Chemistry - Coordination Chemistry Question with Solution | TestHub

Key Idea: The magnitude of ${\Delta }_{\propto \mathrm{c}t}$ (the orbital splitting energy) is decided by the nature of ligand Strong field ligand has highest ${\Delta }_{\text{oct }}$. The increasing field strength is as ${\mathrm{I}}^{-}<{\mathrm{Br}}^{-}<{\mathrm{Cl}}^{-}<{\mathrm{F}}^{-}<{\mathrm{OH}}^{-}<{\mathrm{H}}_2\mathrm{O}<{\mathrm{C}}_2{\mathrm{O}}_4^{2-}<{\mathrm{NH}}_3<\mathrm{en}<{\mathrm{NO}}_2^{-}<{\mathrm{CN}}^{-}$ The ${\mathrm{CN}}^{-}$is the strongest ligand among these, hence the magnitude of ${\Delta }_{\text{oct }}$ will be maximum in ${\left[\mathrm{Co}(\mathrm{CN}{)}_6\right]}^{3-}$. Note : The magnitude of ${\Delta }_{\text{oct }}$ is also decided by oxidation state of the metal ion. Thus, greater the ionic charge on the central metal ion, the greater the value of ${\Delta }_{\text{oct }}$. But here the oxidatinon state of Co metal ion is same in all complexes.