Journal
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY
Volume 2021, Issue 28, Pages 2846-2856Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejic.202100355
Keywords
Spin crossover; Magnetic properties; iron(II) compounds; S-based ligands; Hysteresis
Categories
Funding
- CINVESTAV
- SEP-CONACyT [CB 2016/286346]
- CONACyT [591879]
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The study investigated the effect of chelate ring size on the magnetic properties of thioether-based iron(II) metal complexes by synthesizing and characterizing two types of ligands. The results showed that the complexes were isolated in the high spin state, with orbital contribution to g and zero field splitting. The analysis of structural and electronic parameters helped rationalize the differing magnetic properties of the metal complexes.
To study the effect of the chelate ring size on the magnetic properties of thioether-based iron(II) metal complexes, two ligands have been envisaged, synthesised and characterised. The two ligands correspond to the bidentate benzylpicolylthioether (PySBn) and tetradentate 2,3-bis(((2-pyridylmethyl)thio)methyl)quinoxaline (QuinoxS). Five iron(II) complexes have been synthesised, containing either two bidentate ligands or one tetradentate ligand, and two N-bond NCE co-ligands (E=S, Se or BH3): trans-[Fe-II(PySBn)(2)(NCE)(2)] (1 a-b) and cis-[Fe-II(QuinoxS)(NCE)(2)] (2 a-c), a for E=S, b for E=Se and c for E=BH3. The iron(II) complexes have been characterised by standard techniques, X-ray crystallography (except for complex 1 a) and VT-magnetic measurements in the solid state. X-ray crystallography showed that all the complexes are isolated in the high spin (HS) state, based on the relatively long Fe-L bond lengths, Fe-N>2.0 angstrom and Fe-S approximate to 2.5-2.6 angstrom. VT-magnetic measurements demonstrated that complexes 1 a and 2 a-c are stabilised in the HS-state, showing orbital contribution to g and zero field splitting. However, complexes 1 b shows a relatively abrupt, hysteretic, and incomplete at the low-end spin conversion, with T-1/2 down arrow=92, T-1/2 up arrow=98 K and Delta T-1/2=6 K at 5 K min(-1), moreover, the hysteresis loop is scan rate dependent increasing up to 11 K at 10 K min(-1). An analysis of structural and electronic parameters has been performed to rationalise the differing magnetic properties of the metal complexes, such as metallacycle size, bond lengths and angles, and cis- vs. trans-coordination mode. A comparison with the literature-reported spin crossover iron(II) complexes in N4S2 coordination sphere containing NCE co-ligands has been conducted as well, finding that, as previously reported, the Fe-N-C(E) bond angle is diagnostic for determining the spin lability of the metal complexes, and in addition we have found that the N-C(E) bond length is too useful.
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