Coordinative trends of a tridentate thiosemicarbazone ligand: synthesis, characterization, luminescence studies and desulfurization processes

Abstract

The coordinative chemistry of the tridentate thiosemicarbazone ligand 2-pyridinecarboxaldehyde 4-N-ethylthiosemicarbazone (HL^Et) has been explored by using an electrochemical methodology. All the complexes have been characterized using analytical and spectroscopic techniques. In the case of copper we have isolated two different complexes, with Cu(L^Et)₂·4H₂O (6) and [Cu₂(L^Et)₂(SO₄)] (7) formulae. The sulfate group coordinated to the copper atoms in 7 was probably released to the media as a consequence of a desulfurization process. Single X-ray crystallography has been carried out for the ligand HL^Et and the complexes 7, [Ag₆(L^Et)₆]·CH₃CN (9) and [Pb(L^Et)₂] (12). The copper(II) complex 7 is a dimer compound in which two antiparallel monodeprotonated ligands are coordinated to two copper centres by establishment of μ₂-thiolate bridges and the additional coordination of a sulfate group bridging the two metal atoms. The silver complex 9 is an unusual hexanuclear cluster compound with a wheel-type conformation, while the lead complex 12 is a monomer which exhibits the lone pair effect. A structural comparative study of the electrochemically obtained complexes derived from HL^X ligands (X= Me, Et and Ph) have been performed. Finally, the solution behaviour of the complexes was checked by NMR, UV and fluorescence studies.