Mesogenic Properties of Binucleating Schiff-Base Ligands with Long Side Chains and Their Binuclear Cu(II) and Ni(II) Complexes

ABSTRACT

Liquid-crystalline binucleating ligands, 1,4-[bis(2-hydroxy-4-(n-alkoxy)benzaldimino]benzene, and their binuclear nickel and copper complexes have been synthesized, with the aim to study the effect of the long alkoxy chain substituents on the mesogenic properties of the ligand and on the extent of electronic interaction between the two paramagnetic metal centers for binuclear Cu(II) complexes. The ligand and the complexes have been characterized by elemental analyses, IR, ¹H NMR, and FAB mass and electronic spectral studies. Magnetic moment studies of the Cu (II) complexes show that there is antiferromagnetic spin-exchange interaction between the two Cu (II) centers through the phenyl bridge. The variable temperature magnetic studies show that the extent of spin-exchange interaction decreases with the increase in the length of the alkoxy side chain. The ligands 1,4-bis-(2-hydroxy-4-(n-alkoxy)benzaldimino)benzene exhibit liquid-crystalline properties with the smectic C phase. The mesogenic property of the ligand disappears on complex formation.

Keywords:

• binuclear complex
• liquid crystal
• metallomesogen
• spin exchange interaction

Acknowledgments

The authors thank the Head, Department of Chemistry, M. S. University of Baroda for providing the laboratory facility; RSIC, CDRI, Lucknow for the FAB mass spectral studies; RSIC, IIT Bomaby for the ESR spectral studies, and S. Menon of the Gujarat University, Ahmedabad, for allowing us to use the electrochemical assembly. The authors also thank to J. S. Dave and P. Patel of the Applied Chemistry Department, M. S. University of Baroda, for their help in the study of the liquid-crystalline materials.

Notes

^a Calculated values in parentheses.

^b In acetonitrile solution.

^c Extinction coefficient.