(a) IUPAC Nomenclature of Coordination Compounds

Step 1 (Oxidation State Calculation): [0.5 Mark]

• For (i) $[\text{Ag}(\text{NH}_3)_2] [\text{Ag}(\text{CN})_2]$: Let the oxidation state of Ag be $x$. Since $\text{NH}_3$ is neutral (0) and $\text{CN}^-$ is -1: $$x + 2(0) + x + 2(-1) = 0 \implies 2x = 2 \implies x = +1$$
• For (ii) $\text{K}_3[\text{Fe}(\text{C}_2\text{O}_4)_3]$: Let the oxidation state of Fe be $x$. $\text{K} = +1$, $\text{C}_2\text{O}_4^{2-} = -2$: $$3(+1) + x + 3(-2) = 0 \implies 3 + x - 6 = 0 \implies x = +3$$

Step 2 (IUPAC Naming Rules Application): [0.5 Mark]

Apply the rule: [Cation] then [Anion]. For complex ions, name ligands alphabetically followed by the metal name (use suffix '-ate' for anionic complexes).

Step 3 (Final Concluded Answer): [1.0 Mark]

• (i) diamminesilver(I) dicyanoargentate(I)
• (ii) potassium trioxalatoferrate(III)

(b) Ionisation Isomerism and Chelate Effect

Step 1 (Chemical Test for Ionisation Isomers): [1.0 Mark]

• Principle: Ionisation isomers give different ions in solution.
• Test: Add $\text{AgNO}_3$ solution to the aqueous solution of the complexes.
  • $[\text{Co}(\text{NH}_3)_5\text{SO}_4]\text{Cl}$ gives a white precipitate of $\text{AgCl}$.
  • $[\text{Co}(\text{NH}_3)_5\text{Cl}]\text{SO}_4$ gives no precipitate with $\text{AgNO}_3$ (but gives a white precipitate with $\text{BaCl}_2$ due to $\text{SO}_4^{2-}$ ions).

Step 2 (Definition of Chelate Effect): [0.5 Mark]

When a di- or polydentate ligand uses its two or more donor atoms to bind to a single metal ion, it forms a ring-like structure known as a chelate ring. This results in higher stability of the complex compared to similar complexes with monodentate ligands; this is called the Chelate Effect.

Step 3 (Example): [0.5 Mark]

Formation of tris(ethane-1,2-diamine)cobalt(III) ion: $$[\text{Co}(\text{H}_2\text{O})_6]^{3+} + 3\text{en} \rightarrow [\text{Co}(\text{en})_3]^{3+} + 6\text{H}_2\text{O}$$

💡 EL10 Concept Insight:

Think of the Chelate Effect like holding hands: if a ligand holds onto the metal with two "hands" (donor atoms)