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Linkage, coordination, ionisation and solvate isomerism sheet
3-mark answer frame

Explain linkage, ionisation and coordination isomerism with one example each.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Open with a definition. Structural isomers have the same formula but different bonds between the metal and its ligands or counter ions.
  2. 2 · Linkage isomerism. An ambidentate ligand binds through different atoms: [Co(NH₃)₅(NO₂)]Cl₂ (N-bonded, yellow) and [Co(NH₃)₅(ONO)]Cl₂ (O-bonded, red).
  3. 3 · Ionisation isomerism. An ion inside swaps with the counter ion: [Co(NH₃)₅(SO₄)]Br and [Co(NH₃)₅Br]SO₄, which give Br⁻ and SO₄²⁻ in water respectively.
  4. 4 · Coordination isomerism. Ligands exchange between cationic and anionic complexes: [Co(NH₃)₆][Cr(CN)₆] and [Cr(NH₃)₆][Co(CN)₆].
  5. 5 · Close in one line. So all three pairs share a formula but differ in which atoms are bonded to each metal.

Scoring tip: For each type, write a pair of formulas, not just one. The mark is for showing what changes.