STEPWISE MAGNETIC BEHAVIOR OF THE LIQUID CRYSTAL IRON(III) COMPLEX
N. E. Domracheva1, V. E. Vorob’eva1, A. V. Pyataev2, R. A. Manapov2, E. M. Zueva3, M. S. Gruzdev4, U. V. Chervonova4
1Kazan Physical-Technical Institute, Kazan Scientific Center, Russian Academy of Sciences
2Kazan (Volga region) Federal University
3Kazan National Research Technological University
4G. A. Krestov Institute of Solution Chemistry, Russian Academy of Sciences
Keywords: electron paramagnetic resonance (EPR), magnetic properties, spin-crossover, Mössbauer spectroscopy, Fe(III) complexes, Schiff bases, liquid crystals, quantum chemical calculations, DFT
Abstract
EPR and Mössbauer spectroscopy is used to study a new liquid crystal complex of iron(III) with a Schiff base: 4,4'-dodecyloxybenzoyloxybenzoyl-4-oxysalicylidene-2-aminopyridine with a PF-6 counterion. It is shown that Fe(III) ions exist only in the high-spin (HS, S = 5/2) state. It is found that under the influence of temperature the system demonstrates the stepwise behavior of the product of the integrated intensity of EPR lines (I) and temperature (proportional to χТ, where χ is the magnetic susceptibility) with an inflection point at ~80 K. Above 80 K a new EPR spectrum is detected due to the excited S = 2 state and the formation of dimeric molecules (through oxygen bridges) with a strong intramolecular antiferromagnetic exchange interaction J1 = 162.1 cm–1. Below 80 K iron(III) complexes are organized in 1D chains where the exchange value J2 = 2.1 cm–1. At 80 K there is a structural phase transition in the system: the transition from a 1D chain organization of HS Fe(III) centers to dimeric molecules. Based on quantum chemical calculations a model of the binuclear iron(III) complex is proposed.
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