Synthesis, 2D NMR and X-ray diffraction studies on Cu(II) and Ni(II) complexes with ligands derived from azobenzene-cored Schiff base: Mesomorphic behaviors of Cu(II)–phenolates and crystal structure of bis[4-(4-alkoxy-2-hydroxybenzylideneamino)azobenzene

Two new homologous series of copper(II) and nickel(II) complexes derived from bidentate Schiff bases 4-(4-alkoxy-2-hydroxybenzylideneamino)azobenzene have successfully been synthesized. Their molecular structures were elucidated by FT-IR, 1H and 13C NMR along with 1H–1H COSY, 1H–13C HMQC, 1H and 13C HMBC. Mesomorphic behaviors of ligands and metal complexes have been investigated by differential scanning calorimetry and polarizing optical microscope. All ligands and their copper complexes exhibit exclusively the mesomorphic properties. The X-ray diffraction studies have confirmed the presence of smectic A (SmA) phase in copper(II)–phenolate complexes. The molecular structure of bis[4-(4-alkoxy-2-hydroxybenzylideneamino)azobenzene]copper(II) have been determined by using X-ray crystallographic techniques. It was found that the ligands have square planar configuration around the Cu center ion as evident by the NCuN and OCuO angles of 180°.

► Copper(II) and nickel(II) complexes derived from bidentate Schiff bases 4-(4-alkoxy-2-hydroxy benzylideneamino)azobenzene.
► All ligands and their copper complexes exhibit mesomorphic properties.
► X-ray diffraction studies confirmed smectic A phase in copper(II)-phenolate complexes.
► Ligands have square planar configuration around the Cu center.