An orthorhombic polymorph of 5-[(4-methylphenyl)diazenyl]salicylaldehyde

The title compound, C14H12N2O2, is an orthorhombic polymorph of the previously reported monoclinic form [Bakir et al. (2005 ▶). Acta Cryst. E61, o1611–o1613]. The dihedral angle between the aromatic rings is 4.32 (13)°. The molecular structures of the two polymorphs, including short intramolecular O—H⋯O hydrogen bonds between the the hydroxy and keto groups, are quite similar but their crystal packings are distinct. Unlike the monoclinic form, in which centrosymmetrically related hydroxy and keto groups form {⋯H⋯O}2 synthons via weak O—H⋯O contacts, leading to dimeric aggregates, in the orthorhombic form, the hydrogen bonding between these groups leads to the formation of supramolecular chains orientated along the a axis.

The title compound, C 14 H 12 N 2 O 2 , is an orthorhombic polymorph of the previously reported monoclinic form [Bakir et al. (2005). Acta Cryst. E61, o1611-o1613]. The dihedral angle between the aromatic rings is 4.32 (13) . The molecular structures of the two polymorphs, including short intramolecular O-HÁ Á ÁO hydrogen bonds between the the hydroxy and keto groups, are quite similar but their crystal packings are distinct. Unlike the monoclinic form, in which centrosymmetrically related hydroxy and keto groups form {Á Á ÁHÁ Á ÁO} 2 synthons via weak O-HÁ Á ÁO contacts, leading to dimeric aggregates, in the orthorhombic form, the hydrogen bonding between these groups leads to the formation of supramolecular chains orientated along the a axis.

Comment
The title compound, (I), was isolated during on-going studies into the biological activities of their organotin complexes (Basu Baul et al., 2005). The structure of (I) represents an orthorhombic polymorph of a previously reported monoclinic form (Bakir et al., 2005). The molecular structure of (I), Fig. 1, closely resembles that of the monoclinic form, with comparable geometric parameters being equal within experimental error. The overall molecule of (I) is planar as seen in the values of the C1/C2/C3/O2, C5/C4/N1/N2 and C9/C8/N2/N1 torsion angles of 0.9 (4), 0.7 (4) and -178.0 (2) °, respectively. In each of the polymorphs, a short intramolecular O-H···O hydrogen bond is formed between the hydroxyl and keto groups, Table 1. The key difference between the polymorphs rests with the nature of the weaker O-H···O intermolecular interactions formed between these groups. Thus, in the previously reported monoclinic form, the crystal structure comprises the packing of centrosymmetric dimers linked by a four-membered {···H···O} 2 synthon. By contrast, in (I) the intermolecular hydrogen bonding between these groups leads to 1-D supramolecular chains aligned along the a direction, Table 1 and Fig. 2. The crystal structure comprises packing of these chains as illustrated in Fig. 3.

Experimental
Compound (I) was prepared by reacting p-tolyldiazonium chloride with o-hydroxybenzaldehyde using a previously reported method (Sarma et al., 1993). Orange crystals were obtained by slow evaporation of a methanol solution of (I); m.pt. 421-423 K.

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.95-0.98 Å) and were included in the refinement in the riding model approximation with U iso (H) set to 1.2-1.5U eq (C). The O-bound H-atom was located in a difference Fourier map and was refined with an O-H restraint of 0.840±0.001 Å, and with U iso (H) = 1.5U eq (O).

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes.
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 > 2σ(F 2 ) is used only for calculating Rfactors(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.