Crystal Field Theory (CFT), developed by Hans Bethe and John Hasbrouk Van Veck in the 1930s, is a bonding model describing the properties of transition metal complexes, such as colors and magnetism. CFT assumes ionic bonds between central metal atoms and ligands, which can be positive, neutral, or negative, and explains the arrangement of ligands to minimize repulsion. Additionally, CFT addresses d-orbital splitting in complexes and is utilized to explain spin states, magnetic properties, and colors of complex compounds.

1. CRYSTAL FIELD THEORY
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2. HISTORY OF CRYSTAL FIELD THEORY
CFT was developed by physicists Hans Bethe and John Hasbrouk van VECK in 1930’s.
CFT was subsequently combined with Molecular Orbital Theory.
CFT is a bonding model that explains many important properties of transition metal
complexes , including their colours, magnetism ,structures , stability etc.

3. FEATURES OF CRYSTAL FIELD THEORY
CFT assume that bonds between central metal atom or ion and ligands are
purely ionic.
Examples of central metal atoms are Cu ,Mg ,Ca etc.
Ligands are of three types positive, neutral, and negative.
Examples of :-
-ve ligands : F-,Cl-,OH-, CN-
+ve ligands :NO+
Neutral : NH3,H20

4. The arrangement of ligands around the central metal atom or ion is such that
the repulsion between these negative points or dipoles are minimum.

5. The forces between metals and ligands are of two types :-
1. Attraction Force :-
positive charge of the central metal atom and negative charge of ligands.
2. Repulsion Force :-
D-electrons of central metal atom and lone pair electrons of ligands.
D-orbitals of central metal atom are divided into two sets depending on their
orientation.
Non-axial orbitals/ t2g orbitals/ three fold degenerate orbitals :-
dxy, dyz, dxz
Axial orbitals/ eg orbitals/ two fold degenerate orbitals :-
dx2-y2, dz2

7. Splitting of d- orbitals in octahedral complex :-

8. Example :-

10. Splitting of d-orbitals in tetrahedral complex :-

12. Example :-

13. Relation between crystal field splitting of tetrahedral and
octahedral complex is :-

14. Uses of Crystal Field Theory :-
1. It can explain high spin and low spin state of coordinate compounds.
2. It can explain magnetic properties of complex compounds.
3. It also explains colour of complex compounds.

15. Pentagonal bipyramidal :-

16. Square antiprismatic :-

17. Sauare planar :-

18. Trigonal bipyramidal :-