engleski

Multinuclear NMR and X-ray Diffraction Analysis of Some Thiosemicarbazone Derivatives

Thiosemicarbazones and their corresponding metal complexes are widely known compounds possessing diverse pharmacological activities, such as antitumor, antivirial, antibacterial, antifungal, antimalarial, etc. Bioactivity is closely related to molecular conformation which can significantly be affected by the presence of intra- and inter-molecular hydrogen bonds. Salicylaldehyde thiosemicarbazones can exist in several tautomeric forms with both intra- and inter-molecular hydrogen bonds. An intra-molecular O―H•••N H-bond between the hydroxyl group and the azomethine N atom has been found in salicylaldehyde thiosemicarbazone family (resonance assisted H-bond). Additionally, an intramolecular N―H •••N H-bond between the thiourea NH group and the azomethine N atom was found in few salicylaldehyde thiosemicarbazones. The aim of this research is to investigate the influence of substituents and solvents (different polarities, i. e. of different proton donor and acceptor abilities) on molecular conformation, tautomerism and structure of H-bonds in salicylaldehyde thiosemicarbazone derivatives. We present here a part of our study regarding the effect of substituting OH with OMe group in salycilaldehyde residue (therefore, breaking the O―H•••N H-bond) on the overall structure and thione-thiol tautomerism. Solid state structures of two thiosemicarbazone derivatives 1 and 2 (two polymorphs) were characterized by high resolution 15N and 13C solid-state NMR spectroscopy and X-ray diffraction. The results were compared with those obtained for CDCl3 and DMSO solutions. Possible tautomeric equilibrium changes were probed by multinuclear temperature dependent NMR experiments.

NMR; X-ray; thiosemicarbazones; solid state; solution

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