Coordination Compounds Part 4

Concept:In tetrahedral complexes, the crystal field splitting energy ($\Delta_t$) depends directly on the ligand field strength of the attached ligands, following the spectrochemical series.Chemical Equation / Formula:Spectrochemical series (partial): $\mathrm{I}^- < \mathrm{Br}^- < \mathrm{Cl}^- < \mathrm{F}^-$.For tetrahedral $d^7$ Co(II) complexes, $\Delta_t$ is smaller than octahedral but maintains the same ligand order.Explanation:Statement I: Chloride ($\mathrm{Cl}^-$) is a stronger ligand than bromide ($\mathrm{Br}^-$).Hence $\Delta_t$ for $[\mathrm{CoCl}_4]^{2-}$ is greater than for $[\mathrm{CoBr}_4]^{2-}$.Energy of absorbed light is directly proportional to $\Delta_t$.Thus $[\mathrm{CoBr}_4]^{2-}$ absorbs light of lower energy.Statement I is true.Statement II: Iodide ($\mathrm{I}^-$) is a weaker ligand than chloride ($\mathrm{Cl}^-$).Therefore $\Delta_t$ for $[\mathrm{CoI}_4]^{2-}$ is smaller than for $[\mathrm{CoCl}_4]^{2-}$.The energy separation between d-orbitals is less, not more.Statement II is false.Answer:Option D: Statement I is true but Statement II is false.