Synthesis and Characterization of Copper(II), Nickel(II) and Cobalt(II) Complexes with Azo‐Linked Schiff Base Ligands

Diazo compounds were prepared by coupling of benzenediazonium chloride ions with 4‐amino‐5‐hydroxy‐2,7‐naphthalenedisulfonic acid mono sodium salt under alkaline conditions, and new Schiff bases H2L and H2L1 were then obtained by the condensation of 4‐amino‐5‐hydroxy‐6‐(2,5‐dicholorophenylazo)‐2,7‐naphthalene disulfonic acid disodium salt and 4‐amino‐5‐hydroxy‐6‐(2‐nitrophenylazo)‐2,7‐naphthalenedisulfonic acid disodium salt with o‐vanillin. New Cu(II), Ni(II) and Co(II) complexes of the Schiff base ligands were also prepared and characterized by IR, UV‐Vis, 1H and 13C NMR (APT and DEPT) and atomic absorption spectroscopy, elemental analyses, thermogravimetric analysis, conductivity and magnetic measurements. In DMSO‐d6 solutions, it was found that the azo‐linked Schiff base ligands are in equilibrium with their corresponding and strongly prevailing hydrazone tautomers. The results suggested that the condensation of the azo‐derivative compounds and o‐vanillin in 1:1 molar ratio produces mononuclear Schiff base ligands with an ONO donor set.