Hexacatenar liquid-crystalline complexes of palladium(II) and platinum(II) based on trialkoxystilbazole esters

The synthesis and characterisation of 4-(3,4,5-trialkoxybenzoyloxy)pyridines (<b>1a–e</b>), and of their corresponding palladium(II), (<b>2a–e</b>), and platinum(II), (<b>3a–e</b>), complexes are described. The pyridine-based ligands are not mesomorphic, but upon complexation to PdCl₂ or PtCl₂, new hexacatenar mesogens are formed which show exclusively the hexagonal columnar mesophase. The mesomorphic behaviour of the complexes was characterised by polarised optical microscopy, differential scanning calorimetry and X-ray diffraction. The metal seems to influence the crystal phase and mesophase stability as well as the mesomorphic temperature range.