High-Temperature Spin Crossover in Complexes of Iron(II) closo -Borates with 2,6-Bis(benzimidazol-2-yl)pyridine
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High-Temperature Spin Crossover in Complexes of Iron(II) closo-Borates with 2,6-Bis(benzimidazol-2-yl)pyridine A. D. Ivanovaa, L. G. Lavrenovaa, b, *, E. V. Korotaeva, S. V. Trubinaa, L. A. Sheludyakovaa, S. A. Petrovc, K. Yu. Zhizhind, and N. T. Kuznetsovd aNikolaev
Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia b Novosibirsk National Research State University, Novosibirsk, 630090 Russia c Institute of Solid State Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630128 Russia d Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected] Received June 17, 2020; revised June 24, 2020; accepted June 26, 2020
Abstract—New iron(II) complexes with 2,6-bis(benzimidazol-2-yl)pyridine (L) and closo-borate(2–) anions—[FeL2][B10H10] ⋅ 2H2O and [FeL2][B12H12] ⋅ H2O—have been synthesized. The complexes have been characterized by static magnetic susceptibility measurements, electronic (diffuse reflectance spectra), IR, and EXAFS spectroscopy, and X-ray diffraction analysis. A study of the μeff(T) dependence in the temperature range 80–500 K has shown that the complexes exhibit a high-temperature spin crossover 1А1 ⇔ 5Т2. Keywords: synthesis, complexes, iron(II), 2,6-bis(benzimidazol-2-yl)pyridine, cluster boron anions, electronic, IR, and EXAFS spectroscopy, XRD, spin crossover DOI: 10.1134/S0036023620110078
Spin crossover (SCO, spin transition) can manifest itself in 3d4–3d7 metal complexes with an octahedral or pseudo-octahedral environment of ligands of a certain field strength. The change in the spin multiplicity occurs in response to external stimuli: change in temperature and pressure, irradiation with light of a certain wavelength, and other factors. Monographs and numerous reviews and articles [1–9] have been devoted to the study of this phenomenon. Compounds capable of existing in two states with a sufficiently long lifetime are promising for use as active elements in electronic devices [3, 10–15]. One of the classes of compounds in which a spin crossover is observed includes octahedral iron(II) complexes with polynitrogen-containing heterocyclic ligands forming the FeN6 coordination core. In a number of such compounds, thermally induced SCO is observed. The temperature and nature of the spin transition in these complexes depend on a number of factors, in particular, on their structure, the nature of the ligand and anion, the presence and number of crystallization solvent molecules, e.g., water, in the structure. It should be especially noted that the SCO temperature significantly depends on the anions occupying the outersphere position in these complexes. In the present work, 2,6-bis(benzimidazol-2yl)pyridine (L) (Scheme 1) has been used as a ligand for the synthesis of complexes. Before the beginning of our work, only a few iron(II) compounds with L were
known to possess SCO, in particular, Fe(II) perchlorate and tetraphenylborate complexes of [
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