Liquid-crystalline azines formed by the rare-earth promoted decomposition of hydrazide “habbe” ligands: structural and thermal properties

Abstract

In an attempt to synthesise liquid-crystalline rare-earth complexes of some habbe-type ligands (habbe = N-(2-{(2E)-2-[2-hydroxy-4-(alkoxy)benzylidene]hydrazino}-2-oxoethyl)benzamide), decomposition of these ligands was observed. A synthetic pathway is proposed, in which the rare-earth ion promotes the decomposition of the habbe ligand into a symmetrical azine, which shows mesomorphism. The thermal behaviour of four azines obtained in this way was studied by hot-stage polarizing optical microscopy, differential scanning calorimetry (DSC) and high-temperature powder diffraction methods and shows that all four compounds are liquid-crystalline. The crystal structure of one of the azines has been determined by single crystal X-ray diffraction and shows an elongated orientation of the molecules and a layered crystal packing. Both starting and end products were further characterized by ¹H-NMR.