3-[(E)-(4-Ethyl­phen­yl)imino­meth­yl]benzene-1,2-diol

Zeynep Keleşoğlu; Orhan Büyükgüngör; Çiğdem Albayrak; Mustafa Odabaşoğlu

doi:10.1107/S1600536809029924

. 2009 Jul 31;65(Pt 8):o2055. doi: 10.1107/S1600536809029924

3-[(E)-(4-Ethylphenyl)iminomethyl]benzene-1,2-diol

Zeynep Keleşoğlu ^a,^*, Orhan Büyükgüngör ^a, Çiğdem Albayrak ^b, Mustafa Odabaşoğlu ^c

PMCID: PMC2977215 PMID: 21583717

Abstract

The title compound, C₁₅H₁₅NO₂, adopts the enol–imine tautomeric form. The dihedral angle between the two benzene rings is 48.1 (1)°. Intramolecular O—H⋯N and O—H⋯O hydrogen bonds generate S(6) and S(5) ring motifs, respectively. In the crystal, molecules are linked into centrosymmetric R ₂ ²(10) dimers via pairs of O—H⋯O hydrogen bonds and the dimers may interact through very weak by π–π interactions [centroid–centroid distance = 4.150 (1) Å]. The ethyl group is disordered over two orientations, with occupancies of 0.587 (11) and 0.413 (11).

Related literature

For the photochromic and thermochromic properties of Schiff base compounds, see: Elmali et al. (1999 ▶); Guha et al. (2000 ▶); Kletski et al. (1997 ▶); Kownacki et al. (1994 ▶); Zgierski et al. (2000 ▶). For Schiff base tautomerism, see: Alarcon et al. (1995 ▶); Dudek et al., (1966 ▶); Salman et al. (1991 ▶, 1993 ▶). For a related structure, see: Özek et al. (2009 ▶). For graph-set motifs, see: Bernstein et al. (1995 ▶).

Experimental

Crystal data

C₁₅H₁₅NO₂
M _r = 241.28
Triclinic,
a = 6.1893 (4) Å
b = 8.7704 (6) Å
c = 12.7605 (9) Å
α = 87.326 (6)°
β = 86.397 (6)°
γ = 69.394 (5)°
V = 646.85 (8) Å³
Z = 2
Mo Kα radiation
μ = 0.08 mm⁻¹
T = 296 K
0.54 × 0.41 × 0.31 mm

Data collection

Stoe IPDS II diffractometer
Absorption correction: integration (X-RED32; Stoe & Cie, 2002 ▶) T _min = 0.966, T _max = 0.979
8683 measured reflections
2668 independent reflections
1896 reflections with I > 2σ(I)
R _int = 0.042

Refinement

R[F ² > 2σ(F ²)] = 0.051
wR(F ²) = 0.148
S = 1.03
2668 reflections
191 parameters
28 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.24 e Å⁻³
Δρ_min = −0.13 e Å⁻³

Data collection: X-AREA (Stoe & Cie, 2002 ▶); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536809029924/ci2862sup1.cif

e-65-o2055-sup1.cif^{(18.8KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809029924/ci2862Isup2.hkl

e-65-o2055-Isup2.hkl^{(128.3KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯N1	0.95 (3)	1.72 (3)	2.596 (2)	152 (2)
O2—H2⋯O1	0.88 (3)	2.29 (3)	2.7307 (19)	111 (2)
O2—H2⋯O1ⁱ	0.88 (3)	2.06 (3)	2.818 (2)	143 (2)

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Symmetry code: (i) Inline graphic .

Acknowledgments

The authors acknowledge the Faculty of Arts and Sciences, Ondokuz Mayıs University, Turkey, for the use of the Stoe IPDS II diffractometer (purchased under grant F.279 of the University Research Fund).

supplementary crystallographic information

Comment

There has been considerable interest in some Schiff bases derived from salicylaldehyde and substituted salicylaldehyde because they show thermochromism and photochromism in the solid state (Kownacki et al., 1994). The tautomerism in the Schiff base ligands plays an important role for distinguishing their photochromic (Guha et al., 2000) and thermochromic (Zgierski et al., 2000) characteristics. It has been proposed that molecules showing thermochromism are planar, while those showing photochromism are non-planar (Kletski et al., 1997), both phenomena being associated with a proton transfer (Elmali et al., 1999). Schiff bases derived from the condensation of salicylaldehyde with aniline and substituted aniline, and naphthaldehyde with aniline exists as enol-imine (Dudek et al., 1966), keto-amine (Salman et al., 1991), or enol-imine/keto-amine form (Salman et al., 1993; Alarcon et al., 1995) in all solvents.

The X-ray analysis shows that the title compound prefers an enol-imine tautomeric form, with a strong intramolecular O1—H1···N1 hydrogen bond. This is also confirmed by the C2—O1 [1.361 (2) Å], C7—N1 [1.278 (2) Å], C1—C7 [1.445 (2) Å] and C1—C2 [1.399 (2) Å] bond lengths (Fig. 1). The C2—O1 bond length of 1.361 (2) Å indicates a single-bond character and the C7—N1 bond length of 1.278 (2) Å indicates a high degree of double-bond character. Similar results were observed for (E)-4-methoxy-2-[(o-tolilimino)methyl]phenol [C—O = 1.357 (2) Å, C═N= 1.286 (2) Å; Özek et al., 2009]. An intramolecular O2—H2···O1 hydrogen bond is also observed. The O—H···N and O—H···O hydrogen bonds generate S(6) and S(5) ring motifs, respectively (Bernstein et al., 1995).

The dihedral angle between benzene rings A(C1-C6) and B(C8-C13) is 48.1 (1)°. The nearly planar S(6) ring C(O1/H1/N1/C1/C2/C7) is oriented with respect to rings A and B at dihedral angles of A/C = 1.89 (42)° and B/C = 46.23 (25)°. It is known that Schiff bases may exhibit thermochromism or photochromism, depending on the planarity or non-planarity of the molecule, respectively. Since the title moleclule is non-planar, one can expect photochromic properties in title compound.

In the crystal structure, molecules are linked into centrosymmetric R₂²(10) dimers via O—H···O hydrogen bonds (Table 2). A very weak π–π interaction occurs between A(C1-C6) rings at (x, y, z) and (1-x, 1-y, 1-z), with a ring centroid-to centroid distance of 4.150 (1) Å; only atoms C1, C2 and C3 are involved in the interactions as the rings are displaced.

Experimental

Compound (I) was prepared by refluxing a mixture of 2,3-dihidroxy benzalaldehyde (0.5 g 0.0036 mol) in ethanol (20 ml) and 4-ethylaniline (0.436 g 0.0036 mol) in ethanol (20 ml). The reaction mixture was stirred for 1 h under reflux. Single crystals of (I) suitable for X-ray analysis were obtained by slow evaporation of a methanol solution (yield 87%, m.p. 378-379 K).