Thiosemicarbazone ligands are usually [N,S] donors rendering diverse coordination compounds and as [C,N,S] donors they give organometallic complexes. In this work, an unexpected isomerization of a C=N bond in a thiosemicarbazone is described.

The ligands used in this work have been synthesized by condensation reactions and the final product shows an E configured double bond as expected. However, after reaction with palladium salts, the structure of these ligands changes, to give complexes with a C=N Z configuration. This observation has been confirmed by X−ray diffraction studies.

It is not easy to change a double bond from E configuration to Z, therefore this achievement could open a door to investigate new synthetic pathways for isomerizing the C=N double bond in thiosemicarbazones and in related ligands.