Synthesis, characterisation and mesomorphic properties of ester containing aroylhydrazones and their nickel(II) complexes

Abstract

A new series of mesogenic aroylhydrazone-based ligands, N-[4-(4′-alkoxy)benzoyloxybenzylidene]-N′-[4″-alkoxybenzoyl]hydrazine with either the same or different peripheral alkyl chains, and nickel(II) complexes of some of them have been synthesised. They were characterised by elemental analyses, Fourier transform infrared, proton and carbon nuclear magnetic resonance and ultraviolet-visible spectroscopy. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry and polarising optical microscopy. All the aroylhydrazones, except those with no lateral chains on either end of the molecule and where m = n = 14, 16, exhibit a monotropic or enantiotropic smectic C mesophase, which are almost insensitive to the peripheral alkoxy chain length. The square planar nickel(II) complexes of the ligands show only an isotropic phase at higher temperature (>175°C) and no mesogenic nature is observed. Density functional theory calculations have been performed using the GAUSSIAN-03 program at the Becke, three-parameter, Lee–Yang–Parr level to obtain the stable electronic structure of the ligand.

Keywords:

• aroylhydrazone
• enantiotropic mesophase
• differential scanning calorimetry
• polarising optical microscopy
• density functional theory

Acknowledgements

One of the authors, SKS, thanks Banaras Hindu University, Varanasi, India for financial support through a research scholarship. The authors thank Dr Ranjan K. Singh, Department of Physics, Banaras Hindu University, Varanasi, India for the computational facility. Thanks are also due to the reviewer for his valuable comments.