Synthesis and Magnetic Investigations on Rare-Earth-Containing Liquid Crystals with Large Magnetic Anisotropy

A new series of liquid-crystalline Schiff base lanthanide compounds of the general formula (L‘‘H)2L‘‘MX2 was prepared (L‘‘H = H2n+1CnOC6H3(OH)CHNCmH2m+1; n = 7, 12; m = 14, 18; M = La, Tb, Dy, Er, Nd, Ho, Eu, Pr, and Gd; X = NO3 or Cl). The thermal behavior of these complexes was examined by polarizing microscopy, differential scanning calorimetry, and X-ray diffraction experiments. The ligands L‘‘H are nonmesomorphic, but all lanthanide complexes show smectic A mesophases. Further, temperature-dependent magnetic susceptibility measurements were carried out in order to obtain information about the magnetic anisotropy of the lanthanide compounds. The Tb(III) and Dy(III) derivatives could be oriented by a magnetic field. These liquid-crystalline lanthanide complexes display magnetic anisotropies which are two orders of magnitude greater than those of known liquid crystals.