An ortho-rhom-bic polymorph of 5-[(4-methyl-phen-yl)diazen-yl]salicylaldehyde.

The title compound, C(14)H(12)N(2)O(2), is an ortho-rhom-bic 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 mol-ecular structures of the two polymorphs, including short intra-molecular O-H⋯O hydrogen bonds between the the hydr-oxy and keto groups, are quite similar but their crystal packings are distinct. Unlike the monoclinic form, in which centrosymmetrically related hydr-oxy and keto groups form {⋯H⋯O}(2) synthons via weak O-H⋯O contacts, leading to dimeric aggregates, in the ortho-rhom-bic form, the hydrogen bonding between these groups leads to the formation of supra-molecular chains orientated along the a axis.