An azo dye mol­ecule having a pyridine-2,6-dione backbone

The title azo dye, 2-(2-methoxy­ethoxy)ethyl 4-[(5-cyano-1-ethyl-4-methyl-2,6-dioxo-1,2,3,6-tetra­hydro­pyridin-3-ylidene)hydrazino]benzoate, C₂₁H₂₄N₄O₆, with a 1-ethyl-5-cyano-2-hydr­oxy-4-methyl-6-pyridone component, crystallizes in the hydrazone form. Hydrogen bonding mediates the formation of four-mol­ecule aggregates, which are further grouped into an extended structure by π–π stacking inter­actions between the aromatic rings of adjacent mol­ecules, with a centroid–centroid separation of 3.697 (2) Å.

S1. Comment

Azo dyes have found widespread application in the textile and food industries and elsewhere. Those having 1-alkyl-5-cyano-2-hydroxy-4-methyl-6-pyridone components have good coloration properties and give bright greenish-yellow hues. More importantly, they have excellent colour fastness to washing. This type of molecule has two enantiotropic isomers, i.e. the 2-hydroxy-6-pyridone form and the pyridine-2,6-dione form. To date, there is only one structural report on these two types of backbones (Black et al., 1992). In this communication, we report the single-crystal structure of a yellow azo dye, (I), using 1-ethyl-5-cyano-2-hydroxy-4-methyl-6-pyridone as the coupling component.

The molecular structure of (I) with the atom-numbering scheme is shown in Fig. 1, while selected bond distances and angles are given in Table 1. The bond distances and angles of the phenyl ring, the pyridine-2,6-dione ring and the 2-(2-methoxyethoxy)ethyl ester moiety in this structure are in the normal ranges (Reference for standard values?).

The dye exists in the hydrazone form, which can be deduced by the relevant bond lengths [C1—O2 = 1.234 (2), C2—N2 = 1.320 (2), C1—C2 = 1.471 (3), C2—C3 = 1.441 (2) and N1—N2 = 1.307 (2) Å]; the first two exhibit partial double-bond character, while the other three display predominantly single-bond character. Furthermore, higher R₁ and wR₂ values are obtained if an H atom is added to atom O2 to model a hydroxyl group. The whole molecule, except for the ethyl and 2-methoxyethoxyethyl ester groups, is essentially planar. The dihedral angle between the two aromatic rings is 0.7 (2)°. The ethyl and 2-methoxyethoxyethyl ester groups of this molecule adopt cis configurations with respect to the molecular plane.

In the crystal packing of (I), π–π stacking and hydrogen-bonding interactions are observed between neighbouring molecules. As illustrated in Fig. 2, every four contiguous molecules can be classified as one group, with a centroid–centroid separation of 3.697 (2) Å between the aromatic rings. Weak C—H···O hydrogen bonds also connect the packed molecules (Table 2). The ethyl and 2-methoxyethoxyethyl ester groups of these four molecules point to the outside of each aggregate, minimizing the internal steric hindrance and, at the same time, deterring adjacent groups from further stacking. Instead, all the groups of molecules are parallel to one another with van der Waals interactions between adjacent pairs (Fig. 3). This separation is larger than that found in a similar structure in which n-butyl and Cl groups replace the ethyl and 2-methoxyethoxyethyl ester groups, respectively (Black et al., 1992), where an interlayer contact of 3.3 Å was observed among all the phenyl rings due to the less pronounced spatial crowding. In addition, a strong intramolecular N—H···O hydrogen bond (Table 2) is present between atoms N1 and O2, forming a six-membered ring.

Electrospray ionization mass spectrometry (ESI-MS), a soft ionization technique, is a powerful tool to analyze the structures of azo dyes (Lemr et al., 2000). Both positive-ion ESI-MS and negative-ion ESI-MS have been carried out, giving peaks corresponding to the molecular ions as well as the dimeric sodium(I) salts in different abundances for different ESI-MS.

S2. Experimental

Compound (I) was prepared as a yellow powder via the method described by Horakova & Lycka (1988), by coupling of diazotized 2-(2-methoxyethoxy)ethyl-4-aminobenzoate with 1-ethyl-5-cyano-2-hydroxy-4-methyl-6-pyridone. Spectroscopic analysis: ¹H NMR (500 MHz, CDCl₃, 298 K, TMS, p.p.m.): 14.98 (s, 1H), 8.18 (d, J = 8.5 Hz, 2H), 7.54 (d, J = 9.0 Hz, 2H), 4.53 (t, 2H), 4.07 (t, 2H), 3.88 (t, 2H), 3.73 (t, 2H), 3.60 (t, 2H), 2.65 (s, 3H), 1.62 (s, 3H), 1.28 (t, 3H); ¹³C NMR (125 MHz, CDCl₃, 298 K, TMS, p.p.m.): 165.55, 161.45, 159.56, 158.40, 144.24, 131.73, 128.38, 124.15, 116.51, 114.09, 103.33, 71.96, 70.61, 69.26, 64.38, 59.12, 35.32, 16.63, 12.97. Elemental analysis, calculated for C₂₁H₂₄N₄O₆: C 58.87, H 5.65, N 13.08%; found: C 58.89, H 5.62, N 13.16%. ESI-MS (FAB, m/z): positive-ion, 429.3 (50%) [M]⁺, 879.1 (100%) [M₂Na]⁺; negative-ion, 427.6 (100%) [M - H]⁻, 877.5 (74%) [M₂Na − 2H]⁻. Orange single crystals of (I) suitable for X-ray analysis were grown from a mixture of methanol and acetone in a ratio of 2:1 (v/v) by slow evaporation at room temperature in air.

S3. Refinement

H atoms were placed in geometrically idealized positions, with C—H = 0.95—0.99 Å and N—H = 0.88 Å, and refined as riding atoms, with U_iso(H) = 1.5_eq(N and methyl C) or 1.2_eq(C) for the other C atoms.

Computing details

Data collection: CrystalClear (Molecular Structure Corporation & Rigaku, 2001); cell refinement: CrystalClear; data reduction: TEXSAN (Molecular Structure Corporation & Rigaku, 2000); program(s) used to solve structure: SHELXTL (Bruker, 2000); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A drawing of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. The intramolecular N—H···O hydrogen bond is shown as a dashed line.
	Fig. 2. A perspective view of four adjacent molecules of (I) joined by hydrogen bonds and π–π stacking interactions between the aromatic rings. For clarity, labels are given only once for the hydrogen-bond contacts. Hydrogen bonds and and centroid–centroid π–π stacking separation are shown as dashed lines. [Symmetry codes: (i) 1 − x, 1 − y, −z; (ii) x, −1 + y, z.]
	Fig. 3. A packing diagram for (I), viewed along the common plane of the phenyl rings.

2-(2-Methoxyethoxy)ethyl 4-[5-cyano-1-ethyl-4-methyl-2,6-dioxo-1,2,3,6-tetrahydropyridin-3- yl)diazenyl]benzoate

Crystal data

C21H24N4O6	F(000) = 904
Mr = 428.44	Dx = 1.351 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 8347 reflections
a = 8.7074 (17) Å	θ = 3.2–27.5°
b = 17.749 (4) Å	µ = 0.10 mm^−1
c = 14.081 (3) Å	T = 120 K
β = 104.53 (3)°	Block, orange
V = 2106.6 (8) Å^3	0.20 × 0.20 × 0.10 mm
Z = 4

Data collection

Rigaku Mercury CCD area-detector diffractometer	3648 independent reflections
Radiation source: Rigaku rotating anode	3434 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.098
Detector resolution: 14.6199 pixels mm^-1	θmax = 25.0°, θmin = 3.2°
ϕ and ω scans	h = −10→10
Absorption correction: multi-scan (REQAB, Jacobson, 1998)	k = −21→19
Tmin = 0.978, Tmax = 0.988	l = −16→16
17551 measured reflections

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)] = 0.054	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.142	H-atom parameters constrained
S = 1.16	w = 1/[σ^2(Fo^2) + (0.0632P)^2 + 0.9136P] where P = (Fo^2 + 2Fc^2)/3
3648 reflections	(Δ/σ)max < 0.001
283 parameters	Δρmax = 0.34 e Å^−3
0 restraints	Δρmin = −0.21 e Å^−3

Special details

Experimental. The structure was solved by direct methods (Bruker, 2000) and successive difference Fourier syntheses.

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
C1	0.2587 (2)	0.66691 (9)	0.03834 (12)	0.0216 (4)
C2	0.4236 (2)	0.64715 (9)	0.08728 (12)	0.0205 (4)
C3	0.5409 (2)	0.70511 (10)	0.11978 (12)	0.0209 (4)
C4	0.4949 (2)	0.77807 (9)	0.10227 (12)	0.0222 (4)
C5	0.3341 (2)	0.80011 (10)	0.04999 (13)	0.0232 (4)
C6	0.7058 (2)	0.68335 (10)	0.17336 (14)	0.0259 (4)
H6A	0.7705	0.7288	0.1910	0.039*
H6B	0.7522	0.6513	0.1311	0.039*
H6C	0.7028	0.6556	0.2331	0.039*
C7	0.6032 (2)	0.83983 (10)	0.13354 (13)	0.0263 (4)
C8	0.0611 (2)	0.76509 (11)	−0.02926 (16)	0.0339 (5)
H8A	0.0046	0.7222	−0.0675	0.041*
H8B	0.0641	0.8068	−0.0755	0.041*
C9	−0.0276 (3)	0.79023 (14)	0.0440 (2)	0.0503 (6)
H9A	−0.0380	0.7478	0.0866	0.075*
H9B	−0.1333	0.8080	0.0093	0.075*
H9C	0.0307	0.8312	0.0840	0.075*
C10	0.4334 (2)	0.44700 (9)	0.10907 (12)	0.0199 (4)
C11	0.3275 (2)	0.38739 (10)	0.08318 (13)	0.0226 (4)
H11	0.2195	0.3965	0.0509	0.027*
C12	0.3817 (2)	0.31436 (10)	0.10522 (13)	0.0223 (4)
H12	0.3102	0.2733	0.0875	0.027*
C13	0.5396 (2)	0.30042 (9)	0.15294 (12)	0.0211 (4)
C14	0.6425 (2)	0.36130 (10)	0.18007 (13)	0.0233 (4)
H14	0.7498	0.3524	0.2140	0.028*
C15	0.5910 (2)	0.43437 (9)	0.15842 (13)	0.0223 (4)
H15	0.6621	0.4755	0.1770	0.027*
C16	0.6019 (2)	0.22251 (10)	0.17546 (12)	0.0219 (4)
C17	0.5421 (2)	0.09245 (9)	0.14635 (14)	0.0237 (4)
H17A	0.5782	0.0819	0.2175	0.028*
H17B	0.6296	0.0804	0.1156	0.028*
C18	0.3985 (2)	0.04638 (9)	0.10103 (13)	0.0244 (4)
H18A	0.3580	0.0600	0.0310	0.029*
H18B	0.4261	−0.0078	0.1051	0.029*
C19	0.1357 (2)	0.02395 (11)	0.10921 (14)	0.0311 (5)
H19A	0.1544	−0.0309	0.1057	0.037*
H19B	0.0932	0.0428	0.0416	0.037*
C20	0.0182 (2)	0.03812 (11)	0.16852 (14)	0.0289 (4)
H20A	0.0094	0.0929	0.1790	0.035*
H20B	−0.0875	0.0192	0.1328	0.035*
C21	−0.0363 (3)	0.01511 (15)	0.32020 (17)	0.0450 (6)
H21A	−0.0435	0.0695	0.3304	0.067*
H21B	0.0043	−0.0098	0.3836	0.067*
H21C	−0.1418	−0.0047	0.2887	0.067*
N1	0.37656 (18)	0.52020 (8)	0.08410 (11)	0.0217 (3)
H1A	0.2766	0.5276	0.0532	0.033*
N2	0.47350 (18)	0.57733 (8)	0.10714 (10)	0.0205 (3)
N3	0.22446 (18)	0.74223 (8)	0.01975 (11)	0.0241 (4)
N4	0.6884 (2)	0.88943 (9)	0.15767 (13)	0.0368 (4)
O1	0.29535 (17)	0.86578 (7)	0.03266 (10)	0.0303 (3)
O2	0.15424 (15)	0.61870 (7)	0.01372 (10)	0.0279 (3)
O3	0.73078 (16)	0.20713 (7)	0.22760 (11)	0.0337 (4)
O4	0.49677 (15)	0.17102 (6)	0.13001 (9)	0.0234 (3)
O5	0.28051 (15)	0.06090 (7)	0.15273 (9)	0.0238 (3)
O6	0.06740 (16)	0.00129 (9)	0.25957 (11)	0.0365 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0273 (10)	0.0195 (8)	0.0197 (9)	−0.0015 (7)	0.0088 (7)	−0.0016 (7)
C2	0.0275 (9)	0.0188 (8)	0.0172 (8)	−0.0020 (7)	0.0096 (7)	−0.0008 (7)
C3	0.0269 (10)	0.0214 (9)	0.0162 (8)	−0.0028 (7)	0.0091 (7)	0.0000 (7)
C4	0.0303 (10)	0.0188 (8)	0.0198 (8)	−0.0036 (7)	0.0105 (7)	−0.0008 (7)
C5	0.0315 (10)	0.0193 (9)	0.0221 (9)	0.0003 (7)	0.0127 (8)	−0.0002 (7)
C6	0.0268 (10)	0.0236 (9)	0.0265 (9)	−0.0036 (7)	0.0050 (8)	0.0031 (7)
C7	0.0351 (11)	0.0219 (9)	0.0237 (9)	0.0009 (8)	0.0107 (8)	0.0020 (7)
C8	0.0277 (11)	0.0272 (10)	0.0422 (12)	0.0021 (8)	0.0001 (9)	0.0016 (9)
C9	0.0298 (12)	0.0456 (13)	0.0777 (18)	−0.0027 (10)	0.0175 (12)	−0.0100 (12)
C10	0.0254 (9)	0.0174 (8)	0.0190 (8)	−0.0016 (7)	0.0094 (7)	−0.0021 (6)
C11	0.0221 (9)	0.0214 (9)	0.0248 (9)	−0.0010 (7)	0.0070 (7)	−0.0023 (7)
C12	0.0244 (9)	0.0189 (8)	0.0246 (9)	−0.0049 (7)	0.0082 (7)	−0.0020 (7)
C13	0.0275 (9)	0.0198 (9)	0.0186 (8)	−0.0026 (7)	0.0105 (7)	−0.0016 (7)
C14	0.0229 (9)	0.0240 (9)	0.0222 (9)	−0.0021 (7)	0.0044 (7)	−0.0004 (7)
C15	0.0250 (9)	0.0183 (8)	0.0236 (9)	−0.0069 (7)	0.0060 (7)	−0.0031 (7)
C16	0.0246 (10)	0.0227 (9)	0.0210 (9)	−0.0028 (7)	0.0106 (8)	0.0008 (7)
C17	0.0283 (10)	0.0162 (8)	0.0294 (9)	0.0034 (7)	0.0121 (8)	0.0033 (7)
C18	0.0336 (10)	0.0169 (8)	0.0258 (9)	0.0021 (7)	0.0133 (8)	−0.0010 (7)
C19	0.0326 (11)	0.0321 (10)	0.0275 (10)	−0.0090 (8)	0.0054 (8)	−0.0071 (8)
C20	0.0235 (9)	0.0307 (10)	0.0290 (10)	0.0018 (8)	0.0000 (8)	0.0034 (8)
C21	0.0286 (11)	0.0701 (16)	0.0379 (12)	0.0005 (11)	0.0116 (10)	0.0070 (11)
N1	0.0240 (8)	0.0177 (7)	0.0232 (8)	−0.0027 (6)	0.0058 (6)	−0.0017 (6)
N2	0.0279 (8)	0.0177 (7)	0.0173 (7)	−0.0025 (6)	0.0082 (6)	−0.0004 (6)
N3	0.0265 (8)	0.0204 (7)	0.0261 (8)	0.0008 (6)	0.0078 (6)	0.0009 (6)
N4	0.0455 (11)	0.0241 (8)	0.0397 (10)	−0.0096 (8)	0.0086 (8)	−0.0007 (7)
O1	0.0374 (8)	0.0185 (6)	0.0380 (8)	0.0040 (5)	0.0150 (6)	0.0018 (5)
O2	0.0260 (7)	0.0230 (6)	0.0336 (7)	−0.0027 (5)	0.0053 (6)	−0.0008 (5)
O3	0.0272 (8)	0.0268 (7)	0.0419 (8)	0.0013 (6)	−0.0011 (6)	0.0041 (6)
O4	0.0261 (7)	0.0151 (6)	0.0290 (7)	0.0005 (5)	0.0069 (5)	0.0014 (5)
O5	0.0254 (7)	0.0229 (6)	0.0236 (6)	−0.0037 (5)	0.0073 (5)	−0.0054 (5)
O6	0.0219 (7)	0.0515 (9)	0.0371 (8)	0.0078 (6)	0.0092 (6)	0.0157 (7)

Geometric parameters (Å, º)

C1—O2	1.234 (2)	C12—H12	0.9500
C1—N3	1.380 (2)	C13—C14	1.395 (2)
C1—C2	1.471 (3)	C13—C16	1.490 (2)
C2—N2	1.320 (2)	C14—C15	1.381 (2)
C2—C3	1.441 (2)	C14—H14	0.9500
C3—C4	1.360 (2)	C15—H15	0.9500
C3—C6	1.495 (3)	C16—O3	1.208 (2)
C4—C7	1.441 (3)	C16—O4	1.337 (2)
C4—C5	1.462 (3)	C17—O4	1.452 (2)
C5—O1	1.221 (2)	C17—C18	1.496 (3)
C5—N3	1.395 (2)	C17—H17A	0.9900
C6—H6A	0.9800	C17—H17B	0.9900
C6—H6B	0.9800	C18—O5	1.424 (2)
C6—H6C	0.9800	C18—H18A	0.9900
C7—N4	1.147 (3)	C18—H18B	0.9900
C8—N3	1.474 (2)	C19—O5	1.417 (2)
C8—C9	1.504 (3)	C19—C20	1.496 (3)
C8—H8A	0.9900	C19—H19A	0.9900
C8—H8B	0.9900	C19—H19B	0.9900
C9—H9A	0.9800	C20—O6	1.407 (2)
C9—H9B	0.9800	C20—H20A	0.9900
C9—H9C	0.9800	C20—H20B	0.9900
C10—C11	1.391 (2)	C21—O6	1.411 (3)
C10—C15	1.392 (3)	C21—H21A	0.9800
C10—N1	1.403 (2)	C21—H21B	0.9800
C11—C12	1.388 (2)	C21—H21C	0.9800
C11—H11	0.9500	N1—N2	1.307 (2)
C12—C13	1.392 (3)	N1—H1A	0.8800
O2—C1—N3	120.63 (17)	C13—C14—H14	119.5
O2—C1—C2	122.05 (16)	C14—C15—C10	119.10 (16)
N3—C1—C2	117.32 (15)	C14—C15—H15	120.5
N2—C2—C3	115.69 (16)	C10—C15—H15	120.5
N2—C2—C1	123.65 (15)	O3—C16—O4	123.80 (16)
C3—C2—C1	120.63 (15)	O3—C16—C13	124.88 (16)
C4—C3—C2	117.98 (17)	O4—C16—C13	111.31 (15)
C4—C3—C6	122.64 (16)	O4—C17—C18	107.01 (14)
C2—C3—C6	119.36 (15)	O4—C17—H17A	110.3
C3—C4—C7	121.92 (17)	C18—C17—H17A	110.3
C3—C4—C5	123.19 (16)	O4—C17—H17B	110.3
C7—C4—C5	114.89 (15)	C18—C17—H17B	110.3
O1—C5—N3	120.55 (17)	H17A—C17—H17B	108.6
O1—C5—C4	122.54 (17)	O5—C18—C17	108.41 (14)
N3—C5—C4	116.91 (15)	O5—C18—H18A	110.0
C3—C6—H6A	109.5	C17—C18—H18A	110.0
C3—C6—H6B	109.5	O5—C18—H18B	110.0
H6A—C6—H6B	109.5	C17—C18—H18B	110.0
C3—C6—H6C	109.5	H18A—C18—H18B	108.4
H6A—C6—H6C	109.5	O5—C19—C20	109.87 (15)
H6B—C6—H6C	109.5	O5—C19—H19A	109.7
N4—C7—C4	179.3 (2)	C20—C19—H19A	109.7
N3—C8—C9	111.23 (18)	O5—C19—H19B	109.7
N3—C8—H8A	109.4	C20—C19—H19B	109.7
C9—C8—H8A	109.4	H19A—C19—H19B	108.2
N3—C8—H8B	109.4	O6—C20—C19	109.62 (15)
C9—C8—H8B	109.4	O6—C20—H20A	109.7
H8A—C8—H8B	108.0	C19—C20—H20A	109.7
C8—C9—H9A	109.5	O6—C20—H20B	109.7
C8—C9—H9B	109.5	C19—C20—H20B	109.7
H9A—C9—H9B	109.5	H20A—C20—H20B	108.2
C8—C9—H9C	109.5	O6—C21—H21A	109.5
H9A—C9—H9C	109.5	O6—C21—H21B	109.5
H9B—C9—H9C	109.5	H21A—C21—H21B	109.5
C11—C10—C15	120.94 (16)	O6—C21—H21C	109.5
C11—C10—N1	118.03 (16)	H21A—C21—H21C	109.5
C15—C10—N1	121.03 (15)	H21B—C21—H21C	109.5
C12—C11—C10	119.06 (17)	N2—N1—C10	119.41 (15)
C12—C11—H11	120.5	N2—N1—H1A	120.3
C10—C11—H11	120.5	C10—N1—H1A	120.3
C11—C12—C13	120.90 (16)	N1—N2—C2	121.20 (15)
C11—C12—H12	119.6	C1—N3—C5	123.83 (16)
C13—C12—H12	119.6	C1—N3—C8	119.52 (15)
C12—C13—C14	118.89 (16)	C5—N3—C8	116.53 (15)
C12—C13—C16	122.01 (16)	C16—O4—C17	117.02 (14)
C14—C13—C16	119.10 (16)	C19—O5—C18	111.90 (13)
C15—C14—C13	121.09 (17)	C20—O6—C21	112.06 (16)
C15—C14—H14	119.5

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O2	0.88	1.94	2.612 (2)	132
C6—H6C···O5^i	0.98	2.31	3.254 (2)	163
C15—H15···O6^i	0.95	2.35	3.141 (2)	141
C17—H17B···O1^ii	0.99	2.53	3.271 (2)	132
C19—H19A···O1^iii	0.99	2.56	3.424 (2)	146

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