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, H-1 and C-13 NMR (APT and DEPT) and atomic absorption spectroscopy, elemental analyses, thermogravimetric analysis, conductivity and magnetic measurements. In DMSO-d(6) 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.