Polymorphs of Thiazole-Derived Imines Connected to Hydroxyaromatics

Conformational polymorphs arising from C–N bond rotation of a methylthiazole ring anchored to a nitrogen atom, which is a constituent of a six-membered intramolecularly hydrogen-bonded system, are studied. We have observed two polymorphs each from 2-(E)-[(5-methylthiazol-2-ylimino)methyl]phenol (1) and 1-(E)-[(5-methylthiazol-2-ylimino)methyl]unaphthalen-2-ol (2). Individual polymorphs are distinguished on the basis of their packing patterns and orientations of functional groups. One polymorph of compound 2, namely polymorph 2b, having Z′ = 2, is metastable; this polymorph is generated on heating of polymorph 2a, which has Z′ = 1.