Study Notes on Spinels
Structure of spinels:
Spinels have the general chemical formula AB2X4. Here,
AII- a divalent cation like Mn, Cr, Fe, Co, Ni
BIII- a trivalent cation like Ga, Al, Cr, Mn, Fe
Mixed metal oxides having the composition AIIB2III O4 are called spinels. A and B may be different metals or the same metal in different oxidation states. Spinels are classified into two types: normal spinels, AII[B2III]O4 inverse spinels, BIII[AII BIII]O4. In normal spinels, A occupies tetrahedral interstices, while B occupies octahedral interstices. The compound NiAl2O4 is an example of normal spinel. In inverse spinels, half B's occupy tetrahedral sites and half B's octahedral sites, while A is in octahedral interstices. An example of an inverse spinel is Fe3O4, when it may be represented as, FeIII[FeIIFeIII]O4.
For transition metal oxide spinels, the choice of the normal and inverse spinels is generally driven by the CFSE of ions in the tetrahedral and octahedral sites. For spinels containing 3d elements like Mn, Fe, Cr and Co, the electronic configuration is typically high spin because O2- is a weak field ligand.
Whether a particular spinel will acquire normal structure or inverse structure largely depends on CFSE. That structure prevails which has a greater negative value of CFSE. For example, consider the mixed manganese oxide, Mn3O4. If it is a normal spinel, its CFSE may be calculated as follows:
MnII [Mn2III] O4
If it is an inverse spinel, the crystal field stabilization energy may be calculated as follows:
MkIII [MnIIMnIII] O4
The normal spinel has a greater negative CFSE and hence this structure prevails.
Co3+ is a low spin in the field produced by oxide ions.
To boost the preparation of all our users, we have come up with some free video (Live Class) series, free quizzes, previous papers.
Here are the links:
- Daily Free Video Series - Click Here
- Daily Free Quizzes - Click Here
- Attempt CSIR-NET Previous Papers - Click Here
More from us:
- Get Unlimited access to Structured Live Courses and Mock Tests - GRADEUP SUPER
- Get Unlimited access to 20+ Mock Tests-Gradeup Green Card.
~ Keep upvoting this article and share it among your friends.
→ If you have any questions feel free to ask in the comments section below.
Join our Telegram Channel for more updates!
Best of Luck!!
Sahi Prep hai to Life Set Hai!!