Liquid crystalline behaviour of Nickel(II) complexes derived from alkoxybenzoylhydrazide: synthesis, characterisation, and mesophase study

The Nickel(II) complexes of {N’-4(4’-alkoxybenzoyloxy)benzylidene}-3-(decyloxy)benzoylhydrazide was synthesised and characterised to investigate its structural and mesomorphic properties. The structure was confirmed by FT-IR, Elemental, 1H-NMR, 13C-NMR, and 1H-1H COSY spectroscopy, which indicated successful coordination through the azomethine nitrogen and carbonyl oxygen atoms. To explore the impact of alkoxy chain length on mesomorphism, additional homologous compounds bearing longer alkyl chains (C8-C18) were also studied for their phase behaviour. Mesophase investigations were performed using polarising optical microscopy (POM) and differential scanning calorimetry (DSC). All complexes exhibited nematic liquid crystalline phases. The phase transition temperatures were found to vary systematically with increasing chain length, reflecting enhanced flexibility and packing behaviour within the molecular structures. DSC analysis supported microscopic observations, showing distinct endothermic and exothermic transitions corresponding to crystal-LC-isotropic and reverse transformations. The texture observed under POM confirmed the formation of nematic phases characterised by high mobility and birefringence. These findings underscore the critical role of molecular design, particularly terminal chain length, in tuning the liquid crystalline behaviour of metal-hydrazone complexes.