Zn(II) pyrazolonate complexes obtained by metal-induced cyclization of thiosemicarbazones: Crystal structures and spectroscopic properties

The reaction of zinc(II) acetate with thiosemicarbazones derived from β-keto esters (methyl propionylacetate thiosemicarbazone, ethyl benzoylacetate thiosemicarbazone, ethyl 2-ethylacetoacetate thiosemicarbazone and methyl acetoacetate ¹N-ethylthiosemicarbazone) induces the cyclization of the thiosemicarbazone to afford ZnL₂] and (in one case) ZnL₂(MeOH)] complexes, where HL is a substituted 2,5-dihydro-5-oxo-1H-pyrazolone-1-carbothioamide. The four complexes were studied by X-ray diffraction, which showed that the pyrazolonate ligand binds with the metal through the S and N(3) atoms. The influence of cyclization and metallation on the ¹H and ¹³C NMR spectra of the starting thiosemicarbazones is also discussed.