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Cyanocarbanion-based spin-crossover materials: photocrystallographic and photomagnetic studies of a new iron(II) neutral chain

Abstract : A new iron(II) chain of formula [Fe(abpt)(2)(tcpd)] [1; (tcpd)(2-) = [C(10)N(6)](2-) = (C[C(CN)(2)](3))(2-) = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion, abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole] has been synthesized and characterized by IR spectroscopy, detailed variable-temperature single-crystal X-ray diffraction, magnetic and photomagnetic measurements. The crystal structure determination of 1 reveals a one-dimensional structural architecture in which the (tcpd)(2-) cyanocarbanion acts as a μ(2)-bridging ligand and the two abpt molecules act as chelating ligands. Detailed X-ray diffraction studies as a function of the temperature (293-10 K) showed a strong modification of the iron coordination sphere, whose characteristics are in agreement with the presence of a spin-crossover transition from high spin (HS) to low spin (LS) in 1. The average Fe-N distances at room temperature, at 10 K following a flash cooling, and at 10 K after subsequent HS-to-LS relaxation are in the range expected for 100%, 50%, and 25% fractions of HS Fe(II), respectively. These observations are consistent with the presence of ca. 25% residual HS species at low temperatures, as derived from the magnetic data. The signature of a photoinduced metastable HS state in 1 has been detected by performing coupled photomagnetic and photocrystallographic analyses. The limiting T(LIESST) value associated with the light-induced excited-spin-state trapping effect was derived as 35 K, in good agreement with the thermal dependence of the unit cell volume upon irradiation. Kinetic studies governing the photoinduced HS/LS process have been recorded at different temperatures; a reverse-LIESST effect has been evidenced at 10 K as a reduction of the residual HS fraction by irradiating the sample at 830 nm.
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https://hal.archives-ouvertes.fr/hal-00545079
Contributor : Stéphane Toulin <>
Submitted on : Thursday, December 9, 2010 - 3:24:01 PM
Last modification on : Wednesday, July 15, 2020 - 10:30:02 AM

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Gaelle Dupouy, Smail Triki, Mathieu Marchivie, Nathalie Cosquer, Carlos J. Gómez-García, et al.. Cyanocarbanion-based spin-crossover materials: photocrystallographic and photomagnetic studies of a new iron(II) neutral chain. Inorganic Chemistry, American Chemical Society, 2010, 49 (20), pp.9358-68. ⟨10.1021/ic101038z⟩. ⟨hal-00545079⟩

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