Our interest in Environmental Chemistry has prompted us to design new materials containing polyfunctional units able to bind certain metallic ions. These materials can be used as modifying agents to produce chemically modified electrodes. We expect to facilitate the detection of organic pollutants in water by binding these materials to an electrode surface. We report a Ni(II) and Co(II) complexes prepared from the Schiff base macroligand N,N´-bis(2-nitrobenzyl)ethylendiimine (L1) with Ni(II) salt and L1 with Co(II) salt. The nature of the complex was established by common spectroscopic techniques. A thermal gravimetric analysis of the complex showed that it is thermodynamically stable. Its formation constant was obtained by conductimetric analysis (Kf = 1.25x106). The affinity of L towards Ni(II) and Co(II) was determined by atomic absorption. The electrochemical study of the complex [Ni(II)-L1]SO4 was also performed by the cyclic voltammetry technique. The results showed that, under certain conditions, this complex is capable of polymerizing on the electrode surfaces made of vitreous carbon and indium tin oxide. The chemical modification on the surface was probed by exploring the cyclic voltammograms, which showed oxidation and reduction peaks that are characteristic of the Ni(II)/Ni(III) pair. The sensing capability towards 2,4-dichlorophenol of these modified electrodes is currently under study.
Keywords

Schiff base Ni(II) complex, electrodes, modifiers
Introduction

There has been a considerable effort in recent years towards the preparation of new materials containing polyfunctional units (ligands) able to bind metallic ions. The Schiff base macroligands [1-6] are synthesized from the reaction of dialdehydes and amino compounds. Given that these materials form stable complexes, they provide the opportunity to design new systems selective to specific metallic ions. These materials could be applied in different areas such as electrochemistry, bioinorganic, catalysis, metallic deactivators, separation processes and environmental chemistry among others [7-9].

New Schiff base [2, 4, 10-11] macroligands have been synthesized to study their selectivity towards complexation of different metallic ions. These newly synthesized compounds are also used as precursors for the formation of other acyclic and cyclic ligands.

Complexes of Schiff base ligands with structural similarities to phtalocyanines (N4-macrocycles) [7, 12-14], and other related compounds [15-20], are currently used as modifiers of the active surface of electrodes to improve their catalytic activity in the selective detection of organic pollutants [15, 21-24] and the entrainment of metals. Along the same line, our interest is to evaluate the capability of N,N’-bis(2-nitrobenzyl)ethylendiimine L1 (Figure 1), to bind diverse metallic ions such as Ni(II) and Co(II), and carry out selectivity studies. These complexes are later studied to test their potential in the development of chemically modified electrodes for use in pollutant detection.