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  • 1
    Electronic Resource
    Electronic Resource
    Thermal and light-induced spin transition in [Fe(bpen)X2] (bpen = 1,6-Bis(2-pyridyl)-2,5-diazahexane, X = NCS-, NCSe-)Dedicated to Professor Max Herberhold on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1129-1133 
    Details
    ISSN: 0947-6539
    Keywords: iron complexes ; kinetics ; magnetic susceptibility ; Mössbauer spectroscopy ; spin crossover ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal and light-induced spin transitions in [Fe(bpen)(NCS)2] and [Fe(bpen)(NCSe)2] have been investigated by means of magnetic susceptibility and Mössbauer measurements. The HS → LS transition in [Fe(bpen)(NCS)2] is detected at temperatures below 120 K (T1/2 [when the fraction of high-spin species γHS = 0.5] = 68 K) with a residual HS fraction of 8% at 20 K. The transition is fairly abrupt and no hysteresis is observed, in contrast to earlier studies (ref. [8]). The generation of metastable HS states in [Fe(bpen)(NCS)2] is achieved by rapid cooling of the sample and by irradiating the compound at low temperatures with light of appropriate wavelengths (LIESST). The HS → LS relaxation of the metastable spin states after rapid cooling is observed at temperatures between 35 and 42.5 K and shows strong deviations from single exponential behavior. The spin-transition behavior changes drastically on substitution of the thiocyanate ions by NCSe-. In [Fe(bpen)(NCSe)2] a gradual and complete spin transition between 140 and 250 K is observed (T1/2 = 181 K). Irradiation of the compound with green light at low temperatures does not result in formation of long-lived metastable HS states. The spintransition curves derived from magnetic susceptibility and Mössbauer studies show good agreement for each compound, and no hints of significantly different Lamb-Mössbauer factors for the HS and LS states are observed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020912
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  • 2
    Electronic Resource
    Electronic Resource
    High-spin → low-spin relaxation in [Fe(bpp)2](CF3SO3)2 H2O after LIESST and thermal spin-state trapping - dynamics of spin transition versus dynamics of phase transitionDedicated to Professor Gerhard Herberich on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1134-1138 
    Details
    ISSN: 0947-6539
    Keywords: iron complexes ; magnetic susceptibility ; Mössbauer spectroscopy ; phasetransitions ; spin crossover ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The iron(II) complex [Fe(bpp)2]-(CF3SO3)2 H2O (bpp = 2,6-bis(pyrazolyl-3-yl)pyridine) shows a thermal spin transition associated with a hysteresis of approximately 140 K width. The transition temperatures T1/2 (where the fraction of HS species γHS = 0.5) are 147 K and ≍285 K in the cooling and heating directions, respectively. The compound shows the LIESST and reverse-LIESST effects at low temperatures. The relaxation of the metastable HS states generated by LIESST was observed quantitatively at temperatures between 77.5 and 85 K by Mössbauer spectroscopy. Metastable HS states can also be generated by rapid cooling of the sample. The relaxation of the metastable HS states formed by thermal spin-state trapping was monitored at temperatures between 104 and 118 K by magnetic susceptibility measurements. The relaxation mechanisms of the HS states generated by LIESST and thermal spinstate trapping are completely different. We suggest that the HS → LS relaxation after thermal spin-state trapping is triggered by an additional structural phase transition of the system.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020913
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