2-Hydroxy-6-[ ( m-tolyliminio ) methyl ] phenolate

In the solid state, the title compound, C14H13NO2, crystallizes as a zwitterion. Two molecules comprise the asymmetric unit. The molecules exhibit two types of hydrogen bonds: N-H center dot center dot center dot O hydrogen bonds involving hydroxy and imine groups generate an S(6) ring motif, and O-H center dot center dot center dot O hydrogen bonds linking two symmetry-related molecules form a centrosymmetric dimer.

In the solid state, the title compound, C 14 H 13 NO 2 , crystallizes as a zwitterion. Two molecules comprise the asymmetric unit. The molecules exhibit two types of hydrogen bonds: N-HÁ Á ÁO hydrogen bonds involving hydroxy and imine groups generate an S(6) ring motif, and O-HÁ Á ÁO hydrogen bonds linking two symmetry-related molecules form a centrosymmetric dimer.

Comment
Hydroxy Schiff bases have been extensively studied due to their biological, photochromic and thermochromic properties (Garnovskii et al., 1993;Hadjoudis et al., 2004). They can be used as potential materials for optical memory and switch devices (Zhao et al., 2007). Proton transfer in these compounds forms the basis for an explanation of the mechanisms of various biological processes where proton transfer is the rate-determining step (Lussier et al., 1987). The title Schiff base, (I), was obtained by the condensation of 2,3dihydroxybenzaldehyde with 3-methylaniline.
Molecules 1 and 2 exhibit two types of hydrogen bonds, an intramolecular N-HÁ Á ÁO hydrogen bond and two intermolecular O-HÁ Á ÁO hydrogen bonds ( Fig. 3 and Table 1). In the crystal packing of (I), symmetry-related molecules are linked by O-HÁ Á ÁO hydrogen bonds forming centrosymmetric dimers, which stack along the b axis direction.
N-and O-bound H atoms were located in a difference Fourier map and refined with isotropic displacement parameters. All other H atoms were generated by geometrical considerations and were included in the riding-model approximation, with U iso (H) = xU eq (C), where x = 1.5 for methyl and x = 1.2 for the other H atoms. The methyl groups were refined as rigid groups, which were allowed to rotate freely. Assigned values of bond distances: methyl C-H = 0.98 Å and aromatic C-H = 0.95 Å . The N-H bonds are involved in an intramolecular hydrogen bond; the observed N-H bond distances are elongated compared with commonly observed values of around 0.85-0.90 Å .
Data collection: SMART (Bruker, 2006); cell refinement: SAINT-Plus (Bruker, 2006); data reduction: SAINT-Plus; program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics:  The structure of molecule 1 of the asymmetric unit of (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown with an arbitrary radius.

Figure 2
The structure of molecule 2 of the asymmetric unit of (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown with an arbitrary radius.

Data collection
Bruker SMART APEX CCD area-detector diffractometer Radiation source: fine focus sealed Siemens Mo tube Parallel mounted graphite monochromator Detector resolution: 4096x4096 / 62x62 (binned 512) pixels mm -1 φ and ω scans Absorption correction: multi-scan (SADABS; Bruker, 2006) T min = 0.955, T max = 0.989 7014 measured reflections 4253 independent reflections 2951 reflections with I > 2σ(I) where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.28 e Å −3 Δρ min = −0.21 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.