The energy of the d x2-y2 and d z2 orbitals (called e g orbitals) will be raised and that of the d xy, d yz and d xz orbitals (called t2g orbitals) will be lowered.
The repulsion between the electrons in metal d orbitals and the electrons (or negative charges) of the ligands is greater for the d x2-y2 and d z2 orbitals, which are pointing towards the axes, than the d xy, d yz and d xz orbitals, which are directed between the axes.
The ‘t2’ orbitals lie closer to the ligands than the ‘e’ orbitals, resulting in the energy of the ‘t2’ orbitals increasing and that of ‘e’ orbitals decreasing.
For d4 ions, two possible patterns of electron distribution arise: the fourth electron could either enter the t2g level and pair with an existing electron, or it could enter into the e g level.
The d x2-y2 and d z2 orbitals (called e orbitals) point towards the centre of each faces of the cube and the d xy, d yz and d xz orbitals (called t2 orbitals) point towards the edge centre of the cube.
If Δo < P, the fourth electron enters one of the e g orbitals giving the configuration t2g3 eg1, ligands for which Δo < P are known as weak field ligands and form high spin complexes.
If Δo > P, the fourth electron occupies a t2g orbital with configuration t2g4 eg0, ligands for which Δo > P are known as strong field ligands and form low spin complexes.
The oxidation number of the central atom in a complex is defined as the residual charge on it, if all the ligands are removed along with their electron pairs that are shared with the central atom.
Ligands are also classified as Ambidentate ligands which contain more than one donor atoms and can coordinate to the central atom through two different atoms, such as NO 2 – , CN – , SCN – , CNO – etc.
In the complex ions, [Fe(C 2 O 4 ) 3 ] 3 – and [Co(en) 3 ] 3+, the co-ordination number of both Fe and Co, is 6 because C 2 O 4 2 – and en (ethane - 1,2 - diamine) are bidentate ligands.
Chelating Ligands are di- or polydentate ligands that can bind to the central atom through two or more donor atoms and form ring complexes, such complexes are called chelates and these types of ligands are said to be chelating ligands.