Influence of the ligand structure on the liquid crystalline properties of lanthanide-containing salicylaldimine mesogens

The synthesis and liquid crystalline properties of lanthanide complexes with different but structurally related Schiff's base ligands are described. The complexes all contain nitrate counterions and have the stoichiometry [Ln(LH) 3 (NO 3 ) 3 ], where Ln is a trivalent rare-earth ion (La, Nd, Gd or Ho) and LH is a Schiff's base ligand. None of the Schiff's base ligands exhibits mesomorphism, but some of the complexes do (SmA phase). It is shown that the presence or absence and the position of substituents on the ligand determine whether or not the complexes show mesomorphism. The thermal behaviour of these compounds has been investigated by hot stage polarizing microscopy and differential scanning calorimetry.