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Bis(pyrazolato) Bridged Diiron Complexes: Ferromagnetic Coupling in a Mixed‐Valent HS‐FeII/LS‐FeIII Dinuclear Complex

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Ye,  Shengfa
Research Group Ye, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Citation

Wong, J. W. L., Hua, S.-A., Demeshko, S., Dechert, S., Ye, S., & Meyer, F. (2020). Bis(pyrazolato) Bridged Diiron Complexes: Ferromagnetic Coupling in a Mixed‐Valent HS‐FeII/LS‐FeIII Dinuclear Complex. European Journal of Inorganic Chemistry, 2020(43), 4137-4145. doi:10.1002/ejic.202000697.


Cite as: https://hdl.handle.net/21.11116/0000-0007-7B1C-1
Abstract
Using a new bis(tridentate) compartmental pyrazolate‐centered ligand HL, the bis(pyrazolato)‐bridged diiron complex [L2FeII2][OTf]2 (1) and its singly oxidized mixed‐valent congener [L2FeIIFeIII][OTf]3 (2) have been synthesized and structurally characterized. While 1 features two HS‐FeII ions coordinated to two cis‐axial pyridine moieties in a highly distorted octahedral environment, the metal ions in 2 are coordinated by the ligand strand in a trans‐axial configuration. Very different Fe–N bond lengths and distinctly different coordination polyhedra are associated with pronounced valence localization in the case of 2. The electronic structures and magnetic properties of 1 and 2 have been further investigated by Mössbauer spectroscopy and variable temperature magnetic susceptibility measurements. In the case of 1, weak antiferromagnetic coupling is observed between the two HS‐FeII ions (J = –0.6 cm–1), while the HS‐FeII and LS‐FeIII ions in 2 are ferromagnetically coupled (J = +5.2 cm–1) to give an ST = 5/2 ground state with significant zero‐field splitting (DFe(II) = 2.3 cm–1). The findings are rationalized with the help of DFT computations.