Coordination Compounds Part 2

Spin only magnetic moment, $\mu = \sqrt{n(n+2)} \text{ BM}$ where, $n =$ number of unpaired electrons and $\mu \propto n$. (i) $[\mathrm{FeF}_6]^{3-} \Rightarrow \mathrm{Fe}^{3+} = (3d^{5}) + 6 \times \mathrm{F}^{-}$(weak field ligand). Thus, pairing of electron does not take place.(ii) $[\mathrm{Co}(\mathrm{NH}_3)_6]^{3+} \Rightarrow \mathrm{Co}^{3+} = (3d^{6}) + 6 \times \mathrm{NH}_3$ (strong field ligand). Thus, pairing of electron takes place.(iii) $[\mathrm{NiCl}_4]^{2-} \Rightarrow \mathrm{Ni}^{2+} = (3d^{8}) + 4 \times \mathrm{Cl}^{-}$(weak field ligand). Thus, pairing of electron takes place.(iv) $[\mathrm{Cu}(\mathrm{NH}_3)_4]^{2+} \Rightarrow \mathrm{Cu}^{2+}(3d^{9}) + 4 \times \mathrm{NH}_3$ (strong field ligand). Thus, pairing of electron takes place.So, the decreasing order of $\mu$ is $\mu_{i_{(n=5)}} > \mu_{iii_{(n=2)}} > \mu_{iv_{(n=1)}} > \mu_{ii_{(n=0)}}$