Anisotropic molecular magnetic materials based on liquid-crystalline lanthanide complexes

The alignment of liquid crystals in an external magnetic field is discussed. Special attention is paid to paramagnetic metallomesogens containing trivalent lanthanide ions. The huge magnetic anisotropy of rare-earth compounds is favourable to achieve easy magnetic alignment. The principle of orientation of liquid-crystalline lanthanide complexes is illustrated for Schiff base complexes of the type [Ln(LH)3(NO3)3], where Ln is a trivalent lanthanide ion and LH is a salicylaldimine. The compounds exhibit a smectic A phase. By a proper choice of the lanthanide ion, it is possible to align the director either parallel or perpendicular to the magnetic field. When the aligned mesophase is cooled in the presence of a magnetic field, the mesophase order is frozen into the glass state and an anisotropic molecular magnetic material is obtained.