2-(4-Methoxyphenyl­azo)-4-phenyl­phenol

The crystal structure of the title compound, C₁₉H₁₆N₂O₂, displays a trans configuration of the azo moiety, which forms an intramolecular O—H...N=N hydrogen bond. The H...N and O...N distances are 1.81 (3) and 2.581 (4) Å, respectively. The azo­benzene moiety is approximately planar, and has a dihedral angle of ca 23° with the substituted phenyl group.

S1. Comment

The extensive application of azo dyes in industry and in analytical determinations has attracted the attention for decades. Some arylazo compounds derived from resorcinol or β-naphtol have widely been used in spectrophotometric determination of metal traces (Betteridge & John, 1973; Pollard et al., 1959). Furthermore, the tautomeric hydroxyazoquinone-hydrazone equilibrium has been evidenced for this kind of compound (Stoyanov & Antonov, 1988; Antonov et al., 1994; Antonov et al., 1995; Antonov & Stoyanov, 1995; Buncel & Keum, 1983). The existence of intramolecular hydrogen bond is of particular interest (Antonov & Stoyanov, 1995). Currently, we are developing a series of novel arylazo dyes derived from 4-phenylphenol in order to investigate the tautomeric equilibrium in solution. X-ray structure analysis of the title compound, (I), has been carried out to observe the conformation of the molecule in the crystals.

The molecular structure is shown in Fig. 1 with atom-numbering scheme. The compound is constituted by phenyl rings A (C1 to C6), B (C11 to C16), C (C17 to C22) and the azo frame D (C1—N1—N2—C12). The phenyl rings A and B adopt a trans configuration about azo functional group, as observed in crystals of the other azo compounds. The dihedral angle between A and B is 2.7 (2)°, which is less than those of 3-tert-butyl-2'-chloro-2-hydroxy-5-methylazobenzene, (I), [5.85° (Isik, Aygün, Kocaokutgen & Tahir, 1998)] and 2-hydroxy-5-tert-butylazobenzene, (II) (3.4°; Candan et al., 1999). The phenyl-azo-benzene frame (A—D—B) is practically planar [shifts of the atoms from the best plane are less than 0.0341 (2) Å], as observed in the crystals of 3-tert-butyl-2-hydroxy-5-methoxyazobenzene, (III) (Isik, Aygün, Kocaokutgen, Tahir et al., 1998). The dihedral angles of the C ring with the ring B and azo frame D are 24.2 (2) and 22.5 (2)°, respectively.

The N1═N2 bond distance is 1.275 (2) Å (Table 1), which is longer than those observed in the azo compounds without intramolecular hydrogen bonds, 2-hydroxy-5-{[4-(2-pyridinylamino)sulfonyl]phenyl}azo)benzoic acid [1.223 (7) Å; van der Sluis & Spek, 1990], and 5'-allyl-2'-benzoyloxy-3'-methoxy-4-nitroazobenzene [1.241 (3) Å; Isik et al., 2000]. The lengthened N═N distance of (I) caused by the intramolecular hydrogen bond (Table 2) with the ortho hydroxyl group in the aromatic moiety is essentially identical to that of (III), 1.274 (3) Å, and a little longer than those of (I) and (II), 1.266 (2) and 1.265 (2) Å, respectively. In bis-4-dimethylaminonaphtaleneazo)-4,4'-stilbene, the N═N distance is 1.256 (3) Å (Foitzik et al., 1991). In (I), the C2—H2···N2 close contact [H2···N2, 2.506 (3) Å, C2···N2, 2.762 (4) Å and C2—H2···N2, 95.9 (2)°] may also contribute to the planarity of the molecule.

The intramolecular hydrogen bond in (I) is comprehensible by comparison with another conformer, (Ia), which can be derived from the concerted rotation of the O1—H1 bond of (I) around the C11—O1 axis by 180°. An ab initio calculation of the optimized geometries (Frisch et al., 1993) indicated that the conformer (I) is more stable than (Ia) by 56.4 kJ mol⁻¹ and 42.5 kJ mol⁻¹ at RHF/3–21 G^* and RHF/6–31 G^* levels, respectively.

S2. Experimental

The title compound was prepared by azoic copulation of 4-methoxyphenyldiazonium salt (0.022 mol of p-anisidine and 0.025 mol of sodium nitrite in strong acidic aqueous solution) with an alkaline aqueous solution of 4-phenylphenol (0.021 mol). After chromatographic purification (hexane-ethyl acetate 70:30 in SiO₂ 230–400 mesh), the crystals were grown by slow evaporation of the solution at room temperature, m.p. 396–399 K.

Computing details

Data collection: XSCANS (Siemens, 1994); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXTL/PC (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL/PC; software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. A view of (I) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

4-phenyl-2-[4-Methoxyphenyldiazenyl]phenol

Crystal data

C19H16N2O2	F(000) = 640
Mr = 304.34	Dx = 1.277 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 6.449 (2) Å	Cell parameters from 49 reflections
b = 8.638 (2) Å	θ = 4.9–24.5°
c = 28.414 (17) Å	µ = 0.08 mm^−1
β = 90.48 (4)°	T = 273 K
V = 1582.9 (1) Å^3	Prism, red
Z = 4	0.40 × 0.24 × 0.20 mm

Data collection

Siemens P4/PC diffractometer	Rint = 0.045
Radiation source: fine-focus sealed tube	θmax = 25.0°, θmin = 2.5°
Graphite monochromator	h = 0→7
ω–2θ scans	k = 0→10
3062 measured reflections	l = −33→33
2794 independent reflections	3 standard reflections every 97 reflections
1126 reflections with I > 2σ(I)	intensity decay: <2%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.048	H-atom parameters constrained
wR(F^2) = 0.127	Calculated w = 1/[s^2(Fo^2) + (0.0488P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.77	(Δ/σ)max < 0.001
2794 reflections	Δρmax = 0.11 e Å^−3
212 parameters	Δρmin = −0.20 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0102 (11)

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	0.4701 (4)	1.0730 (3)	0.09940 (8)	0.0816 (8)
H1	0.397 (5)	1.027 (4)	0.0774 (10)	0.060*
O2	−0.1259 (4)	0.5901 (3)	−0.09131 (8)	0.0879 (8)
N1	0.1696 (4)	0.9116 (3)	0.06438 (8)	0.0623 (7)
N2	0.0578 (4)	0.9241 (3)	0.10099 (8)	0.0621 (7)
C1	0.0790 (5)	0.8262 (4)	0.02666 (9)	0.0564 (8)
C2	−0.1168 (5)	0.7605 (4)	0.02715 (10)	0.0687 (9)
H2	−0.1991	0.7703	0.0537	0.060*
C3	−0.1895 (5)	0.6814 (4)	−0.01111 (11)	0.0687 (9)
H3	−0.3212	0.6376	−0.0104	0.060*
C4	−0.0688 (5)	0.6657 (4)	−0.05120 (10)	0.0668 (9)
C5	0.1256 (5)	0.7332 (4)	−0.05185 (11)	0.0721 (10)
H5	0.2063	0.7247	−0.0787	0.060*
C6	0.2014 (5)	0.8126 (4)	−0.01349 (10)	0.0664 (9)
H6	0.3328	0.8568	−0.0142	0.060*
C7	−0.3243 (6)	0.5205 (5)	−0.09392 (13)	0.0967 (13)
H7A	−0.3265	0.4300	−0.0743	0.060*
H7B	−0.3540	0.4915	−0.1259	0.060*
H7C	−0.4270	0.5927	−0.0833	0.060*
C11	0.3472 (5)	1.0766 (4)	0.13804 (11)	0.0639 (9)
C12	0.1504 (5)	1.0073 (4)	0.13833 (10)	0.0564 (8)
C13	0.0320 (5)	1.0171 (4)	0.17951 (10)	0.0591 (8)
H13	−0.0989	0.9720	0.1796	0.060*
C14	0.1008 (5)	1.0906 (4)	0.21970 (10)	0.0581 (8)
C15	0.3002 (5)	1.1555 (4)	0.21825 (11)	0.0681 (9)
H15	0.3539	1.2031	0.2451	0.060*
C16	0.4183 (5)	1.1504 (4)	0.17804 (11)	0.0737 (10)
H16	0.5480	1.1975	0.1779	0.060*
C17	−0.0285 (5)	1.0970 (4)	0.26296 (9)	0.0539 (7)
C18	−0.1834 (5)	0.9885 (4)	0.27078 (10)	0.0655 (9)
H18	−0.2033	0.9091	0.2491	0.060*
C19	−0.3089 (5)	0.9953 (4)	0.31004 (11)	0.0731 (10)
H19	−0.4110	0.9208	0.3146	0.060*
C20	−0.2823 (5)	1.1124 (4)	0.34225 (11)	0.0713 (9)
H20	−0.3674	1.1181	0.3685	0.060*
C21	−0.1304 (6)	1.2205 (4)	0.33565 (11)	0.0700 (10)
H21	−0.1110	1.2990	0.3577	0.060*
C22	−0.0048 (5)	1.2138 (4)	0.29625 (10)	0.0635 (9)
H22	0.0969	1.2887	0.2920	0.060*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0738 (16)	0.105 (2)	0.0660 (14)	−0.0193 (15)	0.0223 (12)	−0.0006 (14)
O2	0.0790 (17)	0.105 (2)	0.0796 (16)	−0.0001 (16)	0.0076 (13)	−0.0338 (16)
N1	0.0703 (17)	0.0651 (18)	0.0519 (14)	0.0013 (15)	0.0171 (13)	0.0070 (13)
N2	0.0691 (17)	0.0682 (17)	0.0490 (14)	0.0015 (15)	0.0114 (13)	0.0041 (13)
C1	0.066 (2)	0.0552 (19)	0.0479 (17)	0.0025 (17)	0.0133 (15)	0.0057 (14)
C2	0.073 (2)	0.082 (3)	0.0516 (18)	−0.008 (2)	0.0200 (16)	−0.0001 (18)
C3	0.066 (2)	0.074 (2)	0.066 (2)	−0.0054 (19)	0.0157 (17)	0.0047 (18)
C4	0.072 (2)	0.071 (2)	0.0570 (19)	0.010 (2)	0.0065 (17)	−0.0046 (18)
C5	0.067 (2)	0.090 (3)	0.060 (2)	0.005 (2)	0.0212 (17)	−0.0045 (19)
C6	0.061 (2)	0.078 (2)	0.0606 (19)	−0.0022 (19)	0.0152 (16)	0.0025 (18)
C7	0.100 (3)	0.097 (3)	0.094 (3)	−0.003 (3)	−0.005 (2)	−0.021 (2)
C11	0.066 (2)	0.062 (2)	0.0632 (19)	0.0008 (19)	0.0142 (17)	0.0066 (17)
C12	0.059 (2)	0.0587 (19)	0.0519 (17)	0.0017 (17)	0.0055 (15)	0.0042 (15)
C13	0.060 (2)	0.059 (2)	0.0581 (18)	−0.0042 (17)	0.0080 (16)	0.0056 (16)
C14	0.0601 (19)	0.0564 (19)	0.0580 (17)	−0.0014 (17)	0.0046 (15)	0.0057 (16)
C15	0.072 (2)	0.074 (2)	0.0582 (19)	−0.007 (2)	0.0004 (17)	−0.0086 (17)
C16	0.062 (2)	0.087 (3)	0.071 (2)	−0.020 (2)	0.0104 (18)	0.001 (2)
C17	0.0597 (19)	0.0512 (18)	0.0508 (16)	0.0032 (16)	0.0017 (14)	0.0021 (15)
C18	0.078 (2)	0.063 (2)	0.0563 (18)	−0.003 (2)	0.0091 (17)	−0.0094 (16)
C19	0.070 (2)	0.078 (3)	0.072 (2)	−0.009 (2)	0.0158 (18)	−0.0007 (19)
C20	0.076 (2)	0.078 (2)	0.0601 (19)	0.004 (2)	0.0156 (17)	−0.0017 (19)
C21	0.090 (3)	0.063 (2)	0.0572 (18)	0.002 (2)	0.0057 (18)	−0.0079 (16)
C22	0.071 (2)	0.057 (2)	0.0628 (19)	−0.0008 (18)	0.0057 (17)	0.0015 (16)

Geometric parameters (Å, º)

O1—C11	1.361 (4)	C11—C12	1.403 (4)
O1—H1	0.87 (3)	C12—C13	1.405 (4)
O2—C4	1.360 (4)	C13—C14	1.377 (4)
O2—C7	1.414 (4)	C13—H13	0.9300
N1—N2	1.275 (3)	C14—C15	1.405 (4)
N1—C1	1.423 (4)	C14—C17	1.492 (4)
N2—C12	1.409 (4)	C15—C16	1.379 (4)
C1—C2	1.385 (4)	C15—H15	0.9300
C1—C6	1.398 (4)	C16—H16	0.9300
C2—C3	1.365 (4)	C17—C18	1.389 (4)
C2—H2	0.9300	C17—C22	1.391 (4)
C3—C4	1.392 (4)	C18—C19	1.384 (4)
C3—H3	0.9300	C18—H18	0.9300
C4—C5	1.382 (5)	C19—C20	1.374 (5)
C5—C6	1.373 (4)	C19—H19	0.9300
C5—H5	0.9300	C20—C21	1.369 (5)
C6—H6	0.9300	C20—H20	0.9300
C7—H7A	0.9600	C21—C22	1.388 (5)
C7—H7B	0.9600	C21—H21	0.9300
C7—H7C	0.9600	C22—H22	0.9300
C11—C16	1.377 (4)
C11—O1—H1	106 (2)	C11—C12—N2	126.3 (3)
C4—O2—C7	119.2 (3)	C13—C12—N2	115.3 (3)
N2—N1—C1	115.4 (3)	C14—C13—C12	123.1 (3)
N1—N2—C12	114.7 (3)	C14—C13—H13	118.4
C2—C1—C6	119.7 (3)	C12—C13—H13	118.4
C2—C1—N1	124.8 (3)	C13—C14—C15	116.5 (3)
C6—C1—N1	115.4 (3)	C13—C14—C17	121.5 (3)
C3—C2—C1	120.2 (3)	C15—C14—C17	121.9 (3)
C3—C2—H2	119.9	C16—C15—C14	121.7 (3)
C1—C2—H2	119.9	C16—C15—H15	119.2
C2—C3—C4	120.7 (3)	C14—C15—H15	119.2
C2—C3—H3	119.6	C11—C16—C15	120.9 (3)
C4—C3—H3	119.6	C11—C16—H16	119.5
O2—C4—C5	115.6 (3)	C15—C16—H16	119.5
O2—C4—C3	125.6 (3)	C18—C17—C22	117.2 (3)
C5—C4—C3	118.8 (3)	C18—C17—C14	120.9 (3)
C6—C5—C4	121.3 (3)	C22—C17—C14	121.9 (3)
C6—C5—H5	119.4	C19—C18—C17	121.7 (3)
C4—C5—H5	119.4	C19—C18—H18	119.2
C5—C6—C1	119.2 (3)	C17—C18—H18	119.2
C5—C6—H6	120.4	C20—C19—C18	119.9 (4)
C1—C6—H6	120.4	C20—C19—H19	120.1
O2—C7—H7A	109.5	C18—C19—H19	120.1
O2—C7—H7B	109.5	C21—C20—C19	119.8 (3)
H7A—C7—H7B	109.5	C21—C20—H20	120.1
O2—C7—H7C	109.5	C19—C20—H20	120.1
H7A—C7—H7C	109.5	C20—C21—C22	120.3 (3)
H7B—C7—H7C	109.5	C20—C21—H21	119.9
O1—C11—C16	118.8 (3)	C22—C21—H21	119.9
O1—C11—C12	121.8 (3)	C21—C22—C17	121.2 (3)
C16—C11—C12	119.3 (3)	C21—C22—H22	119.4
C11—C12—C13	118.4 (3)	C17—C22—H22	119.4

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···N1	0.88 (3)	1.81 (3)	2.581 (4)	146 (3)