Mononuclear and binuclear complexes of salicylidene Schiff bases: synthesis and mesogenic properties

Abstract

The synthesis of new mononuclear and binuclear copper complexes derived from Schiff bases, namely N(4-n-alkyloxysalicylidene)-4′-n-alkylanilines is carried out and their structure and liquid crystalline properties have been investigated. The ligands exhibit rich polymesomorphism; mononuclear complexes exhibit smectic A, smectic C and smectic E phases, while the binuclear complexes mostly exhibit viscous smectic A phase. The isotropic–liquid crystalline transition temperatures of the binuclear complexes in general are found to be lower than their corresponding mononuclear homologues. It was found that the mononuclear complexes exhibit sharp liquid crystalline–isotropic transition temperatures while the binuclear complexes melts over a temperature range. The liquid crystalline phases were characterised by differential scanning calorimetry (DSC) analysis and optical polarised microscopy. X-ray diffraction studies revealed that the intermolecular distance in binuclear complexes is larger than in the mononuclear complexes.

Keywords:

• liquid crystals
• mononuclear and binuclear copper complexes
• synthesis
• enthalpy
• entropy
• optical properties
• X-ray diffraction

Acknowledgements

Financial assistance provided by DST, DRDO, DAE, and UGC, India is gratefully acknowledged. We thank Professor N.A. Clark and Dr C. Jones for their help in providing the experimental facility to obtain X-ray data.