Crystal structure of (E)-2,6-dimeth-oxy-4-{[(4-meth-oxy-phen-yl)imino]-meth-yl}phenol.

In the title compound, C16H17NO4, the dihedral angle between benzene rings is 72.7 (2)°. The meth-oxy groups are rotated by 2.4 (2) and -4.9 (2) (benzil-idene moiety) and by 5.6 (3)° (aniline moiety) relative to the adjacent benzene ring. In the crystal, the mol-ecules are linked into chains along [101] through C-H⋯O and O-H⋯N hydrogen bonds.

Chemical context

Syringaldehyde is a product of the catalytic decomposition of lignin (Crestini et al., 2010 ▸). Syringaldehyde is widely used as a mol­ecular marker to monitor pollution sources and detect the extent of combustion (Robinson et al., 2006 ▸). It is also known to be an anti­oxidant (Ibrahim et al., 2012 ▸), anti­cancer, anti-inflammatory (Duke, 2003 ▸) and anti­fungal agent (Gurpilhares et al., 2006 ▸). In addition, its Schiff bases are known to exhibit a wide range of biological activities (Shi & Zhou, 2011 ▸; da Silva et al., 2011 ▸).

Structural commentary

The mol­ecular structure of the title molecule is shown on Fig. 1 ▸. The compound has a trans-configuration of the C9=N1 double bond. The mol­ecule has a non-planar conformation with the two benzene rings forming a dihedral angle of 72.7 (2)°. The meth­oxy groups are almost co-planar with the planes of the adjacent aromatic rings [the C1—O1—C4—C3, C2—O3—C6—C7 and C16—O4—C13—C12 torsion angles are −4.9 (2), 2.4 (2) and 5.6 (3)°, respectively].

Figure 1

A view of the mol­ecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 40% probability level.

Supra­molecular features

In the crystal, the mol­ecules are connected via C7—H7⋯O2ii and O2—H2⋯N1i hydrogen bonding (Table 1 ▸), forming chains along the [101] direction (Fig. 2 ▸).

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H2⋯N1i	0.82	2.21	2.9415 (18)	149
C7—H7⋯O2ii	0.93	2.29	3.2043 (18)	167

Symmetry codes: (i) ; (ii) .

Figure 2

A view along the a axis of the crystal packing. Dashed lines indicate hydrogen bonds (see Table 1 ▸).

Database survey

A search of the Cambridge Structural Database (CSD version 5.39, update of May 2018; Groom et al., 2016 ▸) revealed the structures of five similar Schiff bases based on p-meth­oxy­aniline and p-hy­droxy­benzaldehyde: 4-[(4-meth­oxy­phenyl­imino)­meth­yl]phenol, (I) (VUKDEK; Yeap et al., 1992 ▸), (E)-5-meth­oxy-2-[(4-meth­oxy­phenyl­imino)­meth­yl]phenol, (II) (NURNAQ; Sahin et al., 2010 ▸), 2-meth­oxy-4-{[(4-meth­oxy­phen­yl)imino]­meth­yl}phenol, (III) (MOTLIR; Singh et al., 2008 ▸), 2,6-di-tert-butyl-4-[(4-meth­oxy­phenyl­imino)­meth­yl]phenol, (IV) (WEFTEH; Xin et al., 2006 ▸) and 5-bromo-2-meth­oxy-4-{[(4-meth­oxy­phen­yl)imino]­meth­yl}phenol monohydrate, (V) (GAPFEK; Mao et al., 2012 ▸). The dihedral angle between the benzene rings in the title compound [72.7 (2)°] is larger than those in compounds (I), (III) and (IV) (49.75–53.63°). Compounds (II) and (V) are almost planar. In all of the compounds, the meth­oxy groups deviate from the plane of aromatic system. There are no C—H⋯π or π–π inter­actions in the crystal structure of the title compound, in contrast to what is observed for compounds (I), (IV) and (V).

Synthesis

4-Hy­droxy-3,5-di­meth­oxy­benzaldehyde (syringaldehyde) (0.05 mol) was added to a mixture of 50 ml of methanol and p-meth­oxy­aniline (PMA) (5 ml, 0.05 mol) and 50 ml of distilled water. The reaction mixture was taken in a clean 250 ml round-bottom flask and stirred well with a magnetic stirrer. It was then refluxed for 7 h. The dark-yellow product that formed was separated by filtration, dried under vacuum and recrystallized from methanol solution upon slow evaporation for two days (yield 65%, m.p. 353–357 K).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. H atoms were positioned geom­etrically and refined using a riding model: O—H = 0.82–0.96 Å and C—H = 0.93–0.96 Å with U iso(H) = 1.2U eq(C) or 1.5U eq(O, Cmethyl).

Table 2

Experimental details

Crystal data
Chemical formula	C16H17NO4
M r	287.30
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	296
a, b, c (Å)	10.4996 (15), 12.4896 (18), 11.8128 (17)
β (°)	107.936 (5)
V (Å3)	1473.8 (4)
Z	4
Radiation type	Mo Kα
μ (mm−1)	0.09
Crystal size (mm)	0.45 × 0.33 × 0.21
Data collection
Diffractometer	Bruker APEXII CCD
No. of measured, independent and observed [I > 2σ(I)] reflections	19289, 2887, 2306
R int	0.035
(sin θ/λ)max (Å−1)	0.617
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.044, 0.116, 1.05
No. of reflections	2887
No. of parameters	194
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.17, −0.21

Computer programs: APEX2 and SAINT (Bruker, 2004 ▸), SHELXS97 (Sheldrick 2008 ▸), SHELXL2017 (Sheldrick, 2015 ▸), ORTEP-3 for Windows (Farrugia, 2012 ▸), Mercury (Macrae et al., 2008 ▸) and PLATON (Spek, 2009 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989018013713/ld2146sup1.cif

Click here for additional data file.

Supporting information file. DOI: 10.1107/S2056989018013713/ld2146Isup3.cml

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989018013713/ld2146Isup3.hkl

CCDC reference: 1843910

Additional supporting information: crystallographic information; 3D view; checkCIF report

C16H17NO4	F(000) = 608
Mr = 287.30	Dx = 1.295 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 10.4996 (15) Å	Cell parameters from 6353 reflections
b = 12.4896 (18) Å	θ = 2.3–28.3°
c = 11.8128 (17) Å	µ = 0.09 mm−1
β = 107.936 (5)°	T = 296 K
V = 1473.8 (4) Å3	Prism, colorless
Z = 4	0.45 × 0.33 × 0.21 mm

Bruker APEXII CCD diffractometer	Rint = 0.035
φ and ω scans	θmax = 26.0°, θmin = 2.3°
19289 measured reflections	h = −12→12
2887 independent reflections	k = −15→15
2306 reflections with I > 2σ(I)	l = −14→14

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.044	H-atom parameters constrained
wR(F2) = 0.116	w = 1/[σ2(Fo2) + (0.0509P)2 + 0.4295P] where P = (Fo2 + 2Fc2)/3
S = 1.05	(Δ/σ)max < 0.001
2887 reflections	Δρmax = 0.17 e Å−3
194 parameters	Δρmin = −0.20 e Å−3

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

	x	y	z	Uiso*/Ueq
O2	0.34000 (12)	0.73324 (9)	0.04196 (10)	0.0465 (3)
H2	0.347012	0.797633	0.056037	0.070*
O3	0.52685 (12)	0.84064 (9)	0.20703 (10)	0.0473 (3)
O1	0.32775 (12)	0.52385 (9)	0.03728 (11)	0.0530 (4)
O4	1.04377 (13)	0.24711 (10)	0.85736 (10)	0.0524 (3)
N1	0.76944 (13)	0.53851 (10)	0.50837 (11)	0.0388 (3)
C10	0.83876 (15)	0.46251 (12)	0.59633 (13)	0.0350 (4)
C15	0.93325 (16)	0.39274 (12)	0.57930 (14)	0.0369 (4)
H15	0.951974	0.392859	0.507304	0.044*
C8	0.61237 (15)	0.56465 (13)	0.31098 (13)	0.0355 (4)
C4	0.42672 (15)	0.56804 (13)	0.12973 (13)	0.0371 (4)
C6	0.53028 (15)	0.73189 (12)	0.21930 (13)	0.0344 (4)
C14	1.00014 (16)	0.32282 (12)	0.66827 (14)	0.0384 (4)
H14	1.064957	0.277361	0.656291	0.046*
C7	0.61974 (15)	0.67549 (13)	0.30970 (13)	0.0361 (4)
H7	0.684472	0.711472	0.369303	0.043*
C9	0.69704 (15)	0.50052 (13)	0.40957 (14)	0.0377 (4)
H9	0.697878	0.426753	0.399120	0.045*
C5	0.43155 (15)	0.67913 (13)	0.13033 (13)	0.0345 (4)
C3	0.51728 (16)	0.51059 (13)	0.21959 (14)	0.0386 (4)
H3	0.514739	0.436151	0.219040	0.046*
C13	0.97179 (16)	0.31969 (13)	0.77481 (14)	0.0380 (4)
C11	0.81296 (18)	0.46051 (15)	0.70406 (15)	0.0486 (5)
H11	0.751385	0.508458	0.717490	0.058*
C12	0.87678 (18)	0.38867 (16)	0.79243 (16)	0.0505 (5)
H12	0.855831	0.386815	0.863378	0.061*
C2	0.6266 (2)	0.90036 (14)	0.29204 (16)	0.0546 (5)
H2B	0.615906	0.975079	0.272312	0.082*
H2C	0.713615	0.877111	0.291596	0.082*
H2D	0.617836	0.889302	0.369713	0.082*
C1	0.3232 (2)	0.41090 (15)	0.02729 (18)	0.0603 (5)
H1A	0.255752	0.390654	−0.044946	0.090*
H1B	0.302110	0.380713	0.094094	0.090*
H1C	0.408703	0.384713	0.025963	0.090*
C16	1.0104 (2)	0.2356 (2)	0.96441 (19)	0.0743 (7)
H16A	0.918409	0.214220	0.945995	0.111*
H16B	1.023357	0.302705	1.006081	0.111*
H16C	1.066751	0.182152	1.013549	0.111*

	U11	U22	U33	U12	U13	U23
O2	0.0477 (7)	0.0351 (6)	0.0389 (6)	0.0019 (5)	−0.0128 (5)	0.0021 (5)
O3	0.0525 (7)	0.0317 (6)	0.0402 (6)	−0.0019 (5)	−0.0114 (5)	0.0026 (5)
O1	0.0521 (7)	0.0372 (7)	0.0488 (7)	−0.0005 (5)	−0.0152 (6)	−0.0056 (5)
O4	0.0602 (8)	0.0525 (8)	0.0453 (7)	0.0195 (6)	0.0174 (6)	0.0221 (6)
N1	0.0403 (7)	0.0353 (7)	0.0342 (7)	0.0050 (6)	0.0017 (6)	0.0049 (6)
C10	0.0353 (8)	0.0315 (8)	0.0324 (8)	−0.0008 (6)	0.0019 (6)	0.0039 (6)
C15	0.0442 (9)	0.0333 (8)	0.0314 (8)	0.0013 (7)	0.0091 (7)	0.0009 (6)
C8	0.0328 (8)	0.0371 (8)	0.0322 (8)	0.0034 (6)	0.0036 (6)	0.0025 (6)
C4	0.0341 (8)	0.0375 (9)	0.0337 (8)	−0.0001 (7)	0.0016 (6)	−0.0034 (6)
C6	0.0354 (8)	0.0323 (8)	0.0308 (8)	−0.0002 (6)	0.0034 (6)	0.0008 (6)
C14	0.0418 (9)	0.0317 (8)	0.0413 (9)	0.0055 (7)	0.0121 (7)	0.0022 (7)
C7	0.0339 (8)	0.0380 (9)	0.0291 (8)	−0.0018 (7)	−0.0011 (6)	−0.0006 (6)
C9	0.0368 (8)	0.0333 (8)	0.0389 (9)	0.0028 (7)	0.0056 (7)	0.0049 (7)
C5	0.0319 (8)	0.0373 (9)	0.0285 (8)	0.0033 (6)	0.0007 (6)	0.0030 (6)
C3	0.0402 (9)	0.0314 (8)	0.0394 (9)	0.0030 (7)	0.0052 (7)	0.0017 (7)
C13	0.0378 (9)	0.0348 (9)	0.0380 (9)	0.0031 (7)	0.0066 (7)	0.0080 (7)
C11	0.0460 (10)	0.0548 (11)	0.0458 (10)	0.0201 (8)	0.0156 (8)	0.0111 (8)
C12	0.0529 (11)	0.0624 (12)	0.0400 (9)	0.0154 (9)	0.0198 (8)	0.0145 (8)
C2	0.0591 (12)	0.0363 (10)	0.0509 (11)	−0.0115 (8)	−0.0089 (9)	0.0027 (8)
C1	0.0658 (13)	0.0427 (11)	0.0568 (11)	−0.0089 (9)	−0.0042 (10)	−0.0113 (9)
C16	0.0816 (16)	0.0896 (17)	0.0569 (13)	0.0299 (13)	0.0291 (11)	0.0395 (12)

O1—C2i	3.159 (2)	C6—C7	1.379 (2)
O2—C5	1.3610 (17)	C6—C5	1.394 (2)
O2—H2	0.8200	C14—C13	1.380 (2)
O3—C6	1.3652 (19)	C14—H14	0.9300
O3—C2	1.4193 (19)	C7—H7	0.9300
O1—C4	1.3704 (18)	C9—H9	0.9300
O1—C1	1.415 (2)	C3—H3	0.9300
O4—C13	1.3748 (18)	C13—C12	1.382 (2)
O4—C16	1.420 (2)	C11—C12	1.383 (2)
N1—C9	1.2722 (19)	C11—H11	0.9300
N1—C10	1.4299 (19)	C12—H12	0.9300
C10—C11	1.380 (2)	C2—H2B	0.9600
C10—C15	1.381 (2)	C2—H2C	0.9600
C15—C14	1.381 (2)	C2—H2D	0.9600
C15—H15	0.9300	C1—H1A	0.9600
C8—C7	1.387 (2)	C1—H1B	0.9600
C8—C3	1.398 (2)	C1—H1C	0.9600
C8—C9	1.466 (2)	C16—H16A	0.9600
C4—C3	1.387 (2)	C16—H16B	0.9600
C4—C5	1.388 (2)	C16—H16C	0.9600
C5—O2—H2	109.5	C4—C5—C6	119.60 (13)
C6—O3—C2	117.27 (12)	C4—C3—C8	119.96 (15)
C4—O1—C1	117.75 (13)	C4—C3—H3	120.0
C13—O4—C16	117.76 (14)	C8—C3—H3	120.0
C9—N1—C10	116.47 (13)	O4—C13—C14	116.08 (14)
C11—C10—C15	118.47 (14)	O4—C13—C12	124.69 (15)
C11—C10—N1	118.78 (14)	C14—C13—C12	119.22 (14)
C15—C10—N1	122.73 (14)	C10—C11—C12	121.36 (16)
C14—C15—C10	120.54 (15)	C10—C11—H11	119.3
C14—C15—H15	119.7	C12—C11—H11	119.3
C10—C15—H15	119.7	C13—C12—C11	119.69 (16)
C7—C8—C3	120.18 (14)	C13—C12—H12	120.2
C7—C8—C9	122.12 (14)	C11—C12—H12	120.2
C3—C8—C9	117.62 (14)	O3—C2—H2B	109.5
O1—C4—C3	125.06 (15)	O3—C2—H2C	109.5
O1—C4—C5	115.09 (13)	H2B—C2—H2C	109.5
C3—C4—C5	119.85 (14)	O3—C2—H2D	109.5
O3—C6—C7	125.44 (13)	H2B—C2—H2D	109.5
O3—C6—C5	113.65 (13)	H2C—C2—H2D	109.5
C7—C6—C5	120.91 (14)	O1—C1—H1A	109.5
C13—C14—C15	120.67 (15)	O1—C1—H1B	109.5
C13—C14—H14	119.7	H1A—C1—H1B	109.5
C15—C14—H14	119.7	O1—C1—H1C	109.5
C6—C7—C8	119.44 (14)	H1A—C1—H1C	109.5
C6—C7—H7	120.3	H1B—C1—H1C	109.5
C8—C7—H7	120.3	O4—C16—H16A	109.5
N1—C9—C8	124.73 (15)	O4—C16—H16B	109.5
N1—C9—H9	117.6	H16A—C16—H16B	109.5
C8—C9—H9	117.6	O4—C16—H16C	109.5
O2—C5—C4	118.44 (13)	H16A—C16—H16C	109.5
O2—C5—C6	121.96 (14)	H16B—C16—H16C	109.5
C9—N1—C10—C11	−120.05 (18)	C3—C4—C5—C6	2.1 (2)
C9—N1—C10—C15	61.7 (2)	O3—C6—C5—O2	−1.2 (2)
C11—C10—C15—C14	0.0 (2)	C7—C6—C5—O2	178.26 (15)
N1—C10—C15—C14	178.20 (15)	O3—C6—C5—C4	177.70 (14)
C1—O1—C4—C3	−4.9 (3)	C7—C6—C5—C4	−2.8 (2)
C1—O1—C4—C5	175.89 (16)	O1—C4—C3—C8	−178.61 (15)
C2—O3—C6—C7	2.4 (2)	C5—C4—C3—C8	0.5 (2)
C2—O3—C6—C5	−178.17 (15)	C7—C8—C3—C4	−2.4 (2)
C10—C15—C14—C13	1.4 (2)	C9—C8—C3—C4	174.26 (15)
O3—C6—C7—C8	−179.66 (15)	C16—O4—C13—C14	−175.25 (18)
C5—C6—C7—C8	0.9 (2)	C16—O4—C13—C12	5.6 (3)
C3—C8—C7—C6	1.7 (2)	C15—C14—C13—O4	179.86 (15)
C9—C8—C7—C6	−174.84 (15)	C15—C14—C13—C12	−1.0 (3)
C10—N1—C9—C8	176.30 (14)	C15—C10—C11—C12	−1.8 (3)
C7—C8—C9—N1	10.4 (3)	N1—C10—C11—C12	179.89 (16)
C3—C8—C9—N1	−166.23 (16)	O4—C13—C12—C11	178.25 (17)
O1—C4—C5—O2	0.2 (2)	C14—C13—C12—C11	−0.8 (3)
C3—C4—C5—O2	−178.98 (14)	C10—C11—C12—C13	2.2 (3)
O1—C4—C5—C6	−178.72 (14)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···N1i	0.82	2.21	2.9415 (18)	149
C7—H7···O2ii	0.93	2.29	3.2043 (18)	167