The synthesis and structures of three isoxazole-containing Schiff bases are reported, namely, (E)-2-{[(isoxazol-3-yl)imino]methyl}phenol, C10H8N2O2, (E)-2-{[(5-methylisoxazol-3-yl)imino]methyl}phenol, C11H10N2O2, and (E)-2,4-di-tert-butyl-6-{[(isoxazol-3-yl)imino]methyl}phenol, C18H24N2O2. All three structures contain an intramolecular O-H...N hydrogen bond, alongside weaker intermolecular C-H...N and C-H...O contacts. The C-O(H) and imine C=N bond lengths were consistent with structures existing in the enol rather than the keto form. Despite having dihedral angles <25°, none of the compounds were observed to be strongly thermochromic, unlike their anil counterparts; however, all three compounds showed a visible colour change upon irradiation with UV light.
Keywords: Schiff base; chromism; crystal structure; hydrogen bonding; isoxazole; phenol.
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