Conformational rearrangement of 2,6-bis(1-salicyloylhydrazonoethyl)pyridine (H₄daps) on complexation. Synthesis and X-ray characterisation of H₄daps and its copper helicate complex [Cu(H₂daps)(H₂O)]₂·2CH₃CN

Abstract

The copper complex of 2,6-bis(1-salicyloylhydrazonoethyl)pyridine, H4daps, has been prepared by an electrochemical procedure and characterised by elemental analysis, IR, FAB mass spectroscopy, ΛM, magnetic susceptibility measurements and EPR studies. The molecular structures of the ligand H4daps (1) and its copper complex [Cu(H2daps)(H2O)]2·2CH3CN (3) have been determined by X-ray diffraction studies. The ligand shows in the solid state a syn-open conformation that allows it to act as a binucleating ligand, after a conformational change, as is shown by the study of the copper dihelicate 3. This compound contains the dianionic ligand [H2daps]2− in an anti-open conformation. The comparative study of this complex, with others previously reported, allows us to confirm that the conformational rearrangement undergone by H4daps upon complexation depends strongly on the metal nature and its stereochemical preferences.