Racemic 3,5-di­chloro-2-{[(1-phenyl­ethyl)­imino]­methyl}phenol

The title compound, (RS)-3,5-di­chloro-2-{[(1-phenyl­ethyl)­imino]­methyl}phenol, C₁₅H₁₃Cl₂NO, was synthesized from racemic 1-phenyl­ethyl­amine and 3,5-di­chloro­salicyl­aldehyde. The π-conjugate system around the imine group is essentially planar in the phenol–imine tautomer. Intramolecular O...N hydrogen-bond and intermolecular C—H...π interactions are present in the crystal structure.

S1. Comment

Schiff bases are used extensively as ligands in the field of coordination chemistry (Yamada, 1999). The complexes formed are interesting, for example in structural phase transitions (Akitsu & Einaga, 2004), as homogeneous catalysts (Akitsu et al., 2004), and for their other chemical and physical properties. They have potential as sophisticated chiral building blocks in the synthesis of optical materials (Evans & Luneau, 2002), as well as in conventional stereochemistry (Sakiyama et al., 1990). In order to clarify the relationship between structure and function in these organic ligands, which exhibit both tautomerism and photochromism (Hadjoudis et al., 1987) in their metal complexes, an X-ray structure determination of the title compound, (I), has been carried out. \sch

The molecule of (I) adopts an E configuration with respect to the imine C═N double bond, with a C6—C7—N1—C8 torsion angle of 176.2 (3)° (Fig. 1). Thus, the π-conjugate system around the imine group is essentially planar. This is a common feature for the related compounds, such as 2-benzylamino-3-(2-hydroxybenzylidene)aminobenzofuran, which have stereochemically bulky groups (Bossio et al., 1991). The maximum deviation from the least-squares mean plane of atoms O1/C1/C6/C7/N1, incorporating the bidentate chelate sites, is only 0.018 (4) Å, for atom C7.

In general, Schiff base compounds exhibit tautomerization between keto-amine and phenol-imine tautomers by H-atom transfer, with the C—O bond distance being longer in the latter form. The C1—O1 bond distance in (I) is 1.347 (3) Å, and the C7═N1 and N1—C8 bond distances are 1.271 (5) and 1.478 (4) Å, respectively. The geometric parameters for (I) (Table 1) agree with the corresponding values for analogous Schiff base compounds containing the 1-phenylethylamine moiety, with the usual C═N and C—N bond distances being around 1.27 and 1.45 Å, respectively (Senn & Nowacki, 1977; Antonov et al., 1995; Liu et al., 1997). Compound (I) is therefore in the stable phenol-imine tautomeric form with insignificant changes in the intramolecular geometry, even in the presence of an electron-withdrawing Cl group. As (I) crystallizes in a (racemic) centrosymmetric space group, there is no spontaneous resolution. The two six-membered aromatic rings, C1—C6 and C9—C14, form a dihedral angle of 76.11 (9)°.

The molecular planarity of (I) is stabilized by an intramolecular N1···O1 hydrogen bond of 2.601 (3) Å (Table 2), with the parent N1···O1 distance being shorter than the sums of the relevant van der Waals radii (Bondi, 1964). The corresponding distances are in the range 2.58–2.62 Å for other N-salicylideneanilines (Inabe et al., 1989, 1991, 1994). Unfortunately, we could not assign the hydroxyl H atom (H13) bonded to atom O1 directly from the difference Fourier map, so we located it at a reasonable position (O—H = 0.985 Å) and constrained it using a riding model.

The crystal packing of (I) (Fig. 2) involves a weak C—H···π intermolecular C3—H1···Cg1 interaction, yielding centrosymmetric dimers with H1···Cg1 2.82 Å, C3···Cg1 3.752 (3) Å and C3—H1···Cg1 167° [Cg1 is the centroid of ring C9—C14 at (2 − x,2 − y,1 − z)].

We also observed photochromism of (I) in the solid state at 8 K. The imine band of the IR spectrum appeared initially at 1635 cm⁻¹. Irradiation with UV light resulted in a shift of this band to 1630 cm⁻¹, and the spectroscopic features were recovered after irradiation with visible light.

S2. Experimental

Reaction of equimolar quantities of 1-phenylethylamine and 3,5-dichlorosalciylaldehyde in methanol at room temperature overnight gave rise to the brown compound, (I). Prismatic crystals were grown from the resulting solution over a period of several days. IR (KBr): 1635 cm⁻¹ (imine band).

S3. Refinement

H atoms were placed in calculated positions, with C—H = N—H = 0.95 Å and O—H = 0.99 Å, and included in the final cycles of refinement using a riding model, with U_iso(H) = 1.2U_eq(parent atom). The C atoms of the phenyl groups (C1—C6 and C9—C14) were treated as rigid groups of anisotropic atoms.

Computing details

Data collection: WinAFC Diffractometer Control Software (Rigaku, 1999); cell refinement: WinAFC Diffractometer Control Software; data reduction: TEXSAN (Molecular Structure Corporation, 2001); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: TEXSAN.

Figures

	Fig. 1. The molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A molecular packing diagram for (I), showing the centrosymmetric dimers. Atoms marked with an asterisk (*) are at the symmetry position (2 − x, 2 − y, 1 − z).

3,5-dichloro-2-{[(1-phenylethyl)imino]methyl}phenol

Crystal data

C15H13Cl2NO	F(000) = 1216.0
Mr = 294.16	Dx = 1.357 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.7107 Å
Hall symbol: -C 2yc	Cell parameters from 25 reflections
a = 21.395 (8) Å	θ = 10.0–12.3°
b = 9.463 (5) Å	µ = 0.44 mm^−1
c = 15.571 (7) Å	T = 298 K
β = 113.99 (3)°	Prismatic, brown
V = 2880 (2) Å^3	0.60 × 0.50 × 0.50 mm
Z = 8

Data collection

Rigaku AFC-7R diffractometer	Rint = 0.030
ω/2θ scans	θmax = 27.5°
Absorption correction: ψ scan (North et al., 1968)	h = −25→27
Tmin = 0.768, Tmax = 0.802	k = 0→12
3867 measured reflections	l = −20→8
3323 independent reflections	3 standard reflections every 150 reflections
1468 reflections with I > 2σ(I)	intensity decay: 0.5%

Refinement

Refinement on F^2	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.051	w = 1/[σ^2(Fo^2) + (0.064P)^2 + 1.9396P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.180	(Δ/σ)max < 0.001
S = 1.02	Δρmax = 0.23 e Å^−3
1468 reflections	Δρmin = −0.25 e Å^−3
149 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cl1	1.15758 (4)	0.9105 (1)	0.56244 (8)	0.0956 (4)
Cl2	1.03127 (6)	1.3908 (1)	0.3983 (1)	0.1200 (5)
O1	1.0345 (1)	0.7741 (3)	0.4275 (2)	0.0806 (7)
N1	0.9104 (1)	0.7751 (3)	0.2979 (2)	0.0712 (8)
C1	1.0328 (1)	0.9157 (2)	0.4183 (2)	0.0609 (8)
C2	1.08891 (8)	0.9932 (2)	0.4777 (1)	0.0659 (8)
C3	1.08869 (9)	1.1397 (2)	0.4709 (1)	0.0690 (9)
C4	1.0323 (1)	1.2087 (2)	0.4047 (2)	0.0737 (9)
C5	0.97617 (9)	1.1312 (2)	0.3454 (1)	0.0749 (10)
C6	0.97640 (8)	0.9847 (2)	0.3521 (1)	0.0633 (8)
C7	0.9151 (2)	0.9082 (4)	0.2914 (2)	0.0734 (9)
C8	0.8449 (2)	0.7071 (4)	0.2379 (2)	0.080 (1)
C9	0.8115 (1)	0.6553 (3)	0.3006 (1)	0.0624 (8)
C10	0.7560 (1)	0.7300 (2)	0.3023 (2)	0.079 (1)
C11	0.7262 (1)	0.6888 (3)	0.3627 (2)	0.100 (1)
C12	0.7518 (2)	0.5728 (3)	0.4214 (2)	0.099 (1)
C13	0.8072 (2)	0.4981 (2)	0.4196 (2)	0.092 (1)
C14	0.8370 (1)	0.5393 (2)	0.3592 (2)	0.0771 (10)
C15	0.8592 (2)	0.5948 (5)	0.1802 (3)	0.111 (2)
H1	1.1271	1.1925	0.5115	0.0831*
H2	0.9377	1.1783	0.3002	0.0904*
H3	0.8778	0.9594	0.2463	0.0889*
H4	0.8161	0.7759	0.1963	0.0953*
H5	0.7384	0.8091	0.2621	0.0958*
H6	0.6882	0.7397	0.3637	0.1199*
H7	0.7315	0.5447	0.4627	0.1175*
H8	0.8247	0.4188	0.4598	0.1113*
H9	0.8749	0.4884	0.3582	0.0929*
H10	0.8178	0.5514	0.1396	0.1342*
H11	0.8814	0.6353	0.1442	0.1342*
H12	0.8886	0.5244	0.2211	0.1342*
H13	0.9911	0.7383	0.3795	0.0972*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0536 (5)	0.1069 (8)	0.1062 (8)	0.0065 (5)	0.0119 (4)	0.0161 (6)
Cl2	0.1077 (9)	0.0828 (8)	0.134 (1)	−0.0157 (6)	0.0125 (7)	0.0225 (7)
O1	0.065 (1)	0.080 (2)	0.093 (2)	−0.003 (1)	0.028 (1)	−0.004 (1)
N1	0.065 (2)	0.087 (2)	0.060 (2)	−0.017 (2)	0.024 (1)	−0.008 (2)
C1	0.057 (2)	0.071 (2)	0.063 (2)	−0.004 (2)	0.034 (1)	0.000 (2)
C2	0.048 (2)	0.087 (2)	0.065 (2)	0.000 (2)	0.026 (2)	0.001 (2)
C3	0.054 (2)	0.091 (3)	0.062 (2)	−0.014 (2)	0.023 (2)	−0.002 (2)
C4	0.069 (2)	0.081 (2)	0.067 (2)	−0.013 (2)	0.023 (2)	0.007 (2)
C5	0.068 (2)	0.092 (3)	0.057 (2)	−0.006 (2)	0.018 (2)	0.013 (2)
C6	0.058 (2)	0.083 (2)	0.049 (2)	−0.008 (2)	0.022 (1)	−0.001 (2)
C7	0.066 (2)	0.099 (3)	0.049 (2)	−0.013 (2)	0.016 (1)	0.001 (2)
C8	0.069 (2)	0.099 (3)	0.059 (2)	−0.020 (2)	0.014 (2)	−0.009 (2)
C9	0.062 (2)	0.071 (2)	0.047 (2)	−0.014 (2)	0.014 (1)	−0.008 (2)
C10	0.067 (2)	0.087 (3)	0.069 (2)	0.000 (2)	0.012 (2)	−0.007 (2)
C11	0.067 (2)	0.140 (4)	0.088 (3)	−0.011 (2)	0.027 (2)	−0.029 (3)
C12	0.103 (3)	0.121 (4)	0.079 (3)	−0.037 (3)	0.045 (3)	−0.017 (3)
C13	0.119 (3)	0.081 (3)	0.062 (2)	−0.017 (3)	0.022 (2)	−0.002 (2)
C14	0.079 (2)	0.082 (2)	0.066 (2)	−0.001 (2)	0.025 (2)	−0.010 (2)
C15	0.107 (3)	0.156 (4)	0.086 (3)	−0.047 (3)	0.055 (3)	−0.052 (3)

Geometric parameters (Å, º)

Cl1—C2	1.714 (2)	C8—C15	1.502 (7)
Cl2—C4	1.726 (2)	C8—H4	0.950
O1—C1	1.347 (3)	C9—C10	1.390 (4)
O1—H13	0.985	C9—C14	1.390 (3)
N1—C7	1.271 (5)	C10—C11	1.390 (4)
N1—C8	1.478 (4)	C10—H5	0.950
C1—C2	1.390 (2)	C11—C12	1.390 (4)
C1—C6	1.390 (2)	C11—H6	0.950
C2—C3	1.390 (3)	C12—C13	1.390 (5)
C3—C4	1.390 (3)	C12—H7	0.950
C3—H1	0.950	C13—C14	1.390 (4)
C4—C5	1.390 (3)	C13—H8	0.950
C5—C6	1.390 (3)	C14—H9	0.950
C5—H2	0.950	C15—H10	0.950
C6—C7	1.460 (4)	C15—H11	0.950
C7—H3	0.950	C15—H12	0.950
C8—C9	1.507 (5)
C1—O1—H13	106.6	C9—C8—H4	108.5
C7—N1—C8	117.8 (3)	C15—C8—H4	108.1
O1—C1—C2	118.4 (2)	C8—C9—C10	118.7 (2)
O1—C1—C6	121.6 (2)	C8—C9—C14	121.3 (2)
C2—C1—C6	120.0 (2)	C10—C9—C14	120.0 (2)
Cl1—C2—C1	120.7 (2)	C9—C10—C11	120.0 (2)
Cl1—C2—C3	119.3 (1)	C9—C10—H5	120.1
C1—C2—C3	120.0 (1)	C11—C10—H5	119.9
C2—C3—C4	120.0 (2)	C10—C11—C12	120.0 (3)
C2—C3—H1	119.9	C10—C11—H6	120.0
C4—C3—H1	120.1	C12—C11—H6	120.0
Cl2—C4—C3	119.9 (1)	C11—C12—C13	120.0 (3)
Cl2—C4—C5	120.0 (1)	C11—C12—H7	120.0
C3—C4—C5	120.0 (2)	C13—C12—H7	120.0
C4—C5—C6	120.0 (2)	C12—C13—C14	120.0 (2)
C4—C5—H2	120.0	C12—C13—H8	120.0
C6—C5—H2	120.0	C14—C13—H8	120.0
C1—C6—C5	120.0 (1)	C9—C14—C13	120.0 (2)
C1—C6—C7	121.9 (2)	C9—C14—H9	120.0
C5—C6—C7	118.1 (2)	C13—C14—H9	120.0
N1—C7—C6	121.3 (3)	C8—C15—H10	110.0
N1—C7—H3	119.5	C8—C15—H11	109.9
C6—C7—H3	119.2	C8—C15—H12	109.4
N1—C8—C9	108.0 (3)	H10—C15—H11	109.7
N1—C8—C15	108.4 (3)	H10—C15—H12	109.0
N1—C8—H4	108.6	H11—C15—H12	108.8
C9—C8—C15	115.0 (3)
Cl1—C2—C1—O1	−1.7 (4)	C3—C2—C1—C6	0.0 (4)
Cl1—C2—C1—C6	177.7 (2)	C3—C4—C5—C6	0.0 (4)
Cl1—C2—C3—C4	−177.7 (2)	C4—C5—C6—C7	177.2 (3)
Cl2—C4—C3—C2	178.5 (2)	C6—C7—N1—C8	176.2 (3)
Cl2—C4—C5—C6	−178.5 (2)	C7—N1—C8—C9	−111.1 (4)
O1—C1—C2—C3	−179.3 (2)	C7—N1—C8—C15	123.6 (4)
O1—C1—C6—C5	179.3 (3)	C8—C9—C10—C11	−176.9 (2)
O1—C1—C6—C7	2.3 (4)	C8—C9—C14—C13	176.8 (2)
N1—C7—C6—C1	1.3 (5)	C9—C10—C11—C12	0.0 (3)
N1—C7—C6—C5	−175.8 (3)	C9—C14—C13—C12	0.0 (3)
N1—C8—C9—C10	104.9 (3)	C10—C9—C8—C15	−134.0 (3)
N1—C8—C9—C14	−72.0 (3)	C10—C9—C14—C13	0.0 (3)
C1—C2—C3—C4	0.0 (4)	C10—C11—C12—C13	0.0 (4)
C1—C6—C5—C4	0.0 (4)	C11—C10—C9—C14	0.0 (3)
C2—C1—C6—C5	0.0 (4)	C11—C12—C13—C14	0.0 (4)
C2—C1—C6—C7	−177.1 (3)	C14—C9—C8—C15	49.2 (3)
C2—C3—C4—C5	0.0 (4)	C14—C9—C8—C15	49.2 (3)

Hydrogen-bond geometry (º)

D—H···A	D—H···A
O1—H13···N1	148