Two azo pigments based on β-naphthol

There has been much discussion in the literature of the azo–hydrazone tautomerism of pigments. All commercial azo pigments with β-naphthol as the coupling compound adopt the hydrazone tautomeric form (Ph—NH—N=C) in the solid state. In contrast, the red pigments 1-[4-(dimethyl­amino)phenyl­diazen­yl]-2-naphthol, C₁₈H₁₇N₃O, (1a), and 1-[4-(di­ethyl­amino)phenyl­diazen­yl]-2-naphthol, C₂₀H₂₁N₃O, (1b), have been reported to be azo tautomers or a mixture of azo and hydrazone tautomers in the solid state. To prove these observations, both compounds were synthesized, recrystallized and their crystal structures redetermined by single-crystal structure analysis. Difference electron-density maps show that the H atoms of the hydroxyl groups are indeed bonded to the O atoms. Nevertheless, a small amount of the hydrazone form seems to be present. Hence, the compounds are close to being `real' azo compounds. Compound (1a) crystallizes with a herring-bone structure and compound (1b) forms a rare double herring-bone structure.

S1. Comment

Azo pigments are widely used for the colouration of coatings, plastics and printing inks, with an annual sales volume of more than one billion Euros (Herbst & Hunger, 2004). In the literature, most azo pigments are drawn with an N═N double bond (1-azo to 4-azo, see Fig. 1). However, all commercial pigments based on β-naphthol adopt the hydrazone tautomeric form in the solid state (1-hydrazone). The same holds true for pigments with naphthol-AS (2), pyrazolone (3) and acetoacetylanilide groups (4), as proven by many X-ray structure determinations of β-naphthol pigments (Guggenberger & Teufer, 1975; Whitaker et al., 1978; Salmen et al., 1988; Olivieri et al., 1989; Diamantis et al., 1992, Gilli et al., 2002), naphthol-AS pigments (Kobelt et al., 1972, 1974; Paulus et al., 1982), pyrazolone pigments (Whitaker, 1995) and acetoacetanilide pigments (Paulus et al., 1983; Gridunova et al., 1991; Barrow et al., 2002, 2003). Consequently, all these pigments should not be called 'azo pigments' but 'hydrazone pigments'.

The preference for the hydrazone tautomeric form can be explained by the fact that generally a C═N double bond is energetically more stable than an N═ N double bond. In the case of β-naphthol and naphthol-AS pigments, the formation of the hydrazone tautomer leads to a partial loss of aromaticity in the naphthalene moiety; but this does not have a major impact on the energy. For acetoacetylanilide (4) the hydrazone form is additionally stabilized by the enhanced conjugation of the π-systems; furthermore, planar molecules can generally be packed more densely in the crystalline state, leading to higher lattice energies.

In solution, azo and hydrazone tautomers exist in an equilibrium depending on temperature, solvent and substitution pattern. The equilibrium in solution has been studied by UV–visible (Traven et al., 1980; Antonov et al., 1995; Antonov & Stoyanov, 1995) and NMR spectroscopy (Chippendale et al., 1999; Lycka et al., 2000; Birkett et al., 2000; Machacek et al., 2000; Alarcon et al., 2004). Solid-state NMR investigations have also been carried out (Chippendale et al.,1981; Olivieri et al.,1989; McGeorge et al., 1996, 1998). Quantum mechanical calculations have been performed (Kuder,1972; Gilli et al., 2005; Hihara et al., 2003; Alarcon et al., 2004). A review with 100 references is given by Mustroph (1987).

The crystal structure of 1-(4-(diethylamino)phenylazo)-2-naphthol (1b) has been determined by single-crystal X-ray analysis (Traven et al., 1985). From the N—N, C—N and C—O bond lengths, they concluded that the compound exists 'in a form intermediate between the boundary structures' of the azo and hydrazone tautomeric forms. The X-ray structure determination of the dimethylamino derivative (1a) in the range 100–295 K has been performed (Gilli et al., 2005), showing that the proton of the hydroxyl group is disordered over two positions with a prevalence of the azo tautomer. The occupancies of the proton in the O—H versus N—H forms were determined to be 79 (1):21 (1).

The compounds (1a) and (1b) are not commercially used, because their pigmentary properties, especially their considerable solubilities, do not fit the requirements for an industrial organic pigment.

We redetermined the crystal structures of (1a) and (1b) by single-crystal X-ray analysis and found that both compounds adopt the azo tautomeric form (see Fig. 2); however, in the difference electron-density plots there is still a tiny electron density at the positions of the N—H protons indicating a very small amount of the hydrazone tautomer (see Fig. 3). In both compounds, an intramolecular N···H—O (or N—H···O, respectively) hydrogen bond is formed.

The crystal structures of (1a) and (1b) are not isotypic. Compound (1a) crystallizes in P2₁/n with four molecules per unit cell. The molecules are essentially planar. They are packed in columns in the [010] direction; within the columns neighbouring molecules are stacked antiparallel and linked by inversion centres (see Fig. 4a, in the Supplementary material). Each column is connected to two opposite neighbouring columns by van der Waals interactions, resulting in a sheet in the (001) direction. The sheets themselves are also arranged antiparallel, resulting in the molecules forming a herringbone pattern. In compound (1b) the molecules are planar except for the methyl groups of the diethylamino fragment which stick out of the plane by nearly 90°. The unit cell of (1b) contains eight molecules. The characteristic features are pairs of antiparallel molecules with the ethyl groups pointing outwards (see Fig. 4b, in the Supplementary material). Between the molecules there is an inversion centre. These pairs of molecules form columns in the [001] direction, with neighbouring pairs being rotated by about 90°.

Kelemen et al. (1982) examined more than 30 compounds in an investigation of azo–hydrazone tautomerism and postulated that in a real azo compound the N═N double bond should have a length of 1.20–1.28 Å. Furthermore, the bond length of N—N single bonds as in hydrazone tautomers should be more than 1.4 Å. According to Harada et al. (1997), in non-disordered azobenzenes the N═N double bond has a length of 1.26–1.27 Å. For compounds (1a) and (1b) we found values of 1.282 (2) and 1.288 (2) Å, respectively, which are slightly larger than the value for an N═N double bond. For the C—N bond, a similar effect is observed. This is another indication that the compounds (1a) and (1b) are mainly, but not exclusively, in the azo tautomeric form, i.e. they are close to being 'real' azo pigments.

Related literature

For related literature, see: Alarcon et al. (2004); Antonov & Stoyanov (1995); Antonov, Stoyanov & Stoyanova (1995); Barrow et al. (2002, 2003); Becker et al. (2001); Birkett et al. (2000); Chippendale et al. (1981, 1999); Diamantis et al. (1992); Gilli et al. (2002, 2005); Gridunova et al. (1991); Guggenberger & Teufer (1975); Harada et al. (1997); Herbst & Hunger (2004); Hihara et al. (2003); Kelemen et al. (1982); Kobelt et al. (1972, 1974); Kuder (1972); Lycka et al. (2000); Machacek et al. (2000); McGeorge et al. (1996, 1998); Mustroph (1987); Olivieri et al. (1989); Paulus (1982); Paulus et al. (1983); Salmen et al. (1988); Traven et al. (1980, 1985); Whitaker (1978, 1995).

S2. Experimental

For the synthesis of (1a), 4-(dimethylamino)aniline was diazotized with NaNO₂ in aqueous HCl and coupled with β-naphthol under basic conditions (Becker et al., 2001). A red powder of (1a) was obtained. IR(KBr): 3049(w), 2966(w), 2925(w), 2894(w), 2866(w), 2358(w), 2341(w), 1990(w), 1890(w), 1683(w), 1652(w), 1596(s), 1558(m), 1515(m), 1506(w), 1467(w), 1402(s), 1375(m), 1352(w), 1344(w), 1313(w), 1272(m), 1245(m), 1193(w), 1164(m), 1153(m), 1135(w), 1080(s), 1010(m), 977(m), 958(w), 918(w), 864(w), 813(s), 783(w), 750(s), 729(w), 676(w), 669(w), 632(w), 565(w), 534(w), 511(w), 459(w), 447(w), 414(w), ¹H-NMR (250 MHz, DMSO, 298 K, TMS): δ = 3.09 (s, 6H, H17A—C, H18A—C), 6.90 (dm, 2H, H13, H15, ³J = 9.3 Hz), 7.21 (d, 1H, H7, ³J = 9.25 Hz), 7.47 (ddd, 1H, H3, ³J1 = 8.0 Hz, ³J2 = 6.9 Hz, ³J3 = 1.2 Hz), 7.64 (ddd, 1H, H2, ³J1 = 8.4 Hz, ³J2 = 6.9 Hz, ³J3 = 1.3 Hz), 7.91 (m, 4H, H4, H6, H12, H16), 8.77 (d, 1H, H1A, ³J = 8.61 Hz), 14.9 (s, 1H, H1); the correlations were proven by COSY experiments.

(1a) was dissolved in boiling benzene and cooled to room temperature. The solvent was slowly evaporated at room temperature. Crystals in the form of red needles up to 2 x 0.32 x 0.25 mm³ were obtained.

The synthesis of (1b) was as described for (1a). A red powder of (1b) was obtained. IR(KBr): 3074(w), 3049(w), 2966(m), 2925(w), 2894(w), 2866(w), 2671(w), 2611(w), 2360(w), 1596(s), 1554(w), 1515(m), 1508(w), 1483(w), 1467(m), 1456(w), 1446(w), 1402(s), 1375(s), 1352(m), 1346(w), 1313(m), 1274(s), 1247(s), 1193(m), 1166(s), 1153(m), 1135(w), 1080(s), 1010(s), 977(m), 958(w), 918(w), 864(w), 813(s), 761(w), 750(s), 729(w), 676(w), 632(s), 565(m), 536(w), 520(m), 459(m), 447(w), 414(m); ¹H-NMR (250 MHz, DMSO, 298 K, TMS): δ = 1.18 (t, 6H, H18A—C, H20A—C, ³J = 7 Hz), 3.49 (q, 4H, H17A—B, H19A—B, ³J = 6.81 Hz), 6.87 (d, 1H, H13, H15, ³J = 8.92), 7.19 (d, 1H, H7, ³J = 8.7 Hz), 7.47 (ddd, 1H, H3, ³J1 = 8.1 Hz, ³J2 = 6.9 Hz, ³J3 = 1.2 Hz), 7.64 (ddd, 1H, H2, ³J1 = 8.3 Hz, ³J2 = 6.8 Hz, ³J3 = 1.3 Hz), 7.91 (m, 4H, H4, H6, H12, H16), 8.77 (d, 1H, H1,³J = 8.34 Hz), 14.88 (s, 1H, H1O); the correlations were proven by COSY experiments.

(1b) was dissolved in boiling acetone and cooled to room temperature. The solvent was slowly evaporated at room temperature. Crystals in the form of red needles up to 0.2 x 0.4 x 0.2 mm³ were obtained.

S3. Refinement

For both compounds, all H atoms were located in a difference map, but those bonded to C were refined with fixed individual displacement parameters [U(H) = 1.2 U_eq(C)] or [U(H) = 1.5 U_eq(C_methyl)] using a riding model with C_aromatic—H = 0.95 Å, C_methyl—H = 0.98 Å and C_methylene—H = 0.99 Å. The methyl groups in (1a) were allowed to rotate but not to tip. The hydroxyl H atoms were refined isotropically.

Computing details

For both compounds, data collection: X-AREA (Stoe & Cie, 2001); cell refinement: X-AREA (Stoe & Cie, 2001); data reduction: X-RED (Stoe & Cie, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and publCIF (Westrip, 2008).

Figures

Fig. 1. The molecular structures of azo pigments based on: β-naphthol (1), naphthol-AS (2), pyrazolone (3) and acetoacetanilide (4). For (1a) and (1b) the azo form is preferred. Fig. 2. Ellipsoid plots of (1a) (a) and (1b) (b). Ellipsoids are drawn at the 50% probability level. Fig. 3. Difference electron-density map of (1a) (a) and (1b) (b). The position of the protons at the hydroxyl groups is clearly visible. Fig. 4. (a) Packing of (1a), view diection [100]. (b) Packing of (1b), view diection [001]; two pairs of molecules are highlighted.

(1a) 1-[4-(dimethylamino)phenyldiazenyl]-2-naphthol

Crystal data

C18H17N3O	F(000) = 616
Mr = 291.35	Dx = 1.304 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 12577 reflections
a = 7.6443 (6) Å	θ = 3.2–28.5°
b = 8.0127 (6) Å	µ = 0.08 mm^−1
c = 24.512 (2) Å	T = 173 K
β = 98.640 (6)°	Rod, black
V = 1484.4 (2) Å^3	0.32 × 0.14 × 0.13 mm
Z = 4

Data collection

Stoe IPDSII two-circle diffractometer	2762 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.082
Graphite monochromator	θmax = 29.6°, θmin = 3.6°
ω scans	h = −10→9
25765 measured reflections	k = −11→11
4153 independent reflections	l = −33→34

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)] = 0.058	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.138	H atoms treated by a mixture of independent and constrained refinement
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0622P)^2 + 0.2854P] where P = (Fo^2 + 2Fc^2)/3
4153 reflections	(Δ/σ)max < 0.001
205 parameters	Δρmax = 0.28 e Å^−3
0 restraints	Δρmin = −0.21 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	0.03506 (16)	0.50773 (19)	0.56917 (5)	0.0414 (3)
H1	0.124 (4)	0.448 (4)	0.5507 (12)	0.088 (9)*
N1	0.41528 (16)	0.44165 (16)	0.59796 (5)	0.0257 (3)
N2	0.33170 (16)	0.39380 (16)	0.55129 (5)	0.0269 (3)
N3	0.68152 (18)	0.03381 (19)	0.40367 (5)	0.0331 (3)
C1	0.5859 (2)	0.5583 (2)	0.70036 (7)	0.0328 (3)
H1A	0.6513	0.4977	0.6769	0.039*
C2	0.6697 (2)	0.6165 (3)	0.75018 (7)	0.0432 (4)
H2	0.7919	0.5937	0.7611	0.052*
C3	0.5763 (3)	0.7099 (3)	0.78547 (8)	0.0448 (5)
H3	0.6356	0.7502	0.8198	0.054*
C4	0.4001 (3)	0.7418 (2)	0.76994 (7)	0.0387 (4)
H4	0.3383	0.8059	0.7935	0.046*
C5	0.3078 (2)	0.6808 (2)	0.71930 (6)	0.0303 (3)
C6	0.1234 (2)	0.7097 (2)	0.70287 (7)	0.0358 (4)
H6	0.0595	0.7718	0.7264	0.043*
C7	0.0371 (2)	0.6501 (2)	0.65415 (7)	0.0370 (4)
H7	−0.0864	0.6692	0.6447	0.044*
C8	0.1285 (2)	0.5597 (2)	0.61717 (6)	0.0305 (3)
C9	0.31105 (19)	0.52865 (18)	0.63135 (6)	0.0255 (3)
C10	0.4024 (2)	0.58772 (19)	0.68341 (6)	0.0269 (3)
C11	0.43021 (19)	0.30679 (18)	0.51625 (6)	0.0252 (3)
C12	0.6134 (2)	0.27770 (19)	0.52718 (6)	0.0273 (3)
H12	0.6806	0.3190	0.5602	0.033*
C13	0.6956 (2)	0.1888 (2)	0.48986 (6)	0.0296 (3)
H13	0.8196	0.1703	0.4976	0.036*
C14	0.5992 (2)	0.12433 (19)	0.44025 (6)	0.0274 (3)
C15	0.4157 (2)	0.1594 (2)	0.42935 (6)	0.0290 (3)
H15	0.3478	0.1209	0.3961	0.035*
C16	0.33468 (19)	0.2492 (2)	0.46669 (6)	0.0289 (3)
H16	0.2116	0.2723	0.4585	0.035*
C17	0.8651 (2)	−0.0188 (2)	0.41808 (7)	0.0376 (4)
H17A	0.9414	0.0797	0.4243	0.056*
H17B	0.8996	−0.0853	0.3879	0.056*
H17C	0.8776	−0.0863	0.4518	0.056*
C18	0.5782 (2)	−0.0343 (2)	0.35379 (7)	0.0372 (4)
H18A	0.4968	−0.1195	0.3639	0.056*
H18B	0.6580	−0.0847	0.3307	0.056*
H18C	0.5103	0.0554	0.3333	0.056*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0268 (6)	0.0592 (9)	0.0372 (6)	0.0114 (6)	0.0019 (5)	−0.0009 (6)
N1	0.0266 (6)	0.0241 (6)	0.0277 (6)	0.0029 (5)	0.0078 (5)	0.0028 (5)
N2	0.0270 (6)	0.0255 (6)	0.0289 (6)	0.0028 (5)	0.0059 (5)	0.0028 (5)
N3	0.0321 (7)	0.0366 (8)	0.0309 (7)	0.0068 (6)	0.0054 (5)	−0.0049 (6)
C1	0.0280 (7)	0.0393 (9)	0.0323 (8)	0.0001 (7)	0.0088 (6)	−0.0014 (7)
C2	0.0323 (8)	0.0588 (12)	0.0381 (9)	−0.0076 (8)	0.0042 (7)	−0.0051 (8)
C3	0.0471 (10)	0.0547 (12)	0.0340 (9)	−0.0162 (9)	0.0108 (7)	−0.0096 (8)
C4	0.0501 (10)	0.0347 (9)	0.0360 (8)	−0.0079 (8)	0.0216 (7)	−0.0059 (7)
C5	0.0366 (8)	0.0262 (8)	0.0314 (7)	−0.0008 (6)	0.0158 (6)	0.0018 (6)
C6	0.0384 (9)	0.0340 (9)	0.0397 (9)	0.0090 (7)	0.0206 (7)	0.0047 (7)
C7	0.0294 (8)	0.0444 (10)	0.0398 (9)	0.0115 (7)	0.0140 (7)	0.0091 (7)
C8	0.0268 (7)	0.0332 (8)	0.0326 (8)	0.0067 (6)	0.0083 (6)	0.0064 (6)
C9	0.0255 (7)	0.0232 (7)	0.0293 (7)	0.0022 (6)	0.0092 (5)	0.0043 (6)
C10	0.0292 (7)	0.0242 (7)	0.0293 (7)	−0.0005 (6)	0.0112 (6)	0.0033 (6)
C11	0.0260 (7)	0.0226 (7)	0.0276 (7)	0.0035 (5)	0.0061 (5)	0.0028 (5)
C12	0.0263 (7)	0.0282 (8)	0.0267 (7)	0.0028 (6)	0.0012 (5)	0.0008 (6)
C13	0.0251 (7)	0.0315 (8)	0.0320 (7)	0.0052 (6)	0.0036 (6)	0.0010 (6)
C14	0.0309 (7)	0.0242 (7)	0.0278 (7)	0.0028 (6)	0.0071 (6)	0.0030 (5)
C15	0.0280 (7)	0.0310 (8)	0.0271 (7)	0.0016 (6)	0.0008 (6)	0.0001 (6)
C16	0.0232 (7)	0.0309 (8)	0.0322 (8)	0.0030 (6)	0.0031 (6)	0.0022 (6)
C17	0.0337 (8)	0.0377 (9)	0.0434 (9)	0.0076 (7)	0.0122 (7)	−0.0029 (7)
C18	0.0461 (9)	0.0357 (9)	0.0301 (8)	0.0033 (8)	0.0062 (7)	−0.0054 (7)

Geometric parameters (Å, º)

O1—C8	1.347 (2)	C7—C8	1.423 (2)
O1—H1	1.00 (3)	C7—H7	0.9500
N1—N2	1.2823 (18)	C8—C9	1.409 (2)
N1—C9	1.4095 (18)	C9—C10	1.439 (2)
N2—C11	1.4091 (18)	C11—C16	1.398 (2)
N3—C14	1.3766 (19)	C11—C12	1.405 (2)
N3—C17	1.457 (2)	C12—C13	1.383 (2)
N3—C18	1.458 (2)	C12—H12	0.9500
C1—C2	1.373 (2)	C13—C14	1.421 (2)
C1—C10	1.421 (2)	C13—H13	0.9500
C1—H1A	0.9500	C14—C15	1.416 (2)
C2—C3	1.416 (3)	C15—C16	1.382 (2)
C2—H2	0.9500	C15—H15	0.9500
C3—C4	1.367 (3)	C16—H16	0.9500
C3—H3	0.9500	C17—H17A	0.9800
C4—C5	1.419 (2)	C17—H17B	0.9800
C4—H4	0.9500	C17—H17C	0.9800
C5—C6	1.426 (2)	C18—H18A	0.9800
C5—C10	1.430 (2)	C18—H18B	0.9800
C6—C7	1.361 (3)	C18—H18C	0.9800
C6—H6	0.9500
C8—O1—H1	103.8 (17)	C1—C10—C5	118.33 (14)
N2—N1—C9	114.62 (12)	C1—C10—C9	122.06 (13)
N1—N2—C11	116.84 (12)	C5—C10—C9	119.61 (14)
C14—N3—C17	120.82 (13)	C16—C11—C12	119.11 (13)
C14—N3—C18	120.02 (13)	C16—C11—N2	115.83 (13)
C17—N3—C18	118.39 (13)	C12—C11—N2	125.05 (13)
C2—C1—C10	120.82 (15)	C13—C12—C11	119.89 (14)
C2—C1—H1A	119.6	C13—C12—H12	120.1
C10—C1—H1A	119.6	C11—C12—H12	120.1
C1—C2—C3	120.79 (17)	C12—C13—C14	121.63 (14)
C1—C2—H2	119.6	C12—C13—H13	119.2
C3—C2—H2	119.6	C14—C13—H13	119.2
C4—C3—C2	119.66 (17)	N3—C14—C15	121.22 (14)
C4—C3—H3	120.2	N3—C14—C13	121.32 (14)
C2—C3—H3	120.2	C15—C14—C13	117.45 (14)
C3—C4—C5	121.23 (15)	C16—C15—C14	120.55 (14)
C3—C4—H4	119.4	C16—C15—H15	119.7
C5—C4—H4	119.4	C14—C15—H15	119.7
C4—C5—C6	122.11 (15)	C15—C16—C11	121.30 (14)
C4—C5—C10	119.14 (15)	C15—C16—H16	119.3
C6—C5—C10	118.75 (15)	C11—C16—H16	119.3
C7—C6—C5	121.29 (14)	N3—C17—H17A	109.5
C7—C6—H6	119.4	N3—C17—H17B	109.5
C5—C6—H6	119.4	H17A—C17—H17B	109.5
C6—C7—C8	121.17 (15)	N3—C17—H17C	109.5
C6—C7—H7	119.4	H17A—C17—H17C	109.5
C8—C7—H7	119.4	H17B—C17—H17C	109.5
O1—C8—C9	122.46 (14)	N3—C18—H18A	109.5
O1—C8—C7	117.82 (14)	N3—C18—H18B	109.5
C9—C8—C7	119.72 (15)	H18A—C18—H18B	109.5
C8—C9—N1	124.71 (14)	N3—C18—H18C	109.5
C8—C9—C10	119.44 (13)	H18A—C18—H18C	109.5
N1—C9—C10	115.85 (13)	H18B—C18—H18C	109.5
C9—N1—N2—C11	179.75 (12)	C6—C5—C10—C9	1.3 (2)
C10—C1—C2—C3	−1.2 (3)	C8—C9—C10—C1	179.12 (14)
C1—C2—C3—C4	0.4 (3)	N1—C9—C10—C1	−0.7 (2)
C2—C3—C4—C5	1.0 (3)	C8—C9—C10—C5	−1.7 (2)
C3—C4—C5—C6	178.69 (17)	N1—C9—C10—C5	178.48 (13)
C3—C4—C5—C10	−1.5 (3)	N1—N2—C11—C16	177.19 (13)
C4—C5—C6—C7	−179.95 (16)	N1—N2—C11—C12	−4.0 (2)
C10—C5—C6—C7	0.3 (2)	C16—C11—C12—C13	−1.9 (2)
C5—C6—C7—C8	−1.4 (3)	N2—C11—C12—C13	179.27 (14)
C6—C7—C8—O1	−178.57 (16)	C11—C12—C13—C14	−0.3 (2)
C6—C7—C8—C9	1.0 (3)	C17—N3—C14—C15	−172.56 (15)
O1—C8—C9—N1	−0.1 (2)	C18—N3—C14—C15	−2.8 (2)
C7—C8—C9—N1	−179.59 (15)	C17—N3—C14—C13	8.6 (2)
O1—C8—C9—C10	−179.92 (15)	C18—N3—C14—C13	178.43 (15)
C7—C8—C9—C10	0.6 (2)	C12—C13—C14—N3	−179.03 (15)
N2—N1—C9—C8	1.7 (2)	C12—C13—C14—C15	2.1 (2)
N2—N1—C9—C10	−178.44 (13)	N3—C14—C15—C16	179.44 (15)
C2—C1—C10—C5	0.6 (2)	C13—C14—C15—C16	−1.7 (2)
C2—C1—C10—C9	179.84 (16)	C14—C15—C16—C11	−0.5 (2)
C4—C5—C10—C1	0.7 (2)	C12—C11—C16—C15	2.3 (2)
C6—C5—C10—C1	−179.48 (15)	N2—C11—C16—C15	−178.74 (14)
C4—C5—C10—C9	−178.54 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···N2	1.00 (3)	1.64 (3)	2.5429 (17)	148 (3)

(1b) 1-[4-(diethylamino)phenyldiazenyl]-2-naphthol

Crystal data

C20H21N3O	F(000) = 1360
Mr = 319.40	Dx = 1.260 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 6089 reflections
a = 24.813 (3) Å	θ = 3.6–25.7°
b = 10.7144 (10) Å	µ = 0.08 mm^−1
c = 13.8806 (19) Å	T = 173 K
β = 114.150 (9)°	Rod, black
V = 3367.3 (7) Å^3	0.24 × 0.13 × 0.12 mm
Z = 8

Data collection

Stoe IPDSII two-circle diffractometer	2205 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.048
Graphite monochromator	θmax = 25.6°, θmin = 3.5°
ω scans	h = −30→30
8777 measured reflections	k = −11→13
3140 independent reflections	l = −16→14

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)] = 0.045	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.113	H atoms treated by a mixture of independent and constrained refinement
S = 0.97	w = 1/[σ^2(Fo^2) + (0.0649P)^2] where P = (Fo^2 + 2Fc^2)/3
3140 reflections	(Δ/σ)max < 0.001
221 parameters	Δρmax = 0.12 e Å^−3
0 restraints	Δρmin = −0.19 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	0.59046 (6)	0.42443 (13)	0.81624 (11)	0.0422 (3)
H1O	0.5664 (11)	0.479 (3)	0.755 (2)	0.081 (8)*
N1	0.60552 (5)	0.52327 (12)	0.63180 (10)	0.0256 (3)
N2	0.55964 (5)	0.55367 (12)	0.64777 (11)	0.0262 (3)
N3	0.39342 (5)	0.88487 (12)	0.36783 (11)	0.0270 (3)
C1	0.70163 (7)	0.43599 (17)	0.59303 (15)	0.0352 (4)
H1	0.6742	0.4918	0.5441	0.042*
C2	0.74883 (8)	0.39222 (19)	0.57493 (18)	0.0476 (5)
H2	0.7538	0.4185	0.5137	0.057*
C3	0.78990 (8)	0.3090 (2)	0.6460 (2)	0.0534 (6)
H3	0.8221	0.2793	0.6322	0.064*
C4	0.78341 (7)	0.27104 (18)	0.73458 (19)	0.0483 (6)
H4	0.8115	0.2154	0.7823	0.058*
C5	0.73529 (7)	0.31355 (15)	0.75651 (15)	0.0350 (4)
C6	0.72643 (8)	0.27174 (17)	0.84611 (15)	0.0421 (5)
H6	0.7540	0.2155	0.8941	0.051*
C7	0.67930 (8)	0.31047 (16)	0.86473 (14)	0.0390 (4)
H7	0.6746	0.2815	0.9255	0.047*
C8	0.63725 (7)	0.39342 (16)	0.79446 (13)	0.0311 (4)
C9	0.64416 (6)	0.43945 (14)	0.70563 (13)	0.0261 (3)
C10	0.69364 (6)	0.39808 (15)	0.68467 (14)	0.0290 (4)
C11	0.51996 (6)	0.63610 (14)	0.57426 (13)	0.0244 (3)
C12	0.52580 (6)	0.68268 (14)	0.48452 (13)	0.0262 (4)
H12	0.5583	0.6571	0.4697	0.031*
C13	0.48492 (7)	0.76516 (15)	0.41759 (13)	0.0277 (4)
H13	0.4902	0.7965	0.3580	0.033*
C14	0.43488 (6)	0.80471 (14)	0.43549 (12)	0.0235 (3)
C15	0.42941 (6)	0.75475 (15)	0.52571 (13)	0.0260 (4)
H15	0.3968	0.7785	0.5407	0.031*
C16	0.47055 (6)	0.67245 (14)	0.59190 (12)	0.0259 (4)
H16	0.4653	0.6395	0.6510	0.031*
C17	0.40040 (7)	0.94022 (16)	0.27703 (13)	0.0305 (4)
H17A	0.3610	0.9646	0.2237	0.037*
H17B	0.4166	0.8762	0.2447	0.037*
C18	0.44072 (8)	1.05429 (18)	0.30459 (16)	0.0423 (5)
H18A	0.4437	1.0858	0.2406	0.063*
H18B	0.4801	1.0309	0.3565	0.063*
H18C	0.4243	1.1194	0.3343	0.063*
C19	0.34556 (6)	0.93391 (15)	0.39363 (13)	0.0292 (4)
H19A	0.3281	0.8639	0.4176	0.035*
H19B	0.3143	0.9684	0.3286	0.035*
C20	0.36477 (7)	1.03509 (16)	0.47845 (15)	0.0362 (4)
H20A	0.3307	1.0623	0.4916	0.054*
H20B	0.3808	1.1063	0.4545	0.054*
H20C	0.3952	1.0016	0.5438	0.054*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0520 (7)	0.0472 (8)	0.0341 (7)	0.0103 (6)	0.0245 (6)	0.0078 (7)
N1	0.0262 (6)	0.0219 (7)	0.0262 (7)	−0.0013 (5)	0.0080 (5)	−0.0023 (6)
N2	0.0274 (6)	0.0231 (7)	0.0274 (7)	0.0004 (5)	0.0106 (6)	−0.0016 (6)
N3	0.0256 (6)	0.0265 (7)	0.0270 (7)	0.0019 (5)	0.0089 (5)	0.0028 (6)
C1	0.0318 (8)	0.0325 (9)	0.0432 (11)	−0.0068 (7)	0.0172 (8)	−0.0072 (8)
C2	0.0377 (9)	0.0476 (12)	0.0649 (14)	−0.0142 (9)	0.0284 (10)	−0.0184 (10)
C3	0.0283 (9)	0.0490 (12)	0.0846 (18)	−0.0049 (8)	0.0246 (10)	−0.0276 (12)
C4	0.0259 (8)	0.0351 (11)	0.0696 (15)	0.0011 (7)	0.0048 (9)	−0.0175 (11)
C5	0.0257 (8)	0.0248 (9)	0.0421 (11)	−0.0008 (7)	0.0012 (7)	−0.0097 (8)
C6	0.0396 (9)	0.0276 (9)	0.0375 (11)	0.0024 (7)	−0.0062 (8)	−0.0009 (8)
C7	0.0487 (10)	0.0325 (10)	0.0250 (9)	−0.0001 (8)	0.0042 (8)	0.0022 (8)
C8	0.0370 (8)	0.0270 (9)	0.0248 (9)	−0.0013 (7)	0.0082 (7)	−0.0036 (7)
C9	0.0267 (7)	0.0204 (8)	0.0254 (8)	−0.0008 (6)	0.0048 (6)	−0.0026 (7)
C10	0.0249 (7)	0.0220 (8)	0.0345 (10)	−0.0046 (6)	0.0065 (7)	−0.0073 (7)
C11	0.0251 (7)	0.0196 (8)	0.0256 (8)	−0.0015 (6)	0.0074 (6)	−0.0010 (7)
C12	0.0264 (7)	0.0254 (8)	0.0290 (9)	0.0010 (6)	0.0135 (7)	−0.0018 (7)
C13	0.0317 (8)	0.0298 (9)	0.0243 (9)	0.0001 (6)	0.0142 (7)	0.0014 (7)
C14	0.0230 (7)	0.0202 (8)	0.0240 (8)	−0.0030 (6)	0.0062 (6)	−0.0029 (7)
C15	0.0231 (7)	0.0264 (8)	0.0302 (9)	−0.0010 (6)	0.0127 (7)	−0.0009 (7)
C16	0.0294 (7)	0.0259 (8)	0.0244 (8)	−0.0039 (6)	0.0129 (7)	0.0002 (7)
C17	0.0312 (8)	0.0308 (9)	0.0246 (9)	0.0018 (7)	0.0065 (7)	0.0041 (7)
C18	0.0450 (9)	0.0422 (11)	0.0410 (11)	−0.0108 (8)	0.0190 (8)	0.0015 (9)
C19	0.0224 (7)	0.0286 (9)	0.0333 (9)	0.0021 (6)	0.0080 (7)	0.0009 (7)
C20	0.0363 (8)	0.0306 (9)	0.0423 (11)	−0.0004 (7)	0.0167 (8)	−0.0055 (8)

Geometric parameters (Å, º)

O1—C8	1.355 (2)	C9—C10	1.442 (2)
O1—H1O	1.00 (3)	C11—C16	1.400 (2)
N1—N2	1.2876 (16)	C11—C12	1.403 (2)
N1—C9	1.404 (2)	C12—C13	1.379 (2)
N2—C11	1.403 (2)	C12—H12	0.9500
N3—C14	1.374 (2)	C13—C14	1.427 (2)
N3—C17	1.466 (2)	C13—H13	0.9500
N3—C19	1.4706 (19)	C14—C15	1.419 (2)
C1—C2	1.377 (2)	C15—C16	1.377 (2)
C1—C10	1.424 (2)	C15—H15	0.9500
C1—H1	0.9500	C16—H16	0.9500
C2—C3	1.408 (3)	C17—C18	1.526 (2)
C2—H2	0.9500	C17—H17A	0.9900
C3—C4	1.366 (3)	C17—H17B	0.9900
C3—H3	0.9500	C18—H18A	0.9800
C4—C5	1.422 (3)	C18—H18B	0.9800
C4—H4	0.9500	C18—H18C	0.9800
C5—C6	1.421 (3)	C19—C20	1.526 (2)
C5—C10	1.428 (2)	C19—H19A	0.9900
C6—C7	1.362 (3)	C19—H19B	0.9900
C6—H6	0.9500	C20—H20A	0.9800
C7—C8	1.413 (2)	C20—H20B	0.9800
C7—H7	0.9500	C20—H20C	0.9800
C8—C9	1.402 (2)
C8—O1—H1O	103.0 (14)	C13—C12—C11	120.74 (14)
N2—N1—C9	115.08 (13)	C13—C12—H12	119.6
N1—N2—C11	116.16 (13)	C11—C12—H12	119.6
C14—N3—C17	121.45 (12)	C12—C13—C14	121.71 (15)
C14—N3—C19	120.69 (13)	C12—C13—H13	119.1
C17—N3—C19	117.13 (13)	C14—C13—H13	119.1
C2—C1—C10	120.36 (18)	N3—C14—C15	121.60 (13)
C2—C1—H1	119.8	N3—C14—C13	121.89 (14)
C10—C1—H1	119.8	C15—C14—C13	116.50 (14)
C1—C2—C3	120.9 (2)	C16—C15—C14	121.20 (14)
C1—C2—H2	119.5	C16—C15—H15	119.4
C3—C2—H2	119.5	C14—C15—H15	119.4
C4—C3—C2	120.04 (17)	C15—C16—C11	121.64 (14)
C4—C3—H3	120.0	C15—C16—H16	119.2
C2—C3—H3	120.0	C11—C16—H16	119.2
C3—C4—C5	121.04 (19)	N3—C17—C18	113.86 (14)
C3—C4—H4	119.5	N3—C17—H17A	108.8
C5—C4—H4	119.5	C18—C17—H17A	108.8
C6—C5—C4	122.02 (17)	N3—C17—H17B	108.8
C6—C5—C10	118.95 (15)	C18—C17—H17B	108.8
C4—C5—C10	119.00 (19)	H17A—C17—H17B	107.7
C7—C6—C5	121.50 (16)	C17—C18—H18A	109.5
C7—C6—H6	119.2	C17—C18—H18B	109.5
C5—C6—H6	119.2	H18A—C18—H18B	109.5
C6—C7—C8	120.63 (17)	C17—C18—H18C	109.5
C6—C7—H7	119.7	H18A—C18—H18C	109.5
C8—C7—H7	119.7	H18B—C18—H18C	109.5
O1—C8—C9	122.28 (15)	N3—C19—C20	114.40 (12)
O1—C8—C7	117.26 (16)	N3—C19—H19A	108.7
C9—C8—C7	120.46 (15)	C20—C19—H19A	108.7
C8—C9—N1	125.04 (14)	N3—C19—H19B	108.7
C8—C9—C10	119.31 (14)	C20—C19—H19B	108.7
N1—C9—C10	115.64 (14)	H19A—C19—H19B	107.6
C1—C10—C5	118.62 (15)	C19—C20—H20A	109.5
C1—C10—C9	122.24 (15)	C19—C20—H20B	109.5
C5—C10—C9	119.12 (16)	H20A—C20—H20B	109.5
C16—C11—N2	116.88 (14)	C19—C20—H20C	109.5
C16—C11—C12	118.17 (14)	H20A—C20—H20C	109.5
N2—C11—C12	124.94 (13)	H20B—C20—H20C	109.5
C9—N1—N2—C11	−179.21 (12)	N1—C9—C10—C1	−2.3 (2)
C10—C1—C2—C3	0.3 (3)	C8—C9—C10—C5	−1.6 (2)
C1—C2—C3—C4	−0.3 (3)	N1—C9—C10—C5	179.47 (13)
C2—C3—C4—C5	0.4 (3)	N1—N2—C11—C16	−178.51 (13)
C3—C4—C5—C6	177.63 (18)	N1—N2—C11—C12	2.5 (2)
C3—C4—C5—C10	−0.5 (3)	C16—C11—C12—C13	2.1 (2)
C4—C5—C6—C7	−178.18 (17)	N2—C11—C12—C13	−178.92 (14)
C10—C5—C6—C7	0.0 (3)	C11—C12—C13—C14	−1.1 (2)
C5—C6—C7—C8	0.4 (3)	C17—N3—C14—C15	177.54 (14)
C6—C7—C8—O1	177.78 (16)	C19—N3—C14—C15	7.6 (2)
C6—C7—C8—C9	−1.5 (3)	C17—N3—C14—C13	−3.9 (2)
O1—C8—C9—N1	1.7 (3)	C19—N3—C14—C13	−173.86 (14)
C7—C8—C9—N1	−179.13 (14)	C12—C13—C14—N3	−178.64 (14)
O1—C8—C9—C10	−177.19 (14)	C12—C13—C14—C15	0.0 (2)
C7—C8—C9—C10	2.0 (2)	N3—C14—C15—C16	178.64 (14)
N2—N1—C9—C8	−2.9 (2)	C13—C14—C15—C16	0.0 (2)
N2—N1—C9—C10	175.97 (13)	C14—C15—C16—C11	1.1 (2)
C2—C1—C10—C5	−0.4 (2)	N2—C11—C16—C15	178.82 (14)
C2—C1—C10—C9	−178.64 (16)	C12—C11—C16—C15	−2.1 (2)
C6—C5—C10—C1	−177.73 (15)	C14—N3—C17—C18	−81.70 (19)
C4—C5—C10—C1	0.5 (2)	C19—N3—C17—C18	88.61 (17)
C6—C5—C10—C9	0.6 (2)	C14—N3—C19—C20	74.87 (19)
C4—C5—C10—C9	178.80 (15)	C17—N3—C19—C20	−95.52 (17)
C8—C9—C10—C1	176.66 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···N2	1.00 (3)	1.64 (3)	2.5510 (19)	149 (2)