EPR of the first Fe(III)-containing spin-crossover metallomesogens
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The low-spin (LS) to high-spin (HS) transition in two mesogenic Fe(III) complexes with alkyloxysalicyliden-N′-ethyl-N-ethylendiamine as ligands is studied by electron paramagnetic resonance (EPR). The symmetrization of the crystal field around the Fe(III) ion under first heating of a polycrystalline sample from the room temperature was observed in the spectra of HS complexes. The line narrowing (from 45 to 15 mT) under the crystal-smectic phase transition is explained by the strengthening of the intermolecular exchange interaction, as a result of the structural reorganization of layers in the smectic phase. A feature of both mesogenic spin-transition systemsis an unusual field-induced spin instability which leads to the hysteresis of the HS-LS composition. This instability is detected by EPR and magnetic susceptibility methods. The alignment of systems by magnetic field in the mesophase and a complete or partial orientational order under cooling the mesophase to the glass state are the main reason for this hysteresis. The influence of EPR-silent LS complexes reveals itself in the line broadening of HS compounds’ when the temperature is lowered from 220 K.
KeywordsElectron Paramagnetic Resonance Electron Paramagnetic Resonance Spectrum Electron Paramagnetic Resonance Line Smectic Phase Ethylsulphate
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