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.