Why does crystal field splitting favours the formation of octahedral complex?
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The degenerate d-orbitals (in a spherical fieldenvironment) split into two levels i.e., e g and t 2g in the presence of ligands. The splittingof the degenerate levels due to the presence of ligands is called thecrystal-field splitting while the energy difference between the twolevels (e g and t 2g) is called thecrystal-field splitting energy. It is denoted by Δo.

Consider the complex Potassium hexacyanoferrate(II) whose chemical formula is K4[Fe(CN)6]. Now in this molecule the anion is a complex species with an overall charge of -4 ([Fe(CN)6]4-). Thus iron in this complex carries a charge of +2. Here the Fe+2 ion is surrounded by six cyanide ions. The electronic configuration of Fe is 4s23d6, therefore the electronic configuration of Fe+2 ion will be 3d6. In the absence of ligands, all the 5 d orbitals in Fe+2 ion are degenerate. However, when the ligands approach the central metal ion, the energy of all the d-orbitals is raised. These 5 d-orbitals are then split in two sets of t2g and Eg set. As CN is a strong ligand, it causes the pairing of electrons. So all the t2g orbitals are occupied with electrons.


Consider the complex Potassium hexacyanoferrate(II) whose chemical formula is K4[Fe(CN)6]. Now in this molecule the anion is a complex species with an overall charge of -4 ([Fe(CN)6]4-). Thus iron in this complex carries a charge of +2. Here the Fe+2 ion is surrounded by six cyanide ions. The electronic configuration of Fe is 4s23d6, therefore the electronic configuration of Fe+2 ion will be 3d6. In the absence of ligands, all the 5 d orbitals in Fe+2 ion are degenerate. However, when the ligands approach the central metal ion, the energy of all the d-orbitals is raised. These 5 d-orbitals are then split in two sets of t2g and Eg set. As CN is a strong ligand, it causes the pairing of electrons. So all the t2g orbitals are occupied with electrons.

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