Lesson plan
Spin crossover
Spin crossover (SCO) is a phenomenon that occurs in some metal complexes wherein the spin state of the complex changes due to an external stimulus. The stimuli can include temperature, pressure or radiation. Spin crossover is referred to as spin transition if takes place suddenly,or spin equilibrium, when is gradual. However, this terminology is not strict, the "cross-over" and "transition" being often considered equivalent. The change in spin state usually involves transformation from a low spin (LS) ground state (at low temperatures and/or high pressure) towards a high spin (HS) ground configuration (at high temperature or reduced/normal pressure). Spin crossover is commonly observed with first row transition metal complexes with a d 4 through d 7 electron configuration in an octahedral ligand geometry. Spin transition curves typically plot the high-spin molar fraction against temperature. The abruptness with hysteresis indicates cooperativity, or "communication", between neighboring metal complexes, throughout the whole lattice. A transparent account of cooperative lattice effects is the mechano-elastic model of spin transition, developed in terms of volume changes of molecular units, along the spin state swap and intermolecular effects assumed as harmonic oscillators. The spin crossover, or spin transition is a neat example of bi-stability.…
Article summary
Spin crossover (SCO) is a phenomenon that occurs in some metal complexes wherein the spin state of the complex changes due to an external stimulus. The stimuli can include temperature, pressure or radiation. Spin crossover is referred to as spin transition if takes place suddenly,or spin equilibrium, when is gradual. However, this terminology is not strict, the "cross-over" and "transition" being often considered equivalent. The change in spin state usually involves transformation from a low spin (LS) ground state (at low temperatures and/or high pressure) towards a high spin (HS) ground configuration (at high temperature or reduced/normal pressure). Spin crossover is commonly observed with first row transition metal complexes with a d 4 through d 7 electron configuration in an octahedral ligand geometry. Spin transition curves typically plot the high-spin molar fraction against temperature. The abruptness with hysteresis indicates cooperativity, or "communication", between neighboring metal complexes, throughout the whole lattice. A transparent account of cooperative lattice effects is the mechano-elastic model of spin transition, developed in terms of volume changes of molecular units, along the spin state swap and intermolecular effects assumed as harmonic oscillators. The spin crossover, or spin transition is a neat example of bi-stability.…
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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