Normal Spinels

عضو فضي

Spinel is the name given to the mineral MgAl2O4. It has a common structural arrangement shared by many oxides of the transition metals with formula AB2O4.
In the normal pattern the oxygens (red) form a cubic close packed (ABCABC or face centred) array and the Mg(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, giving a Unit Cell with 8 Mg's, 16 Al's and 32 O's.
An inverse spinel is an alternative arrangement where the divalent ions swap with half of the trivalent ions so that the M(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 be an overlooked paper in Proc. Roy. Soc., 1983, 386, 333-245. Their crystallographic evidence suggests that a better fit of the data comes from F-43m, rather than the often quoted Fd3m centrosymmetric space group.
One method of predicting whether a structure will be normal or inverse is 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 into the octahedral site.
However, see J. Am. Chem. Soc., 1982, 104, 92-95 for a different method that does NOT involve OSPE calculations.
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For alternate views of spinels,

عضو جيد

مشكووووور ع الموضوع العلمي المفيد
تقبل مروري

عضو فضي

تسلمين وان شاء الله الموضوع يفيدكم بشي

عضو جديد

مشكور اخي الزعيم على هذا الموضوع واتمني ممن لديه مراجع او اوراق بحثية بخصوصه (spinel group) ان يفيدني بها لانه جزء مهم من موضوع رسالتي ولكم جزيل الشكر

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