Adducts of Schiff bases with tris(β-diketonato)lanthanide(III) complexes:: Structure and liquid-crystalline behaviour

Adducts of the Schiff base 2-hydroxy-N-octadecyloxy-4-tetradecyloxybenzaldimine with tris(beta-dibenzoylmethanato)lanthanide(III) complexes are described. The stoichiometry of the complexes is [Ln(dbM)(3)L-x], where Ln is a trivalent lanthanide ion (all lanthanides except Ce and Pm), Hdbm is dibenzoylmethane and L is the Schiff base; x = 2 for Ln = La-Er and x = 1 for Ln = Tm-Lu. The Schiff-base ligands are in a zwitterionic form and coordinate through the phenolic oxygen only. The X-ray single-crystal structure of [La(dbm)(3)L'(2)] with L' = N-butyl-2-hydroxy-4-methoxybenzaldimine is described. The solution structure of lanthanum(III) complexes has been investigated by 1D and 2D H-1 NMR techniques. Although the long-chain Schiff-base ligand and the tris(beta-dibenzoylmethanato)lanthanide(III) complexes are non-mesomorphic, some of the adducts exhibit a monotropic smectic A phase. The mesomorphic behaviour depends on the lanthanide ion, in the sense that only a mesophase is observed for the series Ln = La-Eu, not for the heavier lanthanides. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.