Crystal Field Theory i) Separate metal and ligands have high energy ii) Coordinated Metal - ligand get stabilized iii) Metal and Ligands act as point charges. iv) Metal and ligands bond due to strong electrostatic forces of attraction. v) F = q 1 q 2 ( q 1 q 2 – point charges, distance between charges) r 2 vi)Destabilization due to ligand -d electron repulsion

d - orbitals

Ligand-Metal Interaction Basic Assumption in CFT: Electrostatic interaction between ligand and metal d-orbitals align along the octahedral axis will be affected the most. More directly the ligand attacks the metal orbital, the higher the the energy of the d-orbital. In an octahedral field the degeneracy of the five d-orbitals is lifted

Octahedral field

Splitting of d-Orbitals Splitting of d-Orbitals Octahedral Field Ligands approach metal on the axis d-orbitals not pointing directly at axis are least affected (stabilized) by electrostatic interaction d-orbitals pointing directly at axis are affected most by electrostatic interaction

Splitting in Octahedral field Stage I Stage II Stage III Hypothetical

Stage I – The free metal ion. Degenerate d- orbitals. Stage II – Hypothetical stage- 1. The six ligands create a symmetrical uniform field. 2. All the d orbital experience equal repulsion and their energy get raised equally. 3. Degenerate d- orbitals. Stage III – 1.Ligands create an octahedral field and approach on the axis. 2.The e g, d orbitals oriented along the axis (d x2 – y2 and d z2 ) experience greater repulsion and are repelled more. 3.Degeneracy is lost. 4.Splitting of d orbitals take place, Δ o = 10 Dq 5.For every electron entering t 2g orbital energy equal to 4 Dq is released and every electron entering e g orbital raises the energy equal to 6 Dq. Splitting in Octahedral field

Splitting in Tetrahedral field X - axis y - axis z - axis

Splitting in Tetrahedral field Free metal ion Degenerate d - orbitals Free metal ion Spherical field Degenerate d – orbitals Higher energy splitting of d – orbitals CFS = Δ t

Stage I – The free metal ion. Degenerate d- orbitals. Stage II – Hypothetical stage – 1. The four ligands create a symmetrical uniform field. 2. All the d orbital experience equal repulsion and their energy get raised equally. 3. Degenerate d- orbitals. Stage III – 1.Ligands create a tetrahedral field. 2.Ligands approach in between the axis. 3.The t 2g d orbitals oriented in between the axis (d xy, d yz, d xz ) experience greater repulsion and are repelled more. 4.Degeneracy is lost. 5.Splitting of d orbitals take place. Splitting in Tetrahedral field

d x2 – y2 d z2 d xy d xz d yz d x2 – y2 d z2 d xy d yz d xz Δ sp State 1State 2State 3State 4State 5 Splitting in Square Planar field

Stage I – The free metal ion. Degenerate d- orbitals. Stage II – Hypothetical stage – 1. The four ligands create a symmetrical uniform field. 2. All the d orbital experience equal repulsion and their energy get raised equally. 3. Degenerate d- orbitals. Stage III – 1.Ligands create an octahedral field. Ligands approach in between the axis. 2. Splitting of d orbitals take place. Stage IV – Orbitals oriented along the x – axis are moved away from the central metal, hence d xz, d yz and d z2 are lowered in energy. Stage V - Orbitals oriented along the x – axis are removed hence d xz, d yz and d z2 are further lowered in energy and difference in energy between d xy and d x2 –y2 give the crystall field splitting energy.