Synthesis and mesomorphic properties of symmetric tetradentate Schiff bases based on azo-containing salicylaldimines and their copper(II) complexes

Abstract

Two new tetradentate Schiff bases, in which two identical aromatic bent core mesogenic units containing phenylazo are connected via a 1,2-phenylene spacer, N,N′-di-(5-(4-alkoxyphenyl)azo)-salicylidene-1,2-phenylene diimine (alkoxy = decyloxy, dodecyloxy), and their copper(II) complexes were synthesized and studied for their mesomorphic character. The ligands were prepared by the condensation of 5-((4-alkoxyphenyl)azo)salicylaldehydes with 1,2-phenylene diamine. The ligands and their copper complexes have been characterized by IR, ¹H-NMR, electronic spectra, mass spectroscopy, and elemental analyses. The copper complexes were also studied by magnetic moment and electrical conductance measurements. The liquid crystalline properties of the ligands and the related copper complexes were investigated by differential scanning calorimetry (DSC) and by using a polarizing microscope equipped with a heating and cooling stage. None of the free ligands exhibit liquid crystalline behavior but the copper complexes display an enantiotropic smectic C mesophase.

Keywords:

• Schiff base
• Salicylaldimine dimer
• Copper complexes
• Metallomesogen
• Azo compounds
• Smectic C

Acknowledgments

The authors sincerely appreciate the financial support from the ResearchVice Chancellor of Azarbaijan University of Tarbiat Moallem and the faculty of basic science.