Q.Which one of the following pairs represents linkage isomers?

Step 1. A linkage-isomer pair must share the SAME formula and differ only in which donor atom of an ambidentate ligand is bonded to the metal (Section 5.5.1.1).

Step 2. Option (a), [Cu(NH₃)₄][PtCl₄] and [Pt(NH₃)₄][CuCl₄], swaps entire ligand SETS between two different complex ions -- that is coordination isomerism (Section 5.5.1.2), not linkage isomerism.

Step 3. Option (c), [Co(NH₃)₄(NCS)₂]Cl and [Co(NH₃)₄(SCN)₂]Cl, is an unambiguous linkage-isomer pair: NCS⁻/SCN⁻ is the same thiocyanate ion written to show binding through nitrogen (isothiocyanato-N) versus through sulfur (thiocyanato-S), exactly the ambidentate-ligand pattern this chapter defines. …

Check each option for the linkage-isomerism signature -- identical formula, same ligand set, differing only in the donor atom of one ambidentate ligand -- and rule out any option that instead swaps ligands b …

• Picking option (a) because it also 'swaps something between two formulas' -- that is coordination isomerism (interchange between cation and anion complex ions), a different phenomenon from linkage isomerism. …