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Chemistry · Glossary

What is Spin crossover?

Definition 18.23 University Chemistry — Year 3 · Chapter 18 — Electronic Spectra and Magnetism of Complexes

Spin crossover is the conversion of a complex between a low-spin and a high-spin state with temperature, pressure or light, possible when Δo\Delta_{\mathrm o} is close to the pairing energy.

Left: _ mT against T for a Curie paramagnet (S = 5/2, g = 2: constant 4.38\, cm3\, K\, mol-1) and for a model iron(II) spin-crossover compound (H = 15\, kJ/ mol, S = 75\, J\, K-1\, mol-1), which goes from 0 (low spin, S = 0) to 3.0\, cm3\, K\, mol-1 (high spin, S = 2). Right: the Curie law, _ m linear in 1/T.
Left: χmT\chi_{\mathrm m}T against TT for a Curie paramagnet (S=52S = \frac52, g=2g = 2: constant 4.38 cm3 K mol−14.38\,\mathrm{cm}^{3}\,\mathrm{K}\,\mathrm{mol}^{-1}) and for a model iron(II) spin-crossover compound (ΔH=15 kJ/mol\Delta H = 15\,\mathrm{kJ}/\mathrm{mol}, ΔS=75 J K−1 mol−1\Delta S = 75\,\mathrm{J}\,\mathrm{K}^{-1}\,\mathrm{mol}^{-1}), which goes from 0 (low spin, S=0S = 0) to 3.0 cm3 K mol−13.0\,\mathrm{cm}^{3}\,\mathrm{K}\,\mathrm{mol}^{-1} (high spin, S=2S = 2). Right: the Curie law, χm\chi_{\mathrm m} linear in 1/T1/T.
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