Chemistry · Ch 5 — Coordination Chemistry
Ionisation Isomers
Ionisation Isomers
Ionisation isomers arise when an ionisable counter ion (a simple ion sitting outside the coordination sphere) is itself capable of acting as a ligand; exchanging that counter ion with one or more ligands already inside the coordination entity produces a different isomer, and the two isomers give DIFFERENT ions when dissolved in water. For example, in [Pt(en)₂Cl₂]Br₂ both Br⁻ and Cl⁻ can act as ligands, and swapping them gives the ionisation isomer [Pt(en)₂Br₂]Cl₂ -- the first compound releases Br⁻ ions in solution while the second releases Cl⁻ ions. Further examples given a …
Worked out. A self-check problem: a solution of [Co(NH₃)₄I₂]Cl treated with AgNO₃ gives a white precipitate (confirming the free, ionisable counter ion is Cl⁻, since AgCl is white). The student must give the formula of the isomer of the dissolved complex that instead gives a YELLOW precipitate with AgNO₃ (AgI is characteristically yellow) -- meaning iodide, not chloride, must be the free counter ion this time: [Co(NH₃)₄ICl]I. These two compounds, which exchange a coordinated iodide for the outer-sphere chloride, are called ionisation is …