organic compounds
2,2′-({4-[(4-Nitrophenyl)diazenyl]phenyl}imino)diethanol
aDepartment of Chemistry, Faculty of Science, Kasetsart University, Bangkok 10903, Thailand, and bDepartment of Textile Science, Faculty of Agro-Industry, Kasetsart University, Bangkok 10900, Thailand
*Correspondence e-mail: fsciska@ku.ac.th
In the title compound, C16H18N4O4, the molecule assumes an E conformation with respect to the N=N double bond. The aromatic rings are not coplanar, with a dihedral angle of 7.51 (8)°. The nitro group is tilted by 4.71 (11)° relative to the attached benzene ring. In the crystal, molecules are connected through O—H⋯O hydrogen bonds forming a double-stranded chain parallel to the b axis.
Related literature
For the properties of azo disperse dyes, see: Suesat et al. (2011). For the structure of related compounds, see: Zhang et al. (1998); Adams et al. (2004).
Experimental
Crystal data
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Data collection
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Refinement
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Data collection: APEX2 (Bruker, 2011); cell SAINT (Bruker, 2011); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.
Supporting information
https://doi.org/10.1107/S1600536812049239/rz5028sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536812049239/rz5028Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S1600536812049239/rz5028Isup3.cml
The azo disperse dye was prepared by dissolving 4-nitroaniline (0.01 mol) in 50 ml of an acetic acid/propionic acid (43:7 v/v) mixture. The solution was stirred and the temperature was kept in the range of 0–5°C. Diazotization took place when nitrosyl sulfuric acid (HNO5S) was added to the solution and stirred at 0–5°C for 30–60 minutes. The coupling component N-bis-β-hydroxyethyl aniline (0.01 mol) was then dissolved in 40 ml acetone, distilled water was added to make the total volume of 200 ml and sulfamic acid (0.5 g) was added. The coupling reaction was performed by slow addition of the diazonium salt solution to the coupling solution at 0–5°C. The reaction continued for 2 h with stirring and was monitored using TLC. On completion of the coupling reaction, the dye precipitate was collected by filtration and dried at room temperature. The dye was purified by recrystallization in n-propanol. Single crystals suitable for X-ray analysis were obtained by slow evaporation of a purified dye solution in n-propanol.
All H atoms of the compound were placed in the calculated positions with C—H = 0.93 and 0.97 Å, O—H = 0.82 Å and included in the cycles of
in a rigid model, with Uiso(H) = 1.2 Ueq(C) and 1.5 Ueq(O).A series of azo disperse dyes was recently synthesized by our group in order to study the influence of substituents on the chromatic properties of the dyes (Suesat et al., 2011). We report herein the
of one of these dyes.The molecule of the title compound (Fig. 1) displays an E configuration about the N═N double bond and is not planar, the dihedral angle between the aromatic ring being 7.51 (8)°. This value may be compared with those observed in the related compounds 4'-(dimethylamino)-2-nitroazobenzene (5.3 (2)°; Zhang et al., 1998) and 4'-(dimethylamino)-4-nitroazobenzene (2.1 (4)°; Adams et al., 2004). The nitro group is tilted by 4.71 (11)° with respect to the attached C7–C11 benzene ring. In the molecules are linked by O—H···O hydrogen bonds (Table 1) to form double-stranded chain parallel to the b axis (Fig. 2).
For the properties of azo disperse dyes, see: Suesat et al. (2011). For the structure of related compounds, see: Zhang et al. (1998); Adams et al. (2004).
Data collection: APEX2 (Bruker, 2011); cell
SAINT (Bruker, 2011); data reduction: SAINT (Bruker, 2011); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).C16H18N4O4 | F(000) = 696 |
Mr = 330.34 | Dx = 1.419 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 1201 reflections |
a = 19.000 (3) Å | θ = 3.0–21.9° |
b = 7.3502 (16) Å | µ = 0.10 mm−1 |
c = 11.0825 (16) Å | T = 296 K |
β = 92.060 (8)° | Plate, purple |
V = 1546.7 (5) Å3 | 0.24 × 0.16 × 0.04 mm |
Z = 4 |
Bruker APEXII CCD diffractometer | 1642 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.032 |
Graphite monochromator | θmax = 25.1°, θmin = 1.1° |
φ and ω scans | h = −22→22 |
7008 measured reflections | k = −8→7 |
2671 independent reflections | l = −13→12 |
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)] = 0.044 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.152 | H-atom parameters constrained |
S = 0.93 | w = 1/[σ2(Fo2) + (0.096P)2] where P = (Fo2 + 2Fc2)/3 |
2671 reflections | (Δ/σ)max < 0.001 |
219 parameters | Δρmax = 0.17 e Å−3 |
0 restraints | Δρmin = −0.19 e Å−3 |
C16H18N4O4 | V = 1546.7 (5) Å3 |
Mr = 330.34 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 19.000 (3) Å | µ = 0.10 mm−1 |
b = 7.3502 (16) Å | T = 296 K |
c = 11.0825 (16) Å | 0.24 × 0.16 × 0.04 mm |
β = 92.060 (8)° |
Bruker APEXII CCD diffractometer | 1642 reflections with I > 2σ(I) |
7008 measured reflections | Rint = 0.032 |
2671 independent reflections |
R[F2 > 2σ(F2)] = 0.044 | 0 restraints |
wR(F2) = 0.152 | H-atom parameters constrained |
S = 0.93 | Δρmax = 0.17 e Å−3 |
2671 reflections | Δρmin = −0.19 e Å−3 |
219 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.05195 (11) | 0.8516 (3) | 0.17672 (18) | 0.0594 (6) | |
H1 | 0.0644 | 0.9565 | 0.1905 | 0.089* | |
O2 | 0.76929 (9) | 0.9038 (3) | −0.02037 (17) | 0.0597 (6) | |
O3 | 0.74369 (9) | 0.9967 (3) | −0.20053 (17) | 0.0586 (6) | |
O4 | 0.06568 (10) | 0.2095 (3) | 0.22729 (19) | 0.0633 (6) | |
H4 | 0.0285 | 0.2525 | 0.2496 | 0.095* | |
N1 | 0.14613 (9) | 0.5386 (3) | 0.14546 (17) | 0.0354 (5) | |
N2 | 0.42757 (9) | 0.6797 (3) | 0.04905 (17) | 0.0365 (5) | |
N3 | 0.44265 (10) | 0.7473 (3) | −0.05171 (17) | 0.0368 (5) | |
N4 | 0.72717 (11) | 0.9329 (3) | −0.1042 (2) | 0.0411 (6) | |
C1 | 0.07605 (14) | 0.7966 (4) | 0.0624 (2) | 0.0497 (8) | |
H1A | 0.1193 | 0.8604 | 0.0453 | 0.060* | |
H1B | 0.0410 | 0.8267 | −0.0003 | 0.060* | |
C2 | 0.08899 (12) | 0.5953 (4) | 0.0634 (2) | 0.0408 (7) | |
H2A | 0.0462 | 0.5340 | 0.0858 | 0.049* | |
H2B | 0.0995 | 0.5566 | −0.0176 | 0.049* | |
C3 | 0.21506 (12) | 0.5627 (3) | 0.1166 (2) | 0.0317 (6) | |
C4 | 0.27042 (12) | 0.5308 (3) | 0.2010 (2) | 0.0367 (6) | |
H4A | 0.2606 | 0.4825 | 0.2761 | 0.044* | |
C5 | 0.33886 (12) | 0.5695 (4) | 0.1749 (2) | 0.0379 (6) | |
H5 | 0.3743 | 0.5498 | 0.2335 | 0.046* | |
C6 | 0.35640 (11) | 0.6375 (3) | 0.06305 (19) | 0.0320 (6) | |
C7 | 0.51515 (12) | 0.7925 (3) | −0.0583 (2) | 0.0332 (6) | |
C8 | 0.56560 (12) | 0.7559 (4) | 0.0318 (2) | 0.0406 (7) | |
H8 | 0.5525 | 0.6992 | 0.1026 | 0.049* | |
C9 | 0.63476 (13) | 0.8029 (4) | 0.0174 (2) | 0.0403 (7) | |
H9 | 0.6687 | 0.7776 | 0.0776 | 0.048* | |
C10 | 0.65295 (11) | 0.8877 (3) | −0.0873 (2) | 0.0328 (6) | |
C11 | 0.53504 (12) | 0.8809 (4) | −0.1621 (2) | 0.0398 (7) | |
H11 | 0.5013 | 0.9080 | −0.2223 | 0.048* | |
C12 | 0.60435 (13) | 0.9292 (4) | −0.1773 (2) | 0.0399 (7) | |
H12 | 0.6177 | 0.9885 | −0.2470 | 0.048* | |
C13 | 0.12743 (13) | 0.4915 (4) | 0.2676 (2) | 0.0400 (6) | |
H13A | 0.0822 | 0.5462 | 0.2834 | 0.048* | |
H13B | 0.1620 | 0.5446 | 0.3236 | 0.048* | |
C14 | 0.12301 (14) | 0.2927 (4) | 0.2926 (3) | 0.0536 (8) | |
H14A | 0.1666 | 0.2347 | 0.2708 | 0.064* | |
H14B | 0.1174 | 0.2741 | 0.3784 | 0.064* | |
C15 | 0.23411 (12) | 0.6236 (4) | 0.0017 (2) | 0.0371 (6) | |
H15 | 0.1991 | 0.6398 | −0.0582 | 0.045* | |
C16 | 0.30250 (12) | 0.6596 (3) | −0.0241 (2) | 0.0353 (6) | |
H16 | 0.3132 | 0.6994 | −0.1010 | 0.042* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0536 (12) | 0.0370 (13) | 0.0894 (15) | −0.0012 (10) | 0.0307 (11) | −0.0022 (10) |
O2 | 0.0321 (11) | 0.0772 (16) | 0.0690 (13) | −0.0058 (10) | −0.0091 (10) | 0.0015 (11) |
O3 | 0.0404 (11) | 0.0767 (16) | 0.0600 (13) | −0.0067 (10) | 0.0176 (9) | 0.0071 (11) |
O4 | 0.0494 (13) | 0.0405 (13) | 0.1017 (16) | −0.0089 (10) | 0.0257 (12) | −0.0144 (11) |
N1 | 0.0246 (10) | 0.0402 (14) | 0.0417 (11) | −0.0018 (9) | 0.0043 (9) | −0.0004 (9) |
N2 | 0.0280 (12) | 0.0409 (14) | 0.0410 (12) | −0.0022 (10) | 0.0065 (9) | −0.0014 (10) |
N3 | 0.0286 (12) | 0.0438 (14) | 0.0380 (12) | −0.0035 (10) | 0.0042 (9) | −0.0029 (10) |
N4 | 0.0296 (12) | 0.0413 (14) | 0.0527 (13) | −0.0019 (10) | 0.0063 (11) | −0.0080 (11) |
C1 | 0.0353 (15) | 0.056 (2) | 0.0587 (17) | 0.0061 (14) | 0.0085 (13) | 0.0114 (14) |
C2 | 0.0262 (13) | 0.0494 (18) | 0.0468 (15) | −0.0054 (12) | 0.0009 (11) | −0.0059 (13) |
C3 | 0.0281 (13) | 0.0275 (14) | 0.0398 (13) | −0.0012 (11) | 0.0041 (10) | −0.0048 (11) |
C4 | 0.0329 (14) | 0.0404 (17) | 0.0370 (13) | −0.0025 (12) | 0.0052 (11) | 0.0026 (11) |
C5 | 0.0284 (13) | 0.0441 (17) | 0.0410 (14) | −0.0009 (12) | −0.0019 (10) | 0.0024 (12) |
C6 | 0.0276 (13) | 0.0323 (15) | 0.0367 (13) | −0.0011 (11) | 0.0066 (10) | −0.0044 (11) |
C7 | 0.0263 (13) | 0.0388 (16) | 0.0346 (13) | −0.0017 (11) | 0.0048 (10) | −0.0064 (11) |
C8 | 0.0349 (15) | 0.0511 (19) | 0.0360 (13) | −0.0032 (13) | 0.0040 (11) | 0.0072 (12) |
C9 | 0.0316 (14) | 0.0484 (18) | 0.0406 (14) | −0.0008 (12) | −0.0034 (11) | 0.0018 (12) |
C10 | 0.0252 (12) | 0.0348 (15) | 0.0386 (14) | −0.0001 (11) | 0.0053 (10) | −0.0076 (11) |
C11 | 0.0306 (14) | 0.0571 (19) | 0.0318 (13) | 0.0000 (13) | 0.0004 (10) | −0.0003 (12) |
C12 | 0.0379 (14) | 0.0500 (18) | 0.0323 (13) | −0.0045 (13) | 0.0074 (11) | 0.0006 (12) |
C13 | 0.0287 (13) | 0.0439 (17) | 0.0479 (15) | −0.0041 (12) | 0.0095 (11) | −0.0005 (12) |
C14 | 0.0384 (16) | 0.0450 (19) | 0.0784 (19) | −0.0011 (14) | 0.0154 (14) | 0.0106 (15) |
C15 | 0.0303 (13) | 0.0440 (17) | 0.0368 (13) | −0.0008 (12) | −0.0006 (10) | −0.0012 (11) |
C16 | 0.0332 (14) | 0.0400 (16) | 0.0331 (12) | 0.0016 (12) | 0.0058 (11) | −0.0006 (11) |
O1—C1 | 1.421 (3) | C5—C6 | 1.389 (3) |
O1—H1 | 0.8200 | C5—H5 | 0.9300 |
O2—N4 | 1.224 (3) | C6—C16 | 1.392 (3) |
O3—N4 | 1.217 (2) | C7—C11 | 1.386 (3) |
O4—C14 | 1.424 (3) | C7—C8 | 1.386 (3) |
O4—H4 | 0.8200 | C8—C9 | 1.373 (3) |
N1—C3 | 1.371 (3) | C8—H8 | 0.9300 |
N1—C2 | 1.452 (3) | C9—C10 | 1.373 (3) |
N1—C13 | 1.454 (3) | C9—H9 | 0.9300 |
N2—N3 | 1.265 (3) | C10—C12 | 1.369 (3) |
N2—C6 | 1.401 (3) | C11—C12 | 1.380 (3) |
N3—C7 | 1.422 (3) | C11—H11 | 0.9300 |
N4—C10 | 1.467 (3) | C12—H12 | 0.9300 |
C1—C2 | 1.500 (4) | C13—C14 | 1.490 (4) |
C1—H1A | 0.9700 | C13—H13A | 0.9700 |
C1—H1B | 0.9700 | C13—H13B | 0.9700 |
C2—H2A | 0.9700 | C14—H14A | 0.9700 |
C2—H2B | 0.9700 | C14—H14B | 0.9700 |
C3—C4 | 1.403 (3) | C15—C16 | 1.367 (3) |
C3—C15 | 1.409 (3) | C15—H15 | 0.9300 |
C4—C5 | 1.372 (3) | C16—H16 | 0.9300 |
C4—H4A | 0.9300 | ||
C1—O1—H1 | 109.5 | C11—C7—N3 | 116.5 (2) |
C14—O4—H4 | 109.5 | C8—C7—N3 | 124.3 (2) |
C3—N1—C2 | 121.05 (19) | C9—C8—C7 | 120.5 (2) |
C3—N1—C13 | 121.1 (2) | C9—C8—H8 | 119.8 |
C2—N1—C13 | 116.69 (18) | C7—C8—H8 | 119.8 |
N3—N2—C6 | 115.78 (19) | C10—C9—C8 | 118.9 (2) |
N2—N3—C7 | 112.83 (19) | C10—C9—H9 | 120.5 |
O3—N4—O2 | 123.5 (2) | C8—C9—H9 | 120.5 |
O3—N4—C10 | 118.6 (2) | C12—C10—C9 | 122.2 (2) |
O2—N4—C10 | 118.0 (2) | C12—C10—N4 | 118.9 (2) |
O1—C1—C2 | 109.4 (2) | C9—C10—N4 | 118.9 (2) |
O1—C1—H1A | 109.8 | C12—C11—C7 | 120.8 (2) |
C2—C1—H1A | 109.8 | C12—C11—H11 | 119.6 |
O1—C1—H1B | 109.8 | C7—C11—H11 | 119.6 |
C2—C1—H1B | 109.8 | C10—C12—C11 | 118.4 (2) |
H1A—C1—H1B | 108.2 | C10—C12—H12 | 120.8 |
N1—C2—C1 | 114.0 (2) | C11—C12—H12 | 120.8 |
N1—C2—H2A | 108.8 | N1—C13—C14 | 115.1 (2) |
C1—C2—H2A | 108.8 | N1—C13—H13A | 108.5 |
N1—C2—H2B | 108.8 | C14—C13—H13A | 108.5 |
C1—C2—H2B | 108.8 | N1—C13—H13B | 108.5 |
H2A—C2—H2B | 107.7 | C14—C13—H13B | 108.5 |
N1—C3—C4 | 121.5 (2) | H13A—C13—H13B | 107.5 |
N1—C3—C15 | 122.1 (2) | O4—C14—C13 | 111.9 (2) |
C4—C3—C15 | 116.4 (2) | O4—C14—H14A | 109.2 |
C5—C4—C3 | 121.2 (2) | C13—C14—H14A | 109.2 |
C5—C4—H4A | 119.4 | O4—C14—H14B | 109.2 |
C3—C4—H4A | 119.4 | C13—C14—H14B | 109.2 |
C4—C5—C6 | 121.5 (2) | H14A—C14—H14B | 107.9 |
C4—C5—H5 | 119.2 | C16—C15—C3 | 121.9 (2) |
C6—C5—H5 | 119.2 | C16—C15—H15 | 119.1 |
C5—C6—C16 | 117.9 (2) | C3—C15—H15 | 119.1 |
C5—C6—N2 | 116.2 (2) | C15—C16—C6 | 120.9 (2) |
C16—C6—N2 | 125.9 (2) | C15—C16—H16 | 119.6 |
C11—C7—C8 | 119.2 (2) | C6—C16—H16 | 119.6 |
C6—N2—N3—C7 | 178.01 (19) | C8—C9—C10—C12 | 0.8 (4) |
C3—N1—C2—C1 | −76.6 (3) | C8—C9—C10—N4 | −178.2 (2) |
C13—N1—C2—C1 | 91.0 (3) | O3—N4—C10—C12 | −4.0 (3) |
O1—C1—C2—N1 | −65.8 (3) | O2—N4—C10—C12 | 176.2 (2) |
C2—N1—C3—C4 | 171.5 (2) | O3—N4—C10—C9 | 175.0 (2) |
C13—N1—C3—C4 | 4.5 (3) | O2—N4—C10—C9 | −4.8 (3) |
C2—N1—C3—C15 | −7.4 (3) | C8—C7—C11—C12 | 1.3 (4) |
C13—N1—C3—C15 | −174.4 (2) | N3—C7—C11—C12 | −179.5 (2) |
N1—C3—C4—C5 | −174.5 (2) | C9—C10—C12—C11 | −1.1 (4) |
C15—C3—C4—C5 | 4.4 (3) | N4—C10—C12—C11 | 178.0 (2) |
C3—C4—C5—C6 | −1.6 (4) | C7—C11—C12—C10 | 0.0 (4) |
C4—C5—C6—C16 | −2.2 (4) | C3—N1—C13—C14 | −90.9 (3) |
C4—C5—C6—N2 | 177.1 (2) | C2—N1—C13—C14 | 101.5 (3) |
N3—N2—C6—C5 | −177.7 (2) | N1—C13—C14—O4 | −67.5 (3) |
N3—N2—C6—C16 | 1.5 (4) | N1—C3—C15—C16 | 175.4 (2) |
N2—N3—C7—C11 | −174.9 (2) | C4—C3—C15—C16 | −3.6 (4) |
N2—N3—C7—C8 | 4.2 (3) | C3—C15—C16—C6 | −0.1 (4) |
C11—C7—C8—C9 | −1.5 (4) | C5—C6—C16—C15 | 3.0 (4) |
N3—C7—C8—C9 | 179.4 (2) | N2—C6—C16—C15 | −176.2 (2) |
C7—C8—C9—C10 | 0.5 (4) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···O4i | 0.82 | 1.90 | 2.700 (3) | 164 |
O4—H4···O1ii | 0.82 | 1.90 | 2.718 (3) | 172 |
Symmetry codes: (i) x, y+1, z; (ii) −x, y−1/2, −z+1/2. |
Experimental details
Crystal data | |
Chemical formula | C16H18N4O4 |
Mr | 330.34 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 296 |
a, b, c (Å) | 19.000 (3), 7.3502 (16), 11.0825 (16) |
β (°) | 92.060 (8) |
V (Å3) | 1546.7 (5) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.10 |
Crystal size (mm) | 0.24 × 0.16 × 0.04 |
Data collection | |
Diffractometer | Bruker APEXII CCD |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7008, 2671, 1642 |
Rint | 0.032 |
(sin θ/λ)max (Å−1) | 0.597 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.044, 0.152, 0.93 |
No. of reflections | 2671 |
No. of parameters | 219 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.17, −0.19 |
Computer programs: APEX2 (Bruker, 2011), SAINT (Bruker, 2011), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···O4i | 0.820 | 1.904 | 2.700 (3) | 163.8 |
O4—H4···O1ii | 0.820 | 1.904 | 2.718 (3) | 172.0 |
Symmetry codes: (i) x, y+1, z; (ii) −x, y−1/2, −z+1/2. |
Acknowledgements
The authors thank the Kasetsart University Research and Development Institute and the Department of Chemistry, Faculty of Science, Kasetsart University, for research funds.
References
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A series of azo disperse dyes was recently synthesized by our group in order to study the influence of substituents on the chromatic properties of the dyes (Suesat et al., 2011). We report herein the crystal structure of one of these dyes.
The molecule of the title compound (Fig. 1) displays an E configuration about the N═N double bond and is not planar, the dihedral angle between the aromatic ring being 7.51 (8)°. This value may be compared with those observed in the related compounds 4'-(dimethylamino)-2-nitroazobenzene (5.3 (2)°; Zhang et al., 1998) and 4'-(dimethylamino)-4-nitroazobenzene (2.1 (4)°; Adams et al., 2004). The nitro group is tilted by 4.71 (11)° with respect to the attached C7–C11 benzene ring. In the crystal structure, molecules are linked by O—H···O hydrogen bonds (Table 1) to form double-stranded chain parallel to the b axis (Fig. 2).