Explain `[Fe(H_2O)_6]^(3+)` is paramagnetic.

Explanation

In this case also, iron is in +3 oxidation state and has the electronic configuration as `3d^5`. This complex has been found to be paramagnetic due to the presence of five unpaired electrons. To account for this, the electrons in 3d-orbitals are not disturbed and the outer 4d-orbitals are used for hybridisation. The six orbitals (one 4s, three 4p and two 4d) are hybridised resulting `sp^3 d^2`-hybridisation. Six pairs of electrons, one from each water molecule occupy the six hybrid orbitals. The molecule is octahedral and is paramagnetic.

Since `[Fe(H_2O)_6]^(3+)` uses outer orbital (4d) in hybridisation, it is therefore, called outer orbital or high spin or spin free complex.