4 (2) |
C2—C3—C4—N3 | −178.6 (2) | C1'—C2'—C3'—C4' | −0.3 (3) |
C2—C3—C4—C5 | 1.0 (2) | C2'—C3'—C4'—C5' | 0.4 (3) |
N3—C4—C5—C6 | 179.8 (2) | C3'—C4'—C5'—C6' | −0.2 (3) |
C3—C4—C5—C6 | 0.2 (2) | C2'—C1'—C6'—C5' | 0.2 (3) |
C4—C5—C6—C1 | −1.9 (2) | N1—C1'—C6'—C5' | −179.2 (2) |
N2—C1—C6—C5 | 177.3 (1) | C4'—C5'—C6'—C1' | −0.1 (3) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H31···O1i | 0.92 (2) | 2.19 (2) | 3.083 (2) | 165 (2) |
N3—H32···O1ii | 0.95 (2) | 2.18 (2) | 3.063 (2) | 154 (2) |
Symmetry codes: (i) −x+2, y−1/2, −z+3/2; (ii) x−1/2, y, −z+3/2. |
(II) 2-(4-aminophenyl)-1-phenyldiazene 2-oxide
top
Crystal data top
C12H11N3O | F(000) = 448 |
Mr = 213.24 | Dx = 1.351 Mg m−3 |
Orthorhombic, Pca21 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2c -2ac | Cell parameters from 1630 reflections |
a = 17.779 (4) Å | θ = 3.7–25.5° |
b = 5.535 (1) Å | µ = 0.09 mm−1 |
c = 10.652 (2) Å | T = 90 K |
V = 1048.2 (4) Å3 | Prism, yellow |
Z = 4 | 0.25 × 0.14 × 0.12 mm |
Data collection top
Kuma KM-4 with two-dimensional CCD area-detector diffractometer | 971 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.047 |
Graphite monochromator | θmax = 25.5°, θmin = 3.7° |
Detector resolution: 1024x1024 with blocks 2x2 pixels mm-1 | h = −21→21 |
ω scans | k = −4→6 |
6087 measured reflections | l = −12→12 |
1033 independent reflections | |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.031 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.067 | All H-atom parameters refined |
S = 1.06 | w = 1/[σ2(Fo2) + (0.0422P)2] where P = (Fo2 + 2Fc2)/3 |
1033 reflections | (Δ/σ)max < 0.001 |
189 parameters | Δρmax = 0.14 e Å−3 |
1 restraint | Δρmin = −0.16 e Å−3 |
Crystal data top
C12H11N3O | V = 1048.2 (4) Å3 |
Mr = 213.24 | Z = 4 |
Orthorhombic, Pca21 | Mo Kα radiation |
a = 17.779 (4) Å | µ = 0.09 mm−1 |
b = 5.535 (1) Å | T = 90 K |
c = 10.652 (2) Å | 0.25 × 0.14 × 0.12 mm |
Data collection top
Kuma KM-4 with two-dimensional CCD area-detector diffractometer | 971 reflections with I > 2σ(I) |
6087 measured reflections | Rint = 0.047 |
1033 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.031 | 1 restraint |
wR(F2) = 0.067 | All H-atom parameters refined |
S = 1.06 | Δρmax = 0.14 e Å−3 |
1033 reflections | Δρmin = −0.16 e Å−3 |
189 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 | x | y | z | Uiso*/Ueq | |
N1 | 0.33494 (10) | 0.3120 (3) | 0.08364 (17) | 0.0184 (4) | |
N2 | 0.30226 (11) | 0.1672 (3) | 0.00566 (18) | 0.0189 (4) | |
N3 | 0.56451 (12) | 0.9054 (4) | −0.1173 (2) | 0.0245 (5) | |
O1 | 0.32237 (9) | 0.3354 (3) | 0.20214 (15) | 0.0257 (4) | |
C1 | 0.39418 (12) | 0.4655 (4) | 0.0301 (2) | 0.0187 (5) | |
C2 | 0.41356 (12) | 0.6791 (4) | 0.0928 (2) | 0.0188 (5) | |
C3 | 0.47079 (13) | 0.8243 (4) | 0.0451 (2) | 0.0195 (5) | |
C4 | 0.50954 (12) | 0.7595 (4) | −0.0660 (2) | 0.0192 (5) | |
C5 | 0.48904 (13) | 0.5406 (4) | −0.1269 (2) | 0.0197 (5) | |
C6 | 0.43173 (13) | 0.3961 (4) | −0.0805 (2) | 0.0199 (5) | |
C1' | 0.24549 (13) | 0.0068 (3) | 0.0506 (2) | 0.0192 (5) | |
C2' | 0.19978 (13) | 0.0337 (4) | 0.1586 (2) | 0.0206 (5) | |
C3' | 0.14420 (13) | −0.1402 (4) | 0.1831 (2) | 0.0210 (5) | |
C4' | 0.13417 (13) | −0.3398 (4) | 0.1029 (2) | 0.0223 (5) | |
C5' | 0.17917 (13) | −0.3650 (4) | −0.0042 (2) | 0.0214 (5) | |
C6' | 0.23349 (14) | −0.1914 (4) | −0.0317 (2) | 0.0192 (5) | |
H2 | 0.3872 (13) | 0.720 (4) | 0.168 (2) | 0.021 (6)* | |
H3 | 0.4859 (14) | 0.983 (5) | 0.087 (3) | 0.026 (6)* | |
H31 | 0.5825 (16) | 1.027 (5) | −0.069 (3) | 0.041 (9)* | |
H32 | 0.5947 (16) | 0.844 (5) | −0.176 (3) | 0.039 (9)* | |
H5 | 0.5148 (14) | 0.493 (4) | −0.202 (2) | 0.027 (7)* | |
H6 | 0.4181 (15) | 0.244 (5) | −0.123 (3) | 0.033 (7)* | |
H2' | 0.2066 (14) | 0.173 (4) | 0.218 (3) | 0.031 (7)* | |
H4' | 0.0965 (15) | −0.466 (4) | 0.120 (3) | 0.032 (7)* | |
H3' | 0.1096 (14) | −0.126 (4) | 0.259 (3) | 0.031 (7)* | |
H5' | 0.1735 (13) | −0.502 (4) | −0.060 (3) | 0.022 (6)* | |
H6' | 0.2639 (16) | −0.203 (4) | −0.109 (3) | 0.024 (7)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
N1 | 0.0180 (9) | 0.0197 (9) | 0.0174 (11) | 0.0002 (8) | −0.0012 (9) | 0.0005 (9) |
N2 | 0.0175 (10) | 0.0183 (9) | 0.0209 (10) | −0.0002 (8) | −0.0010 (8) | −0.0001 (8) |
N3 | 0.0223 (11) | 0.0242 (11) | 0.0269 (12) | −0.0042 (9) | 0.0014 (10) | −0.0004 (9) |
O1 | 0.0266 (9) | 0.0351 (9) | 0.0155 (9) | −0.0049 (8) | 0.0013 (7) | −0.0026 (8) |
C1 | 0.0133 (11) | 0.0205 (11) | 0.0223 (13) | −0.0002 (9) | −0.0028 (9) | 0.0038 (10) |
C2 | 0.0175 (11) | 0.0207 (11) | 0.0182 (11) | 0.0033 (10) | −0.0032 (10) | −0.0004 (10) |
C3 | 0.0174 (11) | 0.0182 (11) | 0.0228 (12) | 0.0016 (9) | −0.0043 (10) | −0.0013 (10) |
C4 | 0.0148 (10) | 0.0210 (11) | 0.0219 (12) | 0.0008 (10) | −0.0047 (10) | 0.0044 (9) |
C5 | 0.0207 (11) | 0.0227 (11) | 0.0157 (12) | 0.0052 (9) | 0.0003 (10) | −0.0005 (10) |
C6 | 0.0197 (11) | 0.0199 (11) | 0.0200 (12) | 0.0027 (9) | −0.0032 (10) | 0.0004 (10) |
C1' | 0.0184 (11) | 0.0189 (10) | 0.0203 (12) | 0.0011 (10) | −0.0034 (9) | 0.0046 (10) |
C2' | 0.0207 (11) | 0.0203 (11) | 0.0208 (12) | 0.0030 (9) | −0.0006 (10) | −0.0008 (11) |
C3' | 0.0194 (12) | 0.0244 (12) | 0.0191 (13) | −0.0014 (10) | 0.0019 (10) | 0.0001 (10) |
C4' | 0.0191 (12) | 0.0225 (12) | 0.0253 (13) | −0.0011 (11) | −0.0009 (10) | 0.0023 (10) |
C5' | 0.0214 (13) | 0.0183 (11) | 0.0246 (13) | 0.0005 (9) | −0.0032 (10) | −0.0017 (11) |
C6' | 0.0169 (12) | 0.0211 (11) | 0.0197 (12) | 0.0047 (9) | −0.0026 (9) | −0.0008 (10) |
Geometric parameters (Å, º) top
N1—O1 | 1.288 (2) | C5—C6 | 1.387 (3) |
N1—N2 | 1.292 (2) | C5—H5 | 0.96 (3) |
N1—C1 | 1.469 (3) | C6—H6 | 0.98 (3) |
N2—C1' | 1.427 (3) | C1'—C2' | 1.416 (3) |
N3—C4 | 1.381 (3) | C1'—C6' | 1.421 (3) |
N3—H31 | 0.91 (3) | C2'—C3' | 1.404 (3) |
N3—H32 | 0.89 (3) | C2'—H2' | 1.00 (3) |
C1—C2 | 1.401 (3) | C3'—C4' | 1.408 (3) |
C1—C6 | 1.408 (3) | C3'—H3' | 1.02 (3) |
C2—C3 | 1.393 (3) | C4'—C5' | 1.400 (4) |
C2—H2 | 0.96 (3) | C4'—H4' | 0.98 (3) |
C3—C4 | 1.416 (3) | C5'—C6' | 1.393 (3) |
C3—H3 | 1.02 (3) | C5'—H5' | 0.97 (2) |
C4—C5 | 1.422 (3) | C6'—H6' | 0.99 (3) |
| | | |
O1—N1—N2 | 127.9 (2) | C5—C6—C1 | 119.3 (2) |
O1—N1—C1 | 116.5 (2) | C5—C6—H6 | 120.8 (16) |
N2—N1—C1 | 115.6 (2) | C1—C6—H6 | 119.9 (16) |
N1—N2—C1' | 119.2 (2) | C2'—C1'—C6' | 119.8 (2) |
C4—N3—H31 | 117.1 (19) | C2'—C1'—N2 | 127.8 (2) |
C4—N3—H32 | 118.6 (18) | C6'—C1'—N2 | 112.3 (2) |
H31—N3—H32 | 118 (3) | C3'—C2'—C1' | 118.9 (2) |
C2—C1—C6 | 120.9 (2) | C3'—C2'—H2' | 119.7 (15) |
C2—C1—N1 | 118.6 (2) | C1'—C2'—H2' | 121.5 (15) |
C6—C1—N1 | 120.5 (2) | C2'—C3'—C4' | 120.9 (2) |
C3—C2—C1 | 119.5 (2) | C2'—C3'—H3' | 121.4 (15) |
C3—C2—H2 | 121.9 (15) | C4'—C3'—H3' | 117.6 (15) |
C1—C2—H2 | 118.6 (15) | C5'—C4'—C3' | 120.0 (2) |
C2—C3—C4 | 121.0 (2) | C5'—C4'—H4' | 117.8 (15) |
C2—C3—H3 | 121.9 (15) | C3'—C4'—H4' | 122.2 (15) |
C4—C3—H3 | 117.2 (16) | C6'—C5'—C4' | 119.9 (2) |
N3—C4—C3 | 121.8 (2) | C6'—C5'—H5' | 119.1 (14) |
N3—C4—C5 | 119.9 (2) | C4'—C5'—H5' | 121.0 (14) |
C3—C4—C5 | 118.2 (2) | C5'—C6'—C1' | 120.4 (2) |
C6—C5—C4 | 121.2 (2) | C5'—C6'—H6' | 120.5 (14) |
C6—C5—H5 | 119.4 (15) | C1'—C6'—H6' | 119.1 (14) |
C4—C5—H5 | 119.5 (15) | | |
| | | |
O1—N1—N2—C1' | −0.9 (3) | C4—C5—C6—C1 | −1.1 (3) |
C1—N1—N2—C1' | 178.23 (18) | C2—C1—C6—C5 | 0.6 (3) |
O1—N1—C1—C2 | −22.8 (3) | N1—C1—C6—C5 | −178.00 (19) |
N2—N1—C1—C2 | 157.9 (2) | N1—N2—C1'—C2' | 24.3 (3) |
O1—N1—C1—C6 | 155.77 (19) | N1—N2—C1'—C6' | −159.9 (2) |
N2—N1—C1—C6 | −23.5 (3) | C6'—C1'—C2'—C3' | 1.3 (3) |
C6—C1—C2—C3 | −0.1 (3) | N2—C1'—C2'—C3' | 176.8 (2) |
N1—C1—C2—C3 | 178.52 (19) | C1'—C2'—C3'—C4' | 0.6 (3) |
C1—C2—C3—C4 | 0.2 (3) | C2'—C3'—C4'—C5' | −1.0 (3) |
C2—C3—C4—N3 | 177.6 (2) | C3'—C4'—C5'—C6' | −0.4 (3) |
C2—C3—C4—C5 | −0.7 (3) | C4'—C5'—C6'—C1' | 2.3 (3) |
N3—C4—C5—C6 | −177.1 (2) | C2'—C1'—C6'—C5' | −2.7 (3) |
C3—C4—C5—C6 | 1.2 (3) | N2—C1'—C6'—C5' | −178.9 (2) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H32···O1i | 0.89 (3) | 2.20 (3) | 3.085 (3) | 172 (3) |
N3—H31···Cg2ii | 0.91 (3) | 2.56 (3) | 3.357 (3) | 146 (3) |
Symmetry codes: (i) −x+1, −y+1, z−1/2; (ii) −x+1/2, y+1, z+1/2. |
Experimental details
| (I) | (II) |
Crystal data |
Chemical formula | C12H11N3O | C12H11N3O |
Mr | 213.24 | 213.24 |
Crystal system, space group | Orthorhombic, Pbca | Orthorhombic, Pca21 |
Temperature (K) | 90 | 90 |
a, b, c (Å) | 12.058 (2), 7.054 (1), 24.398 (5) | 17.779 (4), 5.535 (1), 10.652 (2) |
V (Å3) | 2075.2 (6) | 1048.2 (4) |
Z | 8 | 4 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 0.09 | 0.09 |
Crystal size (mm) | 0.40 × 0.25 × 0.13 | 0.25 × 0.14 × 0.12 |
|
Data collection |
Diffractometer | Kuma KM-4 with two-dimensional CCD area-detector diffractometer | Kuma KM-4 with two-dimensional CCD area-detector diffractometer |
Absorption correction | – | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 12684, 2030, 1617 | 6087, 1033, 971 |
Rint | 0.034 | 0.047 |
(sin θ/λ)max (Å−1) | 0.617 | 0.606 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.042, 0.112, 1.11 | 0.031, 0.067, 1.06 |
No. of reflections | 2030 | 1033 |
No. of parameters | 191 | 189 |
No. of restraints | 0 | 1 |
H-atom treatment | All H-atom parameters refined | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 0.31, −0.18 | 0.14, −0.16 |
Selected geometric parameters (Å, º) for (I) topN1—N2 | 1.268 (2) | N2—C1 | 1.406 (2) |
N1—O1 | 1.282 (2) | C4—N3 | 1.367 (2) |
N1—C1' | 1.469 (2) | | |
| | | |
N2—N1—O1 | 127.2 (1) | C6—C1—N2 | 113.7 (1) |
N2—N1—C1' | 115.4 (1) | N2—C1—C2 | 128.0 (1) |
O1—N1—C1' | 117.4 (1) | C6'—C1'—N1 | 121.0 (2) |
N1—N2—C1 | 119.3 (1) | C2'—C1'—N1 | 117.8 (1) |
| | | |
N1—N2—C1—C6 | 154.0 (1) | N2—N1—C1'—C6' | −14.4 (2) |
N1—N2—C1—C2 | −31.5 (2) | N2—N1—C1'—C2' | 166.1 (2) |
Hydrogen-bond geometry (Å, º) for (I) top
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H31···O1i | 0.92 (2) | 2.19 (2) | 3.083 (2) | 165 (2) |
N3—H32···O1ii | 0.95 (2) | 2.18 (2) | 3.063 (2) | 154 (2) |
Symmetry codes: (i) −x+2, y−1/2, −z+3/2; (ii) x−1/2, y, −z+3/2. |
Selected geometric parameters (Å, º) for (II) topN1—O1 | 1.288 (2) | N2—C1' | 1.427 (3) |
N1—N2 | 1.292 (2) | N3—C4 | 1.381 (3) |
N1—C1 | 1.469 (3) | | |
| | | |
O1—N1—N2 | 127.9 (2) | C2—C1—N1 | 118.6 (2) |
O1—N1—C1 | 116.5 (2) | C6—C1—N1 | 120.5 (2) |
N2—N1—C1 | 115.6 (2) | C2'—C1'—N2 | 127.8 (2) |
N1—N2—C1' | 119.2 (2) | C6'—C1'—N2 | 112.3 (2) |
| | | |
N2—N1—C1—C2 | 157.9 (2) | N1—N2—C1'—C2' | 24.3 (3) |
N2—N1—C1—C6 | −23.5 (3) | N1—N2—C1'—C6' | −159.9 (2) |
Hydrogen-bond geometry (Å, º) for (II) top
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H32···O1i | 0.89 (3) | 2.20 (3) | 3.085 (3) | 172 (3) |
N3—H31···Cg2ii | 0.91 (3) | 2.56 (3) | 3.357 (3) | 146 (3) |
Symmetry codes: (i) −x+1, −y+1, z−1/2; (ii) −x+1/2, y+1, z+1/2. |
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The most effective method of preparation of azoxybenzene and its derivatives involves oxidation of the corresponding azobenzenes. The reaction is not regioselective, and consequently an unsymmetrical substrate gives a mixture of the two isomers. The separation and identification of these isomers is difficult in most cases (Domański & Kyzioł, 2001); X-ray diffraction is the only reliable method of assigning the structure of a particular isomer. We have established the molecular and crystal structures of the monoclinic forms of NNO and ONN trans-4-aminoazoxybenzenes (Domański et al., 2001) but, in further experiments, the same compounds were obtained in different forms displaying higher melting points. Structural investigations revealed that the orthorhombic polymorphs of the isomers arise from crystallization using polar solvents, whereas the monoclinic polymorphs have been obtained by crystallization from non-polar solvents. We present here the molecular and crystal structures of the orthorhombic polymorphs, 4-amino-ONN-azoxybenzene (α isomer), (I), and 4-amino-NNO-azoxybenzene (β isomer), (II). \sch
The molecular structures of the title compounds are shown in Figs. 1a [α isomer, compound (I] and 1 b [β isomer, compound (II)]. The geometry of the bridge is nearly the same in both forms and both isomers. However, the N1—O1 bond is significantly longer (0.03 Å) in the orthorhombic form of the β isomer in comparison with the monoclinic form. Analogous differences are observed in the N1—N2 bond; these are limited to the β (NNO) isomer. The bonds between the bridge and the aromatic rings are of the same length in both isomers and both polymorphs. In all cases, the bond on the oxidized side of the bridge is ca 0.04 Å longer than another one.
The valence angles are typical for the trigonal hybridization of the C and N atoms of the bridge. Some deviations (e.g. 128.2 versus 113.7°) are observed within the C—C—N angles on the unoxidized side of the azoxy group. Such a deformation results from steric interaction between O1 and the H atom in the ortho position.
There are typical features observed in the molecular structures of trans-azoxybenzenes (Domański et al., 2001; Hoesch & Weber, 1977; Krigbaum & Barber, 1971, 1974). There seems to be little evidence for the existence of C—H···O hydrogen bonds, when the shortest O···H distances are 2.37 (2) and 2.34 (2) Å in (I), and 2.45 (2) and 2.25 (2) Å in (II). These distances are shorter than the sum of the van der Waals radii (2.6 Å) given by Pauling (1967).
The sum of the valence angles around the amino N atom [ca 351° in (I) and 354° in (II)], and the distance of atom N3 from the C4/H31/H32 plane [0.18 (1) and 0.15 (1) Å for (I) and (II), respectively], indicate a lack of mesomeric interaction between the amino group and the aromatic ring. The planarity of the amino group has been analysed by two functions of the torsion angles, τ and χN (Ferretti et al., 1993), defined as τ = (ω1 + ω2)/2, characterizing the rotation around the C—N bond, and χN = ω2 - ω3 + π(mode 2π), being a measure of the degree of pyramidalization of the N atom (where ω1 = C5—C4—N3—H32, ω2 = C3—C4—N3—H31 and ω3 = C3—C4—N3—H32). These values are τ = 7° and χN = 35° in (I), and 1.5 and 29°, respectively, in (II). In both isomers, the χN values are intermediate between the extreme value for a regular tetrahedral sp3 configuration (60°) and 0, corresponding to a planar sp2 hybridization. In the monoclinic forms, the χN factor was bigger in the β isomer (46°) than in the α isomer (26°). It was inferred that the amino group situated on the unoxidized side of the azoxy bridge was more planar (Domański et al., 2001). The dihedral angles between the amino group and the benzene ring are 28 (2)° in (I) and 23 (3)° in (II).
Three planar fragments in the molecular structure of these compounds may be distinguished, namely the benzene ring connected to atom N1 (A), the azoxy group (B) and the other benzene ring (C). In the α isomer, the dihedral angles between the various groups are A/B 13.6 (1), B/C 30.6 (1) and A/C 43.7 (1)°; the analogous values for the β isomer are 23.3 (2), 21.7 (2) and 1.8 (1)°, respectively. Additionally, the twists along the Caryl—N bonds are observed by the values of the torsion angles of -31.5 (2) and -14.4 (2) for the α isomer, and 24.3 (3) and -23.5 (3)° for the β isomer. These torsion angles are the most significant differences in the conformations of the molecules in the orthorhombic and monoclinic forms. Such conformations exclude effective conjugation between the amino and azoxy groups across the ring, which was suggested in our previous paper (Domański et al., 2001). Steric hindrance around the azoxy group influences the conformations of the molecules, but intermolecular interactions within the crystal network seem to be important as well.
Azoxyarene molecules used to be considered as planar, and hence relatively large torsion angles along the Ar—N bonds were surprising. The results of quantum-mechanical calculations by the B3LYP/6–31G** method (Frisch et al., 1998) are in agreement with this intuitive picture: planar conformations are the most stable for both isomers. The conformational energy contour map (Fig. 2) demonstrates that the conformation with both rings perpendicular to the azoxy bridge is the most unfavourable (20 kcal mol-1; 1 kcal = 4.184 kJ). However, deviations from planarity observed in the crystal network cause a total energy increase of 1.08 kcal mol-1 in (II) and 1.51 kcal mol-1 in (I). Please check rephrasing. Consequently, the conformations of (I) and (II) in the orthorhombic and monoclinic networks may result from intermolecular interactions.
N—H···O hydrogen bonds are observed in both pairs of isomers. The molecular packing of the α and β isomers, with hydrogen bonds shown by dashed lines, is shown in Fig. 3. The IR spectra of the isomers are very similar in the high-wavenumber region, but the spectra of pairs of polymorphs are indistinguishable, e.g. 3447 and 3351 versus 3447 and 3350 cm-1 in the case of the α isomer. The geometric parameters of the hydrogen bonds confirm the spectroscopic data. In both pairs, the interactions are weak and electrostatic in nature (Desiraju & Steiner, 1999). In spite of this, a closer approach of one molecule to another may cause deformation from the planar conformation in some cases.
In Table 4, Cg2 is the centroid of the unsubstituted ring C1'-C6'.