2-Pyridine Carboxaldehyde Hydrazone Ligand and its Complexes: Synthesis and Electrochemical Characterizations

In this work from the reaction of 2- pyridine carboxaldehyde hydrazine ligand (HL) with Nickel (II), Cobalt (II), Manganese (II) and Vanadate ions new complexes was formed as Ni(C13H11N3O2)2, C26H22O4N6Co2Cl2, C13H9O2N3MnCl2, C13H10N3O4V, respectively. These complexes are characterized and identified with x-ray diffraction, elemental analysis and spectroscopic methods. Theses complexes generally crystallize in monoclinic and triclinic systems and space groups of P21/c and P-1[1]. The electrochemical responses of the ligand HL and its complexes were studied by recording the cyclic voltammograms (CV) in the potential range of +1.0 V to -1.0 V[2]. The CV of ligand and its complexes show that all of them are electro-active. HL ligand shows one anodic (Ea=0.31V) and one cathodic (Eb=-0.52V) couple. In CV grams of Co(II) and Ni(II) complexes oxidation peaks are observed in EA1 = 0.59V and EA1 = 0.69V, respectively, displaying some shifts compared to the ligand. In low potentials regarding to the reduction of oxidized Co(II) and Ni(II) complexes, there are one peak in EB = -0.92V for cobalt complex) and EB = -0.64V for Nickel complex. These oxidation/reduction couples could be related to CoIII/CoII and NiII/Ni0 species, respectively. Similarly, for Mn(II) and Vanadate complexes, there are two anodic peaks in EA1 = -0.98V and EA2=0.59V for Mn(II) complexand EA3 = 0.22V and EA4=0.55V for Vanadate complex. In low range potentials, there are two reduction peaks in EB1 = -0.64 V and EB2 = -0.88V for Mn(II) complex and two reduction peaks in EB3 = -0.85 V and EB4 = -0.35V for Vanadet. These reduction peaks could be related to reduction of MnVI to MnIII and MnIII to MnII, VV to VIV and VIV to VIII, respectively [4].