$\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ and $\left[\mathrm{CoF}_6\right]^{3-}$ are respectively known as :

$\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ <br/><br/>$\mathrm{Co}^{3+}($ strong field ligand $) \Rightarrow 3 \mathrm{~d}^6\left(\mathrm{t}_{2 \mathrm{~g}}^6, \mathrm{e}_{\mathrm{g}}^0\right)$, <br/><br/>Hybridisation : $\mathrm{d}^2 \mathrm{sp}^3$ <br/><br/>Inner obital complex(spin paired complex) <br/><br/>Pairing will take place. <br/><br/>$\left[\mathrm{CoF}_6\right]^{3-}$ <br/><br/>$\mathrm{Co}^{3+}($ weak field ligand $) \Rightarrow 3 \mathrm{~d}^6\left(\mathrm{t}_{2 \mathrm{~g}}^4, \mathrm{e}_{\mathrm{g}}^2\right)$ <br/><br/>Hybridisation : $\mathrm{sp}^3 \mathrm{~d}^2$ <br/><br/>Outer orbital complex (spin free complex) <br/><br/>No pairing will take place