Spinels, mixed metal oxides, explained in simple terms. Includes calculation method for CFSE and prediction for normal and inverse spinel.

1. - Mixed metal oxides.
- Cubic close packed system, cubic sites occupied by oxide
ligand, which are weak field ligands.
- Contain tetrahedral and octahedral holes Based on type of
metal atom occupying them, they are classified into two
types
- i. Normal Spinels
- Ii. Inverse Spinels or antispinels

2. » A+n represents a metal atom of charge +n
occupying a tetrahedral site.
» B+m represents a metal atom of charge +m
occupying an octahedral site.

3. » Bivalent ions occupy tetrahedral sites, trivalent
ions occupy octahedral sites.
» General Formula :
» A+2B2
+3 O4 OR (AII)tet(BIII)2
octO4
» E.g Mn3O4 (i.e Mn+2Mn2
+3O4 )
» MgAl2O4 (known as spinel), ZnFe2O4,
FeCr2O4 (chromite) etc.

4. » All bivalent cations and half the trivalent cations
in octahedral holes. The other half of trivalent
cations are in tetrahedral holes.
» General Formula B+2B+3A+3O4 or
(BII)oct(BIII )oct(AIII)tetO4

5. » Since Oxide ions are weak field ligands, the
cations are found in high spin configurations.
» Finding out whether a given spinel is normal or
inverse, can be done by calculating CFSE for
both cases.
» Greater the CFSE, more stable the structure and
hence the spinel takes that structure.

6. » Value of 10Dq for a trivalent cation is 1.5 times
more than that of a bivalent ion of the same
element.
» Value of 10Dq is reduced by a factor of 4/9 on
going from an octahedral (B) site to a
tetrahedral site.

7. Config
CFSE d4 d5 d6 d7
Oct (B+2) 6 0 4 6
Oct (B+3) 9 0 6 9
Tet (A+2) 4/9x4 0 4/9x6 4/9x12
Tet (A+3) 2/3x4 0 2/3x6 2/3x12

8. » Predict spinel structure for
i. Mn3O4
ii. Fe3O4
iii. Co3O4