How are octahedral complexes with high spin and low spin states formed ? What is the condition of their formation ?

Explanation

There are three `t_(2g)` orbitals with lower energy and two `e_(g)` orbitals with higher energy. Three electrons with parallel spins can first enter into the lower energy three `t_(2g)` orbitals, i.e., for complexes with `d^(1), d^(2)` and `d^(3)` ion. For `d^(4), d^(5), d^(6)` etc. ions, the electrons can either into `t_(2g)` orbitals and pair up or they may enter into `e_(g)` orbitals. The former gives rise to low spin complex while the latter gives rise to high spin complex.
If cystal field splitting energy (difference of energy between `t_(2g)` and `e_(g)` orbitals) is large, low spin state is more stable and if it is small, high spin state is more stable.