(E)-4-Bromo-2-[(phenylimino)methyl]phenol: a new polymorph and thermochromism.

A new polymorph of (E)-4-bromo-2-[(phenylimino)methyl]phenol, CHBrNO, is reported, together with a low-temperature structure determination of the previously published polymorph. Both polymorphs were found to have an intramolecular O-H...N hydrogen bond between the phenol OH group and the imine N atom, forming an S(6) ring. The crystals were observed to have different colours at room temperature, with the previously published polymorph being more orange and the new polymorph more yellow. The planarity of the molecule in the two polymorphs was found to be significantly different, with dihedral angles (Φ) between the two aromatic rings for the previously published orange' polymorph of Φ = 1.8 (2)° at 120 K, while the new yellow' polymorph had Φ = 45.6 (1)° at 150 K. It was also observed that both polymorphs displayed some degree of thermochromism and upon cooling the orange' polymorph became more yellow, while the yellow' polymorph became paler upon cooling.