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## Crystal Field theory (CFT)

Crystal Field Theory (CFT) for Octahedral complexes

### The important point of CFT:

1. This theory considered the metal-ligand bond is purely ionic
2. The electrostatic interaction between metal ion and ligands
3. The ligand is anion metal atom is cation
4. If the ligand is neutral molecule the negative ends of the dipole is attracted towards the metal atom
5. It treats the ligand is a point of negative charge
6. The arrangement of ligand around the central metal ion in such a way that repulsion should be minimum

### Lets For example :

When ligand approaches metal ion (D-Orbitals), The ligand orbitals approach

to D-orbitals of metal. Therefore there will be possible forces

• Force of attraction

It will decrease the force if there will be more force of attraction. it means

there is low energy.

• Force of repulsion

It will increase the force if there will be more force of attraction. it means

there is high energy.

There are 5 D-orbitals in metal ion

Shape and Orientation of 5 D-orbitals in metal ion

In below image you can see, there are 5 types of D-orbitals

dz2, dxy, dxz, dyz , and dx2y2

### Important Point

when ligand approaches the metal ion (d-orbitals)

ligand does not equally affect all d-orbitals of metal ion

due to the orientation of orbital.

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### Let me explain

dx2-dy2 and dz2 will be more effective

however

dxy  dyz  dxz will be less effective

In the diagram, you can see

there is low repulsion in dxy  dyz  dxz then dx2-dy2 and dz2

0 = Crystal field splitting energy

the magnitude of ∆0 depends upon types of ligands

for example

strong fiends ligands (NH3) = more splitting (High value of ∆0)

Weak fields ligands (H2O) = less splitting (Low value of ∆0)

Properties Explained by Crystal Field Theory

Here CFT explain how we can arrange the electrons in D orbital

1. High spin and low spin state
2. Magnetic properties
3. Colour

If ∆0 < P, the 4th electron will enter eg thus we get high spin complexes

If ∆0 > P, the 4th electron (up to d6) will enter t2g thus we get low

spin complexes

let’s explain with Fe+2

Fe+2 = d6

in the above diagram, Fe+2

Weak field ligand for H2O and strong field ligand for NH3

Crystal Field Theory (CFT) for Octahedral complexes

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