Temperature-dependent laser flash photolysis experiments on the low-spin iron(II) systems [M1−xFex(bpy)3](PF6)2 (M=Cd, Mn and Zn,x≈0.01, bpy=2,2′-bipyridine) under external pressure are presented. Below 50 K the high-spin→low-spin relaxation is an almost temperature-independent tunnelling process. Above that temperature it tends towards a thermally activated behaviour. A change of the host from cadmium to zinc results in an increase of the low-temperature tunnelling rate constant by two orders of magnitude. An external pressure of 1 kbar accelerates the low-temperature tunnelling process by a factor of 2. [Mn1−xFex(bpy)3](PF6)2 and [Zn1−xFex(bpy)3](PF6)2show a phase transition at ≈1.1 kbar, which increases the tunnelling rate by a factor of about 6.
  • High-spin -> low-spin relaxation in [Zn1-xFex(6-mepy)3-y(py)ytren](PF6)2
    S. Schenker, A. Hauser, W. Wang and I.Y. Chan
    Journal of Chemical Physics, 109 (22) (1998), p9870-9878
    DOI:10.1063/1.477681 | unige:2763 | Abstract | Article PDF
The thermal spin transition in the diluted mixed crystal [Zn1−xFex(6-mepy)3tren](PF6)2 (x = 0.00025, (6-mepy)3tren = tris{4-[(6-methyl)-2-pyridyl]-3-aza-3-butenyl}amine) is studied at 1 bar and 1 kbar by temperature-dependent absorption spectroscopy. From thermodynamic analysis of the high-spin (HS) fractions, values for ΔHHL0 and ΔSHL0 of 1551(50) cm−1 and 7.5(5) cm−1/K and a molecular volume of reaction, ΔVHL0, of 22(2) Å3result. Reconsideration of the cooperative effects in the neat [Fe(6-mepy)3tren](PF6)2from Adler et al. [Hyperfine Interact. 47, 343 (1989)] result in a lattice shift, Δ, of 208(15) cm−1 and an interaction constant, Γ, of 109(15) cm−1. Temperature-dependent laser flash photolysis experiments in the spin-crossover system [Zn1−xFex(6-mepy)3tren](PF6)2 and the LS system [Zn1−xFex(py)3tren](PF6)2 in the pressure range between 1 bar and 1 kbar are presented. Above ≈100 K the HS→LS (low-spin) relaxations behave classically, whereas they become almost temperature independent below 50 K. At ambient pressure, the low-temperature tunneling rate constant in[Zn1−xFex(py)3tren](PF6)2 is more than three orders of magnitude larger than the one in[Zn1−xFex(6-mepy)3tren](PF6)2. External pressure of 27 kbar accelerates the low-temperature tunneling process by almost nine orders of magnitude. The kinetic results are discussed within the theory of nonadiabatic multiphonon relaxation.
  • Pressure effects on the HS -> LS relaxation in [Zn1-xFex(6-mepy)3tren](PF6)2
    W. Wang, I.Y. Chan, S. Schenker and A. Hauser
    Journal of Chemical Physics, 106 (9) (1997), p3817-3820
    DOI:10.1063/1.473436 | unige:2789 | Abstract | Article PDF
Laser flash photolysis experiments were performed on the mixed crystal [Zn1−xFex(6-mepy)3tren](PF6)2 (x=0.00025) at 10 K in the pressure range between 1 bar and 20 kbar. An external pressure of 20 kbar accelerates the low-temperature tunneling process by almost eight orders of magnitude.



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