CONVERSION OF LOW SPIN STATES IN A MONOCHELATE COMPLEX OF Fe(III) WITH AN ASYMMETRIC TRIDENTATE AZOMETHINE LIGAND
M. S. Gruzdev, N. E. Domracheva, A. I. Aleksandrov, V. P. Osipova, U. V. Chervonova, A. M. Kolker, T. V. Pashkova, D. V. Barakhtenko
Keywords: Fe(III) complexes, Schiff base, electron paramagnetic resonance, structure, mass spectrometry, IR spectroscopy, dimer, hydrogen bond, supramolecular packing
Abstract
An iron(III)-containing complex with the asymmetric tridentate azomethine ligand 4,4'-dodecyloxy-benzoyloxybenzoyl-4-salicylidene-N'-ethyl-N-ethylenediamine with a PF6- counterion is obtained. The presence of the complexing ion is confirmed by far IR Fourier spectra. The structure of the compounds is determined by matrix-assisted laser desorption/ionization with a time-of-flight mass analyzer (MALDI-ToF). The results of mass spectrometric studies are consistent with the elemental analysis data. It is found that the complexation of iron salt with an asymmetric tridentate ligand results in the formation of compounds of the composition 1:1 with octahedral packing of a metal ion in the complex. The electrochemical behavior of the compound in organic solvents is examined. The EPR study shows that iron(III) ions are in both low spin (LS) and high spin (HS) states in the complex. The LS and HS iron(III) centers are coupled into dimers in which a water molecule and the PF6- counterion act as bridges. It is also found that for LS complexes in the low-temperature phase (4.2-300 K), the (dxz, dyz)4(dxy)1 electronic state is the ground state. It is revealed that the conversion of the sample into a high-temperature liquid crystalline (387-405 K) phase is accompanied by the conversion of the LS states of the Fe(III) ion: (dxz, dyz)4(dxy)1 ↔ (dxy)2(dxz, dyz)3. The conversion of LS states is temperature reversible and is driven by the temperature. X-ray crystallographic data confirm that the compound obtained consists of dimer formed by a hydrogen (O–H⋯F) bond.
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