2,6-Di­methyl-4-(phenyl­diazenyl)­phenol

The crystal structure of the title compound, C₁₄H₁₄N₂O, determined at 293 K, shows that the mol­ecule is approximately planar in the solid state and that the aromatic rings have a trans configuration with respect to the azo double bond, as found for other diazene derivatives. The packing can be described as a polymeric arrangement of mol­ecules linked through O-H...N and C-H...O hydrogen bonds and close contacts. These intermolecular interactions result in the formation of infinite chains parallel to the b axis.

S1. Comment

Diazenes have been widely used as dyes, owing to their versatility in various fields and in high technologies, including textiles, plastics, biological staining, lasers, liquid crystalline displays, electro-optical devices and ink-jet printers (Catino et al., 1985; Gregory, 1991). Because of their wide use, diazenes have been the subject of many experimental studies (Huang et al., 2002; Zhang et al., 1998; Kocaokutgen, Gür et al., 2003; Kocaokutgen, Soylu et al., 2003). In this paper, we report the synthesis and crystal structure of the title compound, (I), recrystallized from ethanol. We also include here a comparison of the present structure discussion with those of other diazenes, namely 2,6-dimethyl-4-(4-chlorophenyldiazenyl)phenol, (II) (Kocaokutgen, Gür et al., 2003), and 2-tert-butyl-4-methyl-6-(phenyldiazenyl)phenol, (III) (Kocaokutgen, Soylu et al., 2003). Please check that the two (Kocaokutgen et al., 2003) references have been correctly distinguished. \sch

The structure of (I) is very similar to those of diazene (azo) compounds reported previously. The molecule consists of two aromatic groups, linked through a diazene bridge. The dihedral angles between the azo bridge A (C1—N1═N2—C7) and the coplanar substituted and unsubstituted phenyl rings B (C1—C6) and C (C7—C12) are A/B 13.48 (22), A/C 10.90 (21) and B/C 6.57 (15)°, i.e. the two substituted phenyl rings are approximately coplanar. Some related torsion angles are reported in Table 1. The aromatic rings are in a trans configuration with respect to the azo double bond. The N1—C1 and N2—C7 bond lengths of 1.451 (3) and 1.428 (3) Å, respectively, indicate single-bond character, and the N═N bond length of 1.252 (3) Å is indicative of significant double-bond character.

In the structure of (I), the hydroxyl group forms two close intermolecular contacts with a symmetry-related molecule (Table 2). In the first interaction, the hydroxyl group (atom O1) serves as a hydrogen-bond donor to one of the azo-N atoms in a neighbouring molecule and in the second, it is in close contact with the H atom bonded to atom C8 of the phenyl ring of the same molecule. These intermolecular interactions link neighbouring molecules in one dimension and are highly effective in forming polymeric chains which stabilize the crystal structure (Fig. 2). As shown in Fig. 2, the chains extend parallel to the b axis.

A comparison of bond lengths and angles associated with the azo group is given in Table 3 for structures (I), (II) and (III). A general conclusion is that the molecular geometry of the diazene moiety of (III) is significantly different from that of (I) and (II). The C—N bond lengths of (I) and (II) are longer than the corresponding values reported for (III), while their N═N bond lengths are shorter. In the chemical structure of (III), there is a hydroxyl group ortho to the azo group which forms an intramolecular hydrogen bond to the distal N atom. We believe that the presence of this intramolecular hydrogen bond is related to the relative expansion of the diazene N═N double bond observed for (III).

The results obtained in this study indicate that there are also significant differences when comparing the molecular structures of (I) and (II). In the previously reported structure of (II), the crystal packing is mainly stabilized by intermolecular O—H···O hydrogen bonds, which form a dimeric arrangement. From the results presented in this paper, it can be said that the crystal is stabilized by a seven-membered chelate ring via O—H···N hydrogen bonds and close C—H···O interactions, which are highly effective in forming polymeric chains in one dimension (Fig. 2). Dipole-dipole and van der Waals interactions are also effective in the molecular packing in the crystal structure.

S2. Experimental

A mixture of aniline (0.02 mol), water (40 ml) and concentrated hydrochloric acid (0.06 mol) was stirred. This solution was cooled to 273–278 K and a solution of sodium nitrite (0.02 mol) in water (10 ml) was then added dropwise, while maintaining the temperature below 278 K. The resulting mixture was stirred for an additional 30 min in an ice bath and then buffered with solid sodium acetate. 2.6-Dimethylphenol (0.02 mol), dissolved with sodium hydroxide (0.02 mol) in water (10 ml), was cooled to 273–278 K in an ice bath and then gradually added to the above solution of benzendiazonium chloride. The resulting mixture was stirred for 60 min. The crude precipitate was filtered, washed several times with water and recrystallized from ethanol to give a product of m.p. 364–365 K; yield 86%. Its purity was monitored by thin-layer chromatography. The compound was recrystallized from ethanol to produce crystals of (I) of suitable quality for X-ray diffraction analysis. The IR spectrum of (I) was recorded using an IASCO FT/IR-430 spectrophotometer. IR spectroscopic data (ν, cm⁻¹): 3350 (O—H), 2953–2920 (CH₃). Elemental analysis, calculated: C 74.34, H 6.19, N 12.39; found: C 74.28, H 6.35, N 12.03. UV-vis measurements [λ (nm), log ε (mol⁻¹ cm⁻¹ Please check), CH₃CH₂OH]: 353 (4.713), 444 (3.454). ¹H NMR (200 MHz, DMSO-d₆, δ, p.p.m.): 8.98 (S, H, OH), 740–7.85 (m, 7H, Ar), 2.29 (S, 3H, CH₃).

S3. Refinement

H atoms were placed in calculated positions.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT; program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. A drawing of the molecule of (I), with 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. Diagram of the hydrogen-bonding interactions in (I) (dashed lines). Displacement ellipsoids are drawn at the 30% probability level. [Symmetry code: (i) 2 − x, y − 1/2, 3/2 − z.]

2,6-Dimethyl-4-(phenyldiazenyl)phenol

Crystal data

C14H14N2O	F(000) = 480
Mr = 226.27	Dx = 1.245 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.1447 (16) Å	Cell parameters from 12915 reflections
b = 10.7602 (14) Å	θ = 2.7–28.3°
c = 10.5103 (15) Å	µ = 0.08 mm^−1
β = 106.775 (2)°	T = 210 K
V = 1206.8 (3) Å^3	Prism, orange
Z = 4	0.30 × 0.30 × 0.10 mm

Data collection

Bruker SMART CCD area-detector diffractometer	2896 independent reflections
Radiation source: fine-focus sealed tube	2063 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.042
ω scans	θmax = 28.3°, θmin = 2.7°
Absorption correction: multi-scan (SADABS; Bruker, 1998)	h = −8→14
Tmin = 0.976, Tmax = 0.992	k = −8→14
4421 measured reflections	l = −13→13

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)] = 0.069	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.170	All H-atom parameters refined
S = 1.09	w = 1/[σ^2(Fo^2) + (0.0606P)^2 + 0.6654P] where P = (Fo^2 + 2Fc^2)/3
2896 reflections	(Δ/σ)max < 0.001
210 parameters	Δρmax = 0.27 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
O1	1.08315 (15)	−0.21572 (15)	0.60875 (17)	0.0414 (4)
N1	0.70110 (16)	0.18713 (18)	0.67830 (18)	0.0381 (4)
N2	0.68674 (17)	0.10030 (18)	0.59602 (18)	0.0389 (4)
C1	0.59182 (18)	0.2669 (2)	0.6534 (2)	0.0360 (5)
C2	0.5922 (2)	0.3495 (2)	0.7534 (2)	0.0445 (6)
C3	0.4954 (2)	0.4333 (3)	0.7387 (3)	0.0487 (6)
C4	0.3981 (2)	0.4369 (3)	0.6218 (3)	0.0486 (6)
C5	0.3976 (2)	0.3530 (3)	0.5225 (3)	0.0557 (7)
C6	0.4932 (2)	0.2674 (3)	0.5371 (3)	0.0481 (6)
C7	0.79281 (19)	0.0208 (2)	0.6126 (2)	0.0370 (5)
C8	0.9006 (2)	0.0203 (2)	0.7221 (2)	0.0375 (5)
C9	0.99993 (19)	−0.0584 (2)	0.7249 (2)	0.0358 (5)
C10	0.98975 (19)	−0.13727 (19)	0.6164 (2)	0.0336 (5)
C11	0.8814 (2)	−0.1394 (2)	0.5069 (2)	0.0368 (5)
C12	0.7843 (2)	−0.0609 (2)	0.5086 (2)	0.0383 (5)
C13	1.1162 (2)	−0.0591 (3)	0.8422 (3)	0.0501 (7)
C14	0.8736 (3)	−0.2254 (3)	0.3927 (3)	0.0486 (6)
H1O	1.135 (3)	−0.224 (3)	0.680 (3)	0.076 (11)*
H2	0.664 (3)	0.347 (3)	0.833 (3)	0.070 (9)*
H3	0.493 (3)	0.489 (3)	0.806 (3)	0.058 (8)*
H4	0.327 (3)	0.498 (3)	0.611 (3)	0.059 (8)*
H5	0.336 (3)	0.353 (3)	0.443 (3)	0.066 (9)*
H6	0.491 (2)	0.216 (3)	0.468 (3)	0.056 (8)*
H8	0.910 (2)	0.069 (2)	0.797 (2)	0.039 (6)*
H12	0.706 (2)	−0.058 (2)	0.437 (3)	0.052 (7)*
H13A	1.196 (3)	−0.043 (2)	0.813 (3)	0.051 (7)*
H13B	1.131 (3)	−0.140 (3)	0.891 (3)	0.067 (9)*
H13C	1.110 (3)	0.005 (3)	0.911 (3)	0.075 (9)*
H14A	0.791 (3)	−0.221 (3)	0.328 (3)	0.066 (8)*
H14B	0.887 (3)	−0.317 (3)	0.424 (3)	0.066 (8)*
H14C	0.937 (3)	−0.205 (3)	0.347 (3)	0.076 (10)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0354 (8)	0.0370 (9)	0.0471 (9)	0.0075 (7)	0.0043 (7)	−0.0019 (7)
N1	0.0347 (9)	0.0389 (11)	0.0391 (10)	−0.0027 (8)	0.0082 (7)	−0.0009 (8)
N2	0.0357 (9)	0.0399 (10)	0.0387 (9)	−0.0016 (8)	0.0068 (7)	0.0010 (8)
C1	0.0279 (10)	0.0348 (12)	0.0453 (12)	0.0031 (9)	0.0108 (8)	0.0055 (9)
C2	0.0327 (11)	0.0525 (15)	0.0444 (13)	0.0058 (11)	0.0050 (9)	−0.0054 (11)
C3	0.0369 (12)	0.0520 (15)	0.0542 (14)	0.0048 (11)	0.0084 (10)	−0.0117 (12)
C4	0.0335 (12)	0.0497 (15)	0.0591 (15)	0.0127 (11)	0.0080 (10)	0.0000 (12)
C5	0.0421 (13)	0.0662 (18)	0.0495 (14)	0.0143 (13)	−0.0017 (11)	−0.0027 (13)
C6	0.0429 (13)	0.0521 (15)	0.0449 (13)	0.0059 (11)	0.0057 (10)	−0.0096 (12)
C7	0.0295 (10)	0.0341 (12)	0.0468 (12)	0.0026 (9)	0.0099 (9)	0.0088 (10)
C8	0.0368 (11)	0.0329 (12)	0.0421 (12)	−0.0015 (9)	0.0100 (9)	−0.0009 (10)
C9	0.0310 (10)	0.0302 (11)	0.0434 (12)	−0.0032 (9)	0.0064 (9)	0.0007 (9)
C10	0.0297 (10)	0.0272 (10)	0.0430 (11)	0.0004 (8)	0.0090 (8)	0.0055 (9)
C11	0.0357 (11)	0.0313 (11)	0.0407 (11)	−0.0012 (9)	0.0068 (9)	0.0048 (9)
C12	0.0332 (11)	0.0364 (12)	0.0409 (12)	0.0012 (9)	0.0035 (9)	0.0034 (10)
C13	0.0376 (12)	0.0510 (16)	0.0534 (15)	0.0045 (12)	−0.0004 (11)	−0.0098 (13)
C14	0.0474 (14)	0.0501 (16)	0.0421 (13)	0.0033 (12)	0.0032 (11)	−0.0030 (11)

Geometric parameters (Å, º)

O1—C10	1.360 (3)	C7—C12	1.384 (3)
O1—H1O	0.81 (3)	C7—C8	1.403 (3)
N1—N2	1.252 (3)	C8—C9	1.387 (3)
N1—C1	1.451 (3)	C8—H8	0.93 (2)
N2—C7	1.428 (3)	C9—C10	1.400 (3)
C1—C2	1.375 (3)	C9—C13	1.509 (3)
C1—C6	1.388 (3)	C10—C11	1.407 (3)
C2—C3	1.381 (3)	C11—C12	1.378 (3)
C2—H2	0.97 (3)	C11—C14	1.498 (3)
C3—C4	1.385 (3)	C12—H12	0.97 (3)
C3—H3	0.93 (3)	C13—H13A	1.03 (3)
C4—C5	1.379 (4)	C13—H13B	1.00 (3)
C4—H4	1.01 (3)	C13—H13C	1.01 (3)
C5—C6	1.383 (4)	C14—H14A	0.98 (3)
C5—H5	0.91 (3)	C14—H14B	1.03 (3)
C6—H6	0.91 (3)	C14—H14C	0.99 (3)
C10—O1—H1O	112 (2)	C7—C8—H8	123.7 (14)
N2—N1—C1	112.58 (17)	C8—C9—C10	118.43 (19)
N1—N2—C7	115.25 (18)	C8—C9—C13	120.8 (2)
C2—C1—C6	119.9 (2)	C10—C9—C13	120.8 (2)
C2—C1—N1	115.28 (18)	O1—C10—C9	122.74 (18)
C6—C1—N1	124.8 (2)	O1—C10—C11	115.58 (19)
C1—C2—C3	120.4 (2)	C9—C10—C11	121.67 (19)
C1—C2—H2	117.4 (18)	C12—C11—C10	118.1 (2)
C3—C2—H2	122.2 (18)	C12—C11—C14	121.7 (2)
C2—C3—C4	120.3 (2)	C10—C11—C14	120.2 (2)
C2—C3—H3	121.7 (18)	C11—C12—C7	121.6 (2)
C4—C3—H3	118.0 (18)	C11—C12—H12	122.4 (16)
C5—C4—C3	119.0 (2)	C7—C12—H12	116.0 (16)
C5—C4—H4	120.4 (16)	C9—C13—H13A	111.4 (15)
C3—C4—H4	120.5 (16)	C9—C13—H13B	113.7 (17)
C4—C5—C6	121.2 (2)	H13A—C13—H13B	105 (2)
C4—C5—H5	121.7 (19)	C9—C13—H13C	111.3 (18)
C6—C5—H5	117.1 (19)	H13A—C13—H13C	110 (2)
C5—C6—C1	119.3 (2)	H13B—C13—H13C	105 (2)
C5—C6—H6	118.7 (17)	C11—C14—H14A	110.4 (17)
C1—C6—H6	122.0 (17)	C11—C14—H14B	111.1 (16)
C12—C7—C8	119.5 (2)	H14A—C14—H14B	107 (2)
C12—C7—N2	114.72 (19)	C11—C14—H14C	111.5 (19)
C8—C7—N2	125.8 (2)	H14A—C14—H14C	109 (2)
C9—C8—C7	120.6 (2)	H14B—C14—H14C	108 (3)
C9—C8—H8	115.7 (14)
C1—N1—N2—C7	177.99 (18)	C7—C8—C9—C10	−0.2 (3)
N2—N1—C1—C2	168.4 (2)	C7—C8—C9—C13	179.8 (2)
N2—N1—C1—C6	−13.9 (3)	C8—C9—C10—O1	178.5 (2)
C6—C1—C2—C3	−0.3 (4)	C13—C9—C10—O1	−1.5 (3)
N1—C1—C2—C3	177.5 (2)	C8—C9—C10—C11	−0.9 (3)
C1—C2—C3—C4	−1.4 (4)	C13—C9—C10—C11	179.1 (2)
C2—C3—C4—C5	2.0 (4)	O1—C10—C11—C12	−179.32 (19)
C3—C4—C5—C6	−1.0 (4)	C9—C10—C11—C12	0.2 (3)
C4—C5—C6—C1	−0.6 (4)	O1—C10—C11—C14	0.7 (3)
C2—C1—C6—C5	1.2 (4)	C9—C10—C11—C14	−179.8 (2)
N1—C1—C6—C5	−176.3 (2)	C10—C11—C12—C7	1.8 (3)
N1—N2—C7—C12	−169.24 (19)	C14—C11—C12—C7	−178.3 (2)
N1—N2—C7—C8	10.5 (3)	C8—C7—C12—C11	−2.9 (3)
C12—C7—C8—C9	2.1 (3)	N2—C7—C12—C11	176.9 (2)
N2—C7—C8—C9	−177.7 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···N1^i	0.81 (3)	2.21 (3)	2.963 (2)	155 (3)
C8—H8···O1^ii	0.93 (2)	2.51 (3)	3.328 (3)	147.4 (19)

Symmetry codes: (i) −x+2, y−1/2, −z+3/2; (ii) −x+2, y+1/2, −z+3/2.