Molecular structure of (Z)-6-[(5-chloro-2-hydroxyphenylamino) methylene]-3-(diethylamino)cyclohexa-2,4-dienone: A combined experimental and theoretical study

The crystal structure and spectroscopic properties of ortho-hydroxy Schiff base compound (Z)-6-[(5-chloro-2-hydroxyphenylamino)methylene]-3-(diethylamino)cyclohexa-2,4-dienone were determined by X-ray diffraction, IR and UV–Vis spectroscopy techniques. Molecules of the compound exist as NH tautomeric form in solid state. The gas phase geometry optimizations of two possible tautomeric forms of the title compound were achieved using DFT calculations at B3LYP/6-31G(d,p) level of theory. In order to describe the potential energy barrier belonging to the intramolecular proton transfer and to observe the effects of transfer on the molecular geometry, a relaxed potential energy surface (PES) scan was performed based on the optimized geometry of the NH tautomeric form by varying the redundant internal coordinate, N–H bond distance. At the same level of theory, the vibrational frequencies were calculated and compared with the experimental frequencies. The electronic absorption spectra of the tautomers were calculated using time-dependent density functional theory (TD-DFT) method started from solution phase optimized geometries and compared with the experimental ones.