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

Abstract

Lanthanide complexes of the Schiff base ligand 4-dodecyloxy-N-hexa-decyl-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 m eff-versus-temperature curve is more comparable with those expected for nematic phases than for smectic phases. The luminescence spectrum of a Eu III 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.

Room-temperature magnetic anisotropy of lanthanide complexes: A model study for various coordination polyhedra

“…Magnetic anisotropies of about 50 000 ϫ10 Ϫ6 cm 3 mol Ϫ1 can be obtained in many coordination polyhedra, which is more than two orders of magnitude larger than that for transition metal complexes or organic compounds. [10][11][12][13][14][15] The upper limit of the room-temperature anisotropy is estimated to be about 80 000 ϫ10 Ϫ6 cm 3 mol Ϫ1 ͓Tb͑III͒ ion in the elongated square anti-prism͔. The magnetic anisotropy of the light lanthanide ions ͑Ce-Eu͒ is considerably lower ͑typically, by one order of magnitude͒ than that of heavy lanthanide ions ͑Tb-Yb͒.…”

“…This property is potentially important for practical uses, such as designing magnetically active liquid crystals. [10][11][12][13][14][15] The magnetic anisotropy of lanthanide ions doped in bilayered micelles or protein molecules is of interest for biological applications. 16 -20 Thus, the magnetic anisotropy of lanthanide ions incorporated in the calcium protein calbindin D 9k was recently studied.…”

“…20 Lanthanide-containing liquid crystals are particularly interesting materials since, in contrast to conventional organic diamagnetic liquid crystals, they can be easily oriented in a rather weak magnetic field. [10][11][12][13][14] The director n of the liquid crystal is oriented either parallel or perpendicular to the external magnetic field, depending on the sign of the magnetic anisotropy ͑for liquid crystals in the mesophase, the sign is given by the difference between magnetic susceptibilities ʈ -Ќ parallel and perpendicular to the director n͒. A high magnetic anisotropy is required to obtain a low threshold of the magnetic field causing the magnetic alignment.…”

“…The latter is particularly important in designing lanthanide-containing metallomesogenes with a very high magnetic anisotropy required for their easy alignment in a weak magnetic field. [10][11][12][13][14] An additional aim of this paper is to examine in some details the validity of the Bleaney approach in the description of the roomtemperature magnetic anisotropy for real lanthanide complexes in which the ⌬E CF splitting energy is normally larger than the thermal energy k B T. We revise the general conclusions of the Bleaney theory on the basis of the results of our numerical calculations of the anisotropic magnetic susceptibility for model lanthanide complexes with various types of the coordination polyhedra.…”

“…In contrast to the 3 Ϫ 1 quantity, which is always positive, the magnetic anisotropy defined in such a way may be both positive and negative, as observed in lanthanide-containing liquid crystals. 11,12 The sign of ⌬ is also important in analyzing the paramagnetic shifts in NMR spectra of lanthanide ions. 16 -20 Throughout the paper, ⌬ is expressed in units of 10 Ϫ6 cm 3 mol Ϫ1 .…”