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Cooperative effects in the [Fe(mtz)6](BF4)2 spin-crossover system: fine tuning the energy gap

Hinek, Roland
Gutlich, Philipp
Published in Inorganic chemistry. 1994, vol. 33, no. 3, p. 567 - 572
Abstract In the [Fe(mtz)6] (BF4)zspin-crossover system, the Fe(I1) complexes occupy two nonequivalent lattice sites. Complexes on lattice site A show a thermal high-spin (HS) - low-spin (LS) transition at 74 K, whereas complexes on site B remain in the high-spin state down to 10 K. Complexes on both sites exhibit light-induced spin-state conversions at 20 K: LS - HS on site A after irradiation at 514.5 nm; HS - LS on site B after irradiation at 830 nm. The subsequent relaxation processes are strongly influenced by cooperative effects of elastic origin, leading to characteristic deviations from first-order kinetics. This is attributed to a buildup of an internal pressure during the relaxation process, giving rise to a shift in both the horizontal (bond length difference AQL) and the vertical (energy gap A,?$,,) displacements of the potential wells of the two states relative to each other. The shifts can be estimated from the observed shift of the d-d absorption bands on the order of 100 cm-I. For site B complexes, this may lead to a change in the true ground state.
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HINEK, Roland, GUTLICH, Philipp, HAUSER, Andreas. Cooperative effects in the [Fe(mtz)6](BF4)2 spin-crossover system: fine tuning the energy gap. In: Inorganic chemistry, 1994, vol. 33, n° 3, p. 567 - 572. doi: 10.1021/ic00081a027

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