Structure determination and investigation of the high-spin .tautm. low-spin transition of tris[2-(aminomethyl)pyridine]iron(2+) dibromide.monoethanol

Photoexcitation in the Spin-Crossover Compound [Fe(pic)3]Cl2·EtOH (pic = 2-Picolylamine)

“…They suggest that at temperatures of 10 K or below, the quantum efficiency of the photoconversion from the low-spin to the high-spin state depends on the excitation light intensity, and they report values for the quantum efficiency of this process, that is, the number of iron complexes converted per absorbed photon, of up to 34. This value is different from the value of approximately unity reported for another typical spin-crossover compound, namely, [Fe(ptz) 6 ]-(BF 4 ) 2 (ptz ) 1-propyltetrazole), 11 that shows relaxation behavior that is quite similar to that of the title compound. Our independent determination of the quantum efficiency and its dependency on temperature as well as on light intensity, presented in the following discussion, does not confirm the observations reported by Ogawa et al 10 …”

“…On average, ∆r HL ) r HS -r LS is ∼0.18 Å, 5 and the corresponding volume difference ∆V HL , corrected for thermal contraction, is ∼9 Å 3 . 6 In spin-crossover compounds, the high-spin state can also be populated quantitatively as a metastable state below the thermal transition temperature by irradiating into either ligandfield or MLCT absorption bands of the low-spin species. This is the so-called light-induced excited spin state trapping (LIESST) effect, 4 in which, according to Scheme 1, an extremely rapid 7 double intersystem crossing step takes the complex from the initially excited state to the high-spin state.…”

Calculation of the lattice deformation at the phase transitions of [Fe(ptz)6](BF4)2from powder diffraction patterns

“…In this work we have derived strain tensor elements describing the lattice deformation due to a spin transition and to thermal expansion from powder diffraction data. The accuracy of the evaluated deformation tensor elements is comparable with those obtained from the absolute values of the temperature-dependent lattice parameters recently determined from single-crystal measurements on the spin transition compounds [Fe(2-pic)a]X2.Sol (2-pic = 2-picolylamine = 2-aminomethylpyridine, X = C1, Br, Sol = EtOH, MeOH) with a four-circle diffractometer (Wiehl et al, 1986;Adler et al, 1987). This accuracy could be reached because relative differences of peak positions rather than absolute values -were used and because the equations could be separated such that the symmetry-conserving and the symmetry-breaking tensor elements were determined independently from different features of the powder diagrams.…”

“…The experimental task was then to derive this deformation tensor from the temperature dependence of lattice parameters. In the case of the picolylamine compounds (Wiehl et al, 1986;Adler et al, 1987) this could be performed in an easy way, as the lattice parameters a,(T) proved to depend linearly on the HS fraction yHs(T) times a temperature-independent deformation tensor. The results indicated that not only the volume change, represented by the trace of the tensor, but that all tensor components are necessary to account for the true magnitude of the elastic interaction energy.…”

Assessment of Density Functionals for the High‐Spin/Low‐Spin Energy Difference in the Low‐Spin Iron(II) Tris(2,2′‐bipyridine) Complex

“…Experimentally, this has been evidenced by a change of the crystal volume associated with the spin transition of 15-30 3 per molecular unit. [8,[12][13][14] Such a large difference of the molecular volume makes the spin-crossover phenomenon sensitive to external pressure as well as to variations in the second coordination sphere, [15] and it is responsible for the cooperative effects often observed in neat spin-crossover compounds.…”