Mesomorphism of lanthanide-containing Schiff's base complexes with chloride counterions

Liquid crystalline complexes [Ln(LH)(3)Cl-3] have been synthesized, where Ln is a trivalent lanthanide ion (Pr-Lu, except Pm) and where LH is the Schiff's base ligand N-octadecyl-4-tetradecyloxysalicylaldimine. Although the ligand does not exhibit mesomorphism, the complexes do (SmA phase). The mesophase behaviour of these compounds has been investigated by polarizing optical microscopy, differential scanning calorimetry and high temperature X-ray diffraction. The lanthanide complexes have much higher melting and clearing points than comparable complexes with nitrate or dodecyl sulphate counterions. In addition, the transition temperatures are virtually independent of the type of lanthanide ion. This behaviour is opposite to that observed for similar complexes with nitrate counterions [Ln(LH)(3)(NO3)(3)]. The differences in temperature dependence can be related to structural differences. Whereas in the nitrate complexes the Schiff's base ligand binds in a zwitterionic form, two-dimensional H-1 NMR correlation spectroscopy (COSY) of [Lu(LH)(3)Cl-3] gives an indication that in the chloride complexes, besides coordination via the oxygen of molecules in the zwitterionic form, some of the Schiff's base ligands bind in a bidentate fashion (via the phenolic oxygen and the imine nitrogen)

Adducts of Schiff bases with tris(beta-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