Larisa Malykhina

Synthesis, Mesomorphism, and Unusual Magnetic Behaviour of Lanthanide Complexes with Perfluorinated Counterions

Lanthanide complexes of the Schiff base ligand 4-dodecyloxy-N-hexadecyl-2-hydroxybenzaldimine and with perfluorinated alkyl sulfate counterions were synthesised. All of the metal complexes show a smectic A mesophase. The viscosity of this mesophase is much lower than that of analogous compounds with nitrate or alkyl sulfate counterions. The behaviour of these new highly anisotropic molecular magnetic materials was studied using high-temperature X-ray measurements in an external magnetic field and temperature-dependent magnetic susceptibility measurements. The mu(eff)-versus-temperature curve is more comparable with those expected for nematic phases than for smectic phases. The luminescence spectrum of a EuIII compound shows that the values of the second rank crystal field parameters are very large. The huge magnetic anisotropy can be related to this strong crystal-field perturbation.

Anisotropic molecular magnetic materials based on liquid-crystalline lanthanide complexes

Abstract 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.

Luminescent lanthanide complexes with liquid crystalline properties

Lewis-base adducts of tris(β -diketonato)lanthanide(III) complexes were prepared, where the β -diketone is para -alkoxy-substituted 1,3-diphenyl-1,3-propanedione. These compounds are the first examples of liquid crystalline lanthanide complexes in which the mesomorphism is introduced via a β -diketonate ligand. Depending on the type of the Lewis base, the metallomesogens exhibit a monotropic smectic A or a monotropic highly ordered smectic phase. Intense photoluminescence was observed for the europium(III) complexes at room temperature.

Formation of lanthanide ion networks by orientation of the mesophases of their complexes in magnetic fields

A complex of a Tm(III) perfluoroalkylsulsphate with salicylaldimine Schiffs base was synthesized and its liquid crystallinity characterized by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. An additional phase transition was detected. 2D or 3D anisotropically-organized media were obtained by cooling of the lanthanide complex from different phases in an applied magnetic field. A huge positive magnetic anisotropy was observed for the resulting material.