Synthesis and Characterization of Some Unsymmetrical Schiff Bases and Their Copper ( II ) and Nickel ( II ) Complexes

Abstract

The >C=N-unit is an important functional group in organic and bioorganic chemistry. In this study, the possibility of synthesizing unsymmetrical azo-methine Schiff bases was investigated. Successful isolation of tetra-dentate Schiff bases has been accomplished using phenylenediamine derivatives in conjunction with 1-hydroxy-2-acetonaphthone, and salicylaldehyde or 2-hydroxynaphthaldehyde. Nickel(II) and copper(II) salts were found to react with these compounds to produce neutral complexes of the general formula [ML]. On the other hand, it was necessary to employ the template method to complete the reaction between the monocondensate (derived from 1-hydroxy-2-acetonaphthone and phenylenediamine derivative) with 2-pyridinecarbaldehyde (PyL), 2-pyrrolecarbaldehyde (PL), and 2-quinolinecarbaldehyde (QL). The isolated compounds were characterized by means of NMR, IR, elemental analysis, MS, UV-Vis, magnetic susceptibility, and melting point measurement techniques. Theoretical calculations using the DFT/B3LYP theory illustrate that despite the extended conjugation, the isolated complexes are not planar, which is attributed to two main sources of steric hindrance. In addition to their importance as pigments, preliminary biological activity evaluation indicates that some of the complexes may be examined further as potential anti-tumor agents.