`[Fe(H_2O)_6]^(3+)` is strongly paramagnetic whereas `[Fe(CN)_6]^(3-)` is weakly paramagnetic. Explain.

Explanation

In presence of `CN^(ɵ)` (a strong ligand) the 3d electrons pair up leaving only one unpaired electron. The hydridisation is `d^(2)sp^(3)` forming inner orbital complex. In the presence of `H_2O` (a weak ligand), `3d` electrons do not pair up. The hydridisation is `sp^(3)d^(2)` forming an outer orbital complex containing five unpaired electrons, it is strongly paramagnetic.