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Normal Spinels

Spinel is the name given to the mineralMgAl₂O₄. It has a common structuralarrangement shared by many oxides of the transition metalswith formula AB₂O₄.
In thenormal pattern the oxygens (red) form acubic close packed (ABCABC or face centred) array and theMg(II) (A(II)-green) and Al(III) (B(III)-silver) sit in tetrahedral(1/8 occupied) and octahedral (1/2 occupied) sites in the lattice, givinga Unit Cell with 8 Mg's, 16 Al's and 32 O's.
Aninverse spinel is analternative arrangement where the divalent ions swap withhalf of the trivalent ions so that theM(II) now occupy octahedral sites
i.e. B(AB)O₄.

Complexes that share this structure include..
many of the first row TM oxides and sulfides

The display shows an idealised unit cell (Space group 216 F-43m).The cubic cell lengths used were a=b=c=8.0858A.These are not the usual values quoted and come from what seems to bean overlooked paper in Proc. Roy. Soc., 1983, 386, 333-245.Their crystallographic evidence suggests that a better fit of the datacomes from F-43m, rather than theoften quoted Fd3m centrosymmetric space group.
One method of predicting whether a structure will be normal or inverseis to calculate Octahedral Site Preference Energies for both the A(II)and B(III). The ion with the more stable energy is predicted to fit intothe octahedral site.
However, see J. Am. Chem. Soc., 1982, 104, 92-95 for a differentmethod that does NOT involve OSPE calculations.

For alternate views of spinels,

and check out the following sites;Wellesley Collegeand theUniversity of Le Mans.

Information is available to show how theindividual structural pages were created.
Return to thestructure of binary salts introductory page.

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Created and maintained by Prof. Robert J.Lancashire,
The Department of Chemistry, University of the West Indies,
Mona Campus, Kingston 7, Jamaica.Created March 2000. Links checked and/or last modified27th November 2014.
URLhttp://wwwchem.uwimona.edu.jm/courses/spinel.html

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