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Supramolecular Influence on Keto-Enol Tautomerism and Thermochromic Properties of o- Hydroxy Schiff Bases

This work presents a study on thermo-optical properties of three Schiff bases (imines) in the solid state. The Schiff bases were obtained by means of mechanochemical synthesis using monosubstituted o-hydroxy aromatic aldehydes and monosubstituted aromatic amines. The keto- enol tautomerism and proton transfer via intramolecular O∙∙∙N hydrogen bond of the reported compounds was found to be influenced more by supramolecular interactions than by a temperature change. All products were characterised by powder X-ray diffraction (PXRD), FT-IR spectroscopy, thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Molecular and crystal structures of compounds 1, 2 and 3 were determined by single crystal X-ray diffraction (SCXRD). The molecules of 1 appear to be present as the enol-imine, the molecules of 2 as the keto-amine tautomer and the molecules of 3 exhibit keto-enol tautomeric equilibrium in the solid state. An analysis of Cambridge structural database (CSD) data on similar imines has been used for structural comparison.

keto-enol tautomerism ; Schiff bases ; mechanochemistry ; thermochromism.

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