The effect of molecular planarity on crystal non-centrosymmetry in benzyl­idene–aniline derivatives

In the title compound, N-(2-methoxy­phenyl)-4-nitro­benzyli­deneamine, C₁₄H₁₂N₂O₃, the two phenyl rings make a dihedral angle of 48.0 (2)° and the nitro group is at an angle of 6.5 (1)° with respect to its attached phenyl ring. In the crystal structure, mol­ecules are related as centrosymmetric pairs through π–π interactions and are further connected through strong C—H...O hydrogen bonds [C...O 3.4259 (17) Å and C—H...O 167°], forming molecular stacks along [100]. These stacks associate further through longer C—H...O interactions, forming two-dimensional networks. In the c direction, there are only weak van der Waals interactions. The relationship between the molecular planarity and its centrosymmetry is also briefly described.

S1. Comment

A number of benzylidene–aniline derivatives (BA) (Tetsuya et al., 1990; Sun et al., 1994; Qi et al., 1996) have been shown to be potential crystalline compounds for second harmonic generation (SHG). For an SHG crystal, the molecule should have a relatively large dipole moment, but the crystal should not have a centre of symmetry. Since dipole–dipole interactions between molecules favours antiparallel packing resulting in a centrosymmetric crystal, one should study the factors that can weaken the above tendency while not greatly reducing the molecular dipole. According to our preliminary study (Peng, 2001) on the BA crystal whose data were retrieved from the Cambridge Structural Database (2001), the molecular planarity is one of the important factors. From the data presented in Table 2, a strong correlation can be noted indicating that the more planar molecules have a greater possibility of crystallizing in a non-centrosymmetric space group.

During our systematic research on the crystal engineering of BA systems, we synthesized the title compound, (I), and describe its crystal structure here. The two phenyl rings make a dihedral angle of 48.0 (2)° with one another and the nitro group is at an angle of 6.5 (2)° with respect to its attached aromatic ring. Because the OCH₃ group is not sterically small and as it is positioned ortho to the central linkage, the title molecule is not especially planar, which may be a primary reason why it crystallized in a centrosymmetric space group.

In (I), the molecules are paired by strong π–π-stacking interactions (symmetry code: -x, -y + 2, -z). The shortest distances between the ring planes and their centroids, respectively, are 3.46 (1) and 3.62 (1) Å. The packing potential energies (PPE), calculated using OPEC (Gavezzotti, 1983), for the whole crystal and the above molecular pair are -148.7 and -26.4 kJ mol^-1, respectively.

The pairs are connected by strong hydrogen bonds C10—H10···O3 (Table 2; Krishnamohan & Desiraju, 1994). The aforementioned interactions link the molecules stacked along [100] into chains. The chains are further connected through weak C9—H9···O2 hydrogen bonds (Table 3), forming two-dimensional networks. In the third direction, [001], there are only relatively weak interactions, which may explain the plate-like crystal habit.

S2. Experimental

4-Nitrophenylaldehyde (1.51 g, 10 mmol) and 2-methoxyphenylamine (1.13 g, 10 mmol) in ethanol (10 ml) were heated at 363 K with stirring for 30 min. After cooling to room temperature for 15 min, the product was separated and recrystallized from ethanol twice (m.p. 430 K), and the yellow square-plate crystal used for analysis was grown from toluene. Spectroscopic analysis (IR): 1645, 1587, 1520, 864, 752, 727 cm^-1. Elemental analysis, found: C 58.97, H 4.98, N 10.66%; C₁₄H₁₂N₂O₃ requires: C 59.02, H 5.07, N 11.58%.

S3. Refinement

H atoms were placed in calculated positions and refined as riding (C—H = 0.93 and 0.96 Å).

Computing details

Data collection: XSCANS (Siemens, 1994); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 1997a); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997b); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997b); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The molecular structure of (I) showing 50% probability displacement ellipsoids.
	Fig. 2. Packing diagram for (I) viewed down the a axis.

N-(2-methoxyphenyl)-4-nitrophenylimine

Crystal data

C14H12N2O3	F(000) = 536
Mr = 256.26	Dx = 1.336 Mg m^−3 Dm = 1.330 Mg m^−3 Dm measured by floatation
Monoclinic, P21/c	Melting point: 430 K
Hall symbol: -p_2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 7.2703 (6) Å	Cell parameters from 22 reflections
b = 7.2963 (8) Å	θ = 4.2–12.8°
c = 24.086 (3) Å	µ = 0.10 mm^−1
β = 94.517 (8)°	T = 295 K
V = 1273.7 (2) Å^3	Square plate, yellow
Z = 4	0.50 × 0.48 × 0.46 mm

Data collection

Siemens P4 diffractometer	Rint = 0.023
Radiation source: normal-focus sealed tube	θmax = 25.5°, θmin = 1.7°
Graphite monochromator	h = 0→8
ω scans	k = 0→8
2876 measured reflections	l = −29→29
2372 independent reflections	3 standard reflections every 97 reflections
1662 reflections with I > 2σ(I)	intensity decay: 6%

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)] = 0.040	H-atom parameters constrained
wR(F^2) = 0.108	w = 1/[σ^2(Fo^2) + (0.0619P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max < 0.001
2372 reflections	Δρmax = 0.19 e Å^−3
174 parameters	Δρmin = −0.24 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.036 (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	0.14736 (15)	0.40162 (15)	0.21935 (4)	0.0636 (3)
O2	−0.22348 (18)	1.44504 (18)	0.01444 (6)	0.0866 (4)
O3	−0.41247 (19)	1.22499 (18)	−0.00185 (7)	0.0964 (5)
N1	0.21159 (17)	0.62637 (16)	0.13563 (5)	0.0497 (3)
N2	−0.2667 (2)	1.2858 (2)	0.01814 (6)	0.0613 (4)
C1	0.3174 (2)	0.38716 (19)	0.19999 (6)	0.0499 (4)
C2	0.4523 (3)	0.2662 (2)	0.22012 (7)	0.0650 (5)
H2	0.4280	0.1839	0.2481	0.078*
C3	0.6231 (3)	0.2668 (3)	0.19894 (8)	0.0749 (6)
H3	0.7132	0.1851	0.2130	0.090*
C4	0.6620 (3)	0.3858 (3)	0.15748 (8)	0.0719 (5)
H4	0.7780	0.3861	0.1437	0.086*
C5	0.5258 (2)	0.5059 (2)	0.13624 (6)	0.0605 (4)
H5	0.5500	0.5846	0.1073	0.073*
C6	0.3551 (2)	0.5101 (2)	0.15747 (6)	0.0470 (4)
C7	0.2488 (2)	0.7927 (2)	0.12665 (6)	0.0496 (4)
H7	0.3667	0.8358	0.1373	0.059*
C8	0.1131 (2)	0.91969 (19)	0.10013 (6)	0.0458 (4)
C9	−0.0643 (2)	0.8616 (2)	0.08222 (6)	0.0539 (4)
H9	−0.0986	0.7409	0.0882	0.065*
C10	−0.1890 (2)	0.9804 (2)	0.05583 (6)	0.0548 (4)
H10	−0.3072	0.9413	0.0437	0.066*
C11	−0.1351 (2)	1.1588 (2)	0.04774 (6)	0.0480 (4)
C12	0.0377 (2)	1.2217 (2)	0.06513 (6)	0.0543 (4)
H12	0.0703	1.3431	0.0595	0.065*
C13	0.1619 (2)	1.10074 (19)	0.09119 (6)	0.0524 (4)
H13	0.2800	1.1409	0.1030	0.063*
C14	0.1085 (3)	0.2874 (3)	0.26450 (9)	0.0992 (7)
H14A	0.1140	0.1614	0.2533	0.119*
H14B	−0.0127	0.3144	0.2754	0.119*
H14C	0.1978	0.3090	0.2953	0.119*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0629 (7)	0.0636 (7)	0.0642 (7)	−0.0021 (6)	0.0043 (6)	0.0155 (6)
O2	0.0877 (10)	0.0574 (8)	0.1132 (11)	0.0082 (7)	−0.0010 (8)	0.0269 (7)
O3	0.0717 (9)	0.0817 (10)	0.1293 (12)	0.0042 (7)	−0.0341 (9)	0.0131 (8)
N1	0.0573 (8)	0.0447 (7)	0.0463 (7)	0.0038 (6)	−0.0011 (6)	0.0023 (6)
N2	0.0623 (9)	0.0585 (9)	0.0625 (8)	0.0096 (8)	0.0022 (7)	0.0069 (7)
C1	0.0592 (10)	0.0435 (8)	0.0454 (8)	0.0003 (7)	−0.0061 (7)	−0.0027 (7)
C2	0.0816 (12)	0.0539 (10)	0.0572 (10)	0.0103 (9)	−0.0093 (9)	0.0064 (8)
C3	0.0807 (13)	0.0697 (12)	0.0713 (12)	0.0297 (10)	−0.0122 (10)	−0.0023 (10)
C4	0.0651 (11)	0.0824 (13)	0.0683 (11)	0.0209 (10)	0.0062 (9)	−0.0108 (10)
C5	0.0694 (11)	0.0626 (10)	0.0498 (9)	0.0096 (9)	0.0072 (8)	−0.0012 (8)
C6	0.0551 (9)	0.0437 (8)	0.0406 (7)	0.0050 (7)	−0.0057 (6)	−0.0042 (6)
C7	0.0546 (9)	0.0497 (9)	0.0435 (8)	0.0008 (7)	−0.0020 (7)	−0.0016 (7)
C8	0.0542 (9)	0.0435 (8)	0.0392 (7)	0.0002 (7)	0.0000 (7)	−0.0024 (6)
C9	0.0599 (10)	0.0417 (8)	0.0593 (9)	−0.0044 (7)	0.0002 (8)	0.0044 (7)
C10	0.0499 (9)	0.0543 (9)	0.0592 (10)	−0.0034 (7)	−0.0027 (7)	0.0015 (8)
C11	0.0563 (9)	0.0460 (8)	0.0414 (7)	0.0065 (7)	0.0025 (7)	0.0009 (7)
C12	0.0647 (10)	0.0393 (8)	0.0581 (9)	−0.0030 (8)	0.0003 (8)	0.0017 (7)
C13	0.0547 (9)	0.0461 (9)	0.0547 (9)	−0.0043 (7)	−0.0063 (7)	−0.0023 (7)
C14	0.0918 (15)	0.1074 (17)	0.0997 (15)	−0.0120 (13)	0.0151 (12)	0.0452 (13)

Geometric parameters (Å, º)

O1—C1	1.3595 (17)	C5—H5	0.9300
O1—C14	1.416 (2)	C7—C8	1.463 (2)
O2—N2	1.2087 (17)	C7—H7	0.9300
O3—N2	1.2131 (17)	C8—C13	1.3890 (19)
N1—C7	1.2661 (18)	C8—C9	1.393 (2)
N1—C6	1.4136 (18)	C9—C10	1.374 (2)
N2—C11	1.4748 (19)	C9—H9	0.9300
C1—C2	1.378 (2)	C10—C11	1.378 (2)
C1—C6	1.404 (2)	C10—H10	0.9300
C2—C3	1.379 (3)	C11—C12	1.372 (2)
C2—H2	0.9300	C12—C13	1.378 (2)
C3—C4	1.369 (3)	C12—H12	0.9300
C3—H3	0.9300	C13—H13	0.9300
C4—C5	1.390 (2)	C14—H14A	0.9600
C4—H4	0.9300	C14—H14B	0.9600
C5—C6	1.379 (2)	C14—H14C	0.9600
C1—O1—C14	117.36 (14)	C8—C7—H7	118.8
C7—N1—C6	118.54 (13)	C13—C8—C9	118.86 (13)
O2—N2—O3	123.12 (15)	C13—C8—C7	119.87 (13)
O2—N2—C11	118.50 (15)	C9—C8—C7	121.25 (13)
O3—N2—C11	118.37 (14)	C10—C9—C8	120.85 (14)
O1—C1—C2	124.75 (14)	C10—C9—H9	119.6
O1—C1—C6	115.80 (13)	C8—C9—H9	119.6
C2—C1—C6	119.43 (15)	C9—C10—C11	118.46 (14)
C1—C2—C3	120.27 (16)	C9—C10—H10	120.8
C1—C2—H2	119.9	C11—C10—H10	120.8
C3—C2—H2	119.9	C12—C11—C10	122.46 (14)
C4—C3—C2	121.04 (16)	C12—C11—N2	118.76 (13)
C4—C3—H3	119.5	C10—C11—N2	118.76 (14)
C2—C3—H3	119.5	C11—C12—C13	118.45 (14)
C3—C4—C5	119.08 (17)	C11—C12—H12	120.8
C3—C4—H4	120.5	C13—C12—H12	120.8
C5—C4—H4	120.5	C12—C13—C8	120.90 (14)
C6—C5—C4	120.89 (16)	C12—C13—H13	119.5
C6—C5—H5	119.6	C8—C13—H13	119.5
C4—C5—H5	119.6	O1—C14—H14A	109.5
C5—C6—C1	119.27 (14)	O1—C14—H14B	109.5
C5—C6—N1	122.30 (14)	H14A—C14—H14B	109.5
C1—C6—N1	118.31 (13)	O1—C14—H14C	109.5
N1—C7—C8	122.40 (14)	H14A—C14—H14C	109.5
N1—C7—H7	118.8	H14B—C14—H14C	109.5
C14—O1—C1—C2	1.9 (2)	N1—C7—C8—C13	−179.83 (14)
C14—O1—C1—C6	−176.30 (15)	N1—C7—C8—C9	−1.5 (2)
O1—C1—C2—C3	−177.67 (15)	C13—C8—C9—C10	0.4 (2)
C6—C1—C2—C3	0.4 (2)	C7—C8—C9—C10	−177.99 (14)
C1—C2—C3—C4	−0.4 (3)	C8—C9—C10—C11	−0.4 (2)
C2—C3—C4—C5	−0.7 (3)	C9—C10—C11—C12	−0.2 (2)
C3—C4—C5—C6	1.9 (3)	C9—C10—C11—N2	178.43 (13)
C4—C5—C6—C1	−1.9 (2)	O2—N2—C11—C12	−6.3 (2)
C4—C5—C6—N1	−177.91 (14)	O3—N2—C11—C12	172.93 (15)
O1—C1—C6—C5	179.00 (13)	O2—N2—C11—C10	175.07 (15)
C2—C1—C6—C5	0.7 (2)	O3—N2—C11—C10	−5.7 (2)
O1—C1—C6—N1	−4.85 (19)	C10—C11—C12—C13	0.6 (2)
C2—C1—C6—N1	176.89 (13)	N2—C11—C12—C13	−177.98 (13)
C7—N1—C6—C5	−46.8 (2)	C11—C12—C13—C8	−0.6 (2)
C7—N1—C6—C1	137.14 (15)	C9—C8—C13—C12	0.1 (2)
C6—N1—C7—C8	175.13 (12)	C7—C8—C13—C12	178.48 (14)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C10—H10···O3^i	0.93	2.51	3.4259 (17)	167
C12—H12···O2^ii	0.93	2.67	3.4376 (19)	141
C9—H9···O2^iii	0.93	2.90	3.5977 (19)	133
C12—H12···N1^iv	0.93	2.90	3.5861 (17)	132

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