How tetrahedral complex splitting takes place?, Chemistry

The tetrahedral arrangement of four ligands surrounding the metal ion may be visualized. It is clear that in tetrahedral field, none of the orbitals point exactly towards the ligands and therefore, the splitting of energy will be less that in octahedral field. The tree d-orbitals dxyand dyz and dzx are pointing close to the direction in which the ligands are approaching while the two orbitals  244_Untitled.png  and  942_Untitled.png  are lying in between the ligands. Therefore, the energies of the three orbitals will be raised while the energies of the two orbitals will be lowered. Thus, in the presence of octahedral field, the degeneracy of five d-orbitals splitting as:
    
The two orbitals,  244_Untitled.png  and  942_Untitled.png  becomes stable and their energies are lowered. These are designated as 'e' orbitals.
    
The three orbitals, dxy, dyz and dzx become unstable and their energies are raised. These are designated as 't2' orbitals. 

The magnitude of crystal field splitting is the difference between e and t2 orbitals and is designated as Δt, (the subscript indicating tetrahedral complexes). It is also measured in terms of Dq and Δt, = 10 Dq. If we compare the magnitude of crystal field splitting in octahedral and tetrahedral complexes (having same metal ion, ligands and metal ion-ligand distances), it has been observed that the crystal field splitting in octahedral complexes t) is considerably less than in octahedral complexes 0). It has been found to be Δt = 4/9 Δ0.

There are two main reasons for the smaller value of crystal field splitting in tetrahedral than in octahedral complexes.
    
In tetrahedral complexes there are four ligands while there are six ligands in octahedral complexes. Therefore, lesser ligands produce less crystal field splitting. The crystal field splitting in tetrahedral field is about two third of the octahedral field.
    
In tetrahedral field, none of the orbitals is pointing directly towards the ligands and, therefore, splitting is less.

Since the magnitude of crystal field splitting in tetrahedral field is quite small and is always less the pairing energy, therefore, the pairing of electrons will never be energetically favourable. Thus; all the tetrahedral complexes are high spin complexes. No tetrahedral complex with low spin has been found to exist. 

 

 

 

Posted Date: 6/25/2012 7:00:11 AM | Location : United States







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