Electron configuration in complexes
The rules for deducing the orbital occupancy for the eg and t2g orbitals are the same as for other orbitals.
However, for metal ions having more than three d-electrons, the number of unpaired electrons may depend on the size of Δo. This is because Δo is of the same order as the energy increase due to electron pairing in the same orbital.
Because Δo depends on both the metal ion and the ligand, the number of unpaired electrons also may vary with the metal ion and the ligand.
| eg t2g |  |  Δo |
| |
- A maximum of two electrons can occupy each orbital.
- Orbitals of equal energy are occupied singly before a second electron enters any of them.
However, for metal ions having more than three d-electrons, the number of unpaired electrons may depend on the size of Δo. This is because Δo is of the same order as the energy increase due to electron pairing in the same orbital.
- if Δ0 is small as in complexes having weak field ligands, the fourth, and fifth electrons occupy singly the e2g orbitals. The sixth electron pairs with an electron in a t2g orbital.
- if Δ o is large as in complexes having strong field ligands, pairing occurs in the t2g orbitals before any electrons are placed in the eg orbitals.
Because Δo depends on both the metal ion and the ligand, the number of unpaired electrons also may vary with the metal ion and the ligand.