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Title

Cooperative phenomena and light-induced bistability in iron(II) spin-crossover compounds

Authors
Romstedt, Harald
Hinek, Roland
Spiering, Hartmut
Published in Coordination Chemistry Reviews. 1999, vol. 190-192, no. 36, p. 471-491
Abstract In iron(II) spin-crossover compounds, the transition from the 1A1 low-spin state at low temperatures to the 5T2 high-spin state at elevated temperatures is accompanied by a large increase in metal-ligand bond lengths. The resulting elastic interactions may be pictured as an internal pressure which is proportional to the concentration of the low-spin species. Because pressure stabilises the low-spin state relative to the high-spin state this results in a positive feedback. Thermal transition curves in neat iron(II) spin-crossover compounds are thus invariable much steeper than in diluted mixed crystals, and the high-spin→low-spin relaxation following the light-induced population of the high-spin state at low temperatures is self-accelerating. Strong interactions give rise to a thermal hysteresis, and light-induced bistabilities may be observed for compounds with initially a high-spin ground state and the potential for a light-induced population of the low-spin state. For such compounds, the increasing internal pressure may stabilise the low-spin state sufficiently so that it becomes the molecular ground state above some critical light-induced low-spin fraction. Secondary effects of the elastic interactions include crystallographic phase transitions, inhomogeneous distributions of sites, and anomalies such as steps in the transition curve.
Keywords Iron(II) coordination compoundsSpin-crossoverCooperative effectsHigh-spinlow-spin relaxationBistability
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Research group Groupe Hauser
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HAUSER, Andreas et al. Cooperative phenomena and light-induced bistability in iron(II) spin-crossover compounds. In: Coordination Chemistry Reviews, 1999, vol. 190-192, n° 36, p. 471-491. https://archive-ouverte.unige.ch/unige:2740

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Deposited on : 2009-09-21

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