The Hoffman-type coordination compound [Fe(pz)Pt(CN)4]⋅2.6 H2O (pz=pyrazine) shows a cooperative thermal spin transition at around 270 K. Synchrotron powder X-Ray diffraction studies reveal that a quantitative photoinduced conversion from the low-spin (LS) state into the high-spin (HS) state, based on the light-induced excited spin-state trapping effect, can be achieved at 10 K in a microcrystalline powder. Time-resolved measurements evidence that the HS→LS relaxation proceeds by a two-step mechanism: a random HS→LS conversion at the beginning of the relaxation is followed by a nucleation and growth process, which proceeds until a quantitative HS→LS transformation has been reached.
  
  • Light-induced spin-state switching in the mixed crystal series of the 2D coordination network {[Zn1-xFex(bbtr)3](BF4)2}: optical spectroscopy and cooperative effects
    P. Chakraborty, C. Enachescu, A. Humair, L. Egger, T. Delgado, A. Tissot, L. Gune, C. Besnard, R. Bronisz and A. Hauser
    Dalton Transactions, 43 (47) (2014), p17786-17796
    DOI:10.1039/C4DT01728E | unige:42340 | Abstract | Article HTML | Article PDF
Depending on the iron(II) concentration, the mixed crystals of {[Zn1-xFex(bbtr)3](BF4)2}∞, bbtr = 1,4-di(1,2,3-triazol-1-yl)butane, 0.01 ≤ x ≤ 1, show macroscopic light-induced bistability between the high-spin and the low-spin state. In the highly diluted system with x = 0.01 and up to x = 0.31, the photoinduced low-spin state always relaxes back to the high-spin state independent of the initial light-induced low-spin fraction. In the highly concentrated mixed crystals with x = 0.67, 0.87 and 1, the strong cooperative effects coupled to a crystallographic phase transition result in light-induced bistability with decreasing critical light-induced low-spin fraction and increasing hysteresis width for increasing iron(II) concentrations. The lower limit for the light-induced bistability is estimated at x ≈ 0.5.

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