The mineral magnetite has the formula Fe3O4 and has an inverse spinel structure. In the unit cell, there are two Fe ions in octahedral sites and one Fe ion in a tetrahedral site. (i) Are the Fe ions in magnetite low-spin or high-spin? Explain your reasoning. (ii) Draw d-orbital splitting diagrams for Fe(III) in tetrahedral and octahedral ligand fields and hence deduce the CFSE in each case. (iii) On the basis of your answer to part (ii) above, do you expect Fe(III) to have a preference for tetrahedral or octahedral sites? Explain your answer.
The mineral magnetite has the formula Fe3O4 and has an inverse spinel structure. In the unit cell, there are two Fe ions in octahedral sites and one Fe ion in a tetrahedral site.
(i) Are the Fe ions in magnetite low-spin or high-spin? Explain your reasoning.
(ii) Draw d-orbital splitting diagrams for Fe(III) in tetrahedral and octahedral ligand fields and hence deduce the CFSE in each case.
(iii) On the basis of your answer to part (ii) above, do you expect Fe(III) to have a preference for tetrahedral or octahedral sites? Explain your answer.
(iv) Draw d-orbital splitting diagrams for Fe(II) in tetrahedral and octahedral ligand fields and hence deduce the CFSE in each case.
(v) Assuming that Δt ~ 4/9 Δo and using your answer to part (iv) above, deduce the CFSE of Fe(II) in a tetrahedral field in terms of Δo. Hence decide whether the tetrahedral site is occupied by Fe(II) or Fe(III), explaining your reasoning.
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