In this paper we describe the electrochemical synthesis and characterization of new neutral manganese, iron, cobalt, nickel, copper, zinc, cadmium and lead complexes with the ligand bis(4-N-methylthiosemicarbazone)-2,6-diacetylpyridine, H₄DAPTsz-Me. X-Ray structures of [Mn(H₂DAPTsz-Me)(EtOH)₂] 1, [Pb(H₂DAPTsz-Me)] 3 and [Zn(H₂DAPTsz-Me)]₂·EtOH·2H₂O 4, were also determined. In these complexes the ligand behaves as bis-deprotonated and SNNNS pentadentate. In the manganese complex the metal is heptacoordinated, in a distorted pentagonal-bipyramidal environment, with the N₃S₂ donor set of the ligand in the pentagonal girdle and two solvent molecules occupying the axial positions. In the lead complex 3 the metal is pentacoordinated, bound exclusively to the five donor atoms of the ligand, as a consequence of the existence of “inert pair effect”. The bishelical zinc complex 4 shows each zinc atom with different coordination geometry, one octahedrally six-coordinate while the other is distorted tetrahedrally four-coordinate.

New manganese(II) and manganese(III) complexes of substituted N,N′-bis(salicylidene)-1,2-diimino-2-methylethane have been prepared and characterized. Elemental analysis, IR and EPR spectroscopies, mass spectrometry, magnetic measurements and the study of their redox properties have confirmed their respective formulae as Mn^IIL(H₂O)₂ and Mn^IIIL(H₂O)_n(ClO₄). Electron-withdrawing substituents on the phenyl rings of the ligand stabilize the oxidation state (II) for manganese, but the electron-donating substituents on the Schiff bases are those that lead to Mn(III) complexes, which behave as efficient peroxidase mimics in the presence of the water-soluble trap ABTS. The rate of peroxidase activity of the present complexes is significantly higher than that of other series of Mn-Schiff base compounds, probably due to their versatility in adopting in solution a structure that allows the coordination of the hydrogen peroxide substrate molecule to the manganese.

The neutral dinuclear dihelicate [Cu₂(L)₂]·2CH₃CN (1) forms a unique 3D network in the solid state due to π-stacking interactions, which are responsible for intermolecular antiferromagnetic coupling between Cu(II) ions.

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, Λ_M, 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.