Coordination Compounds: Naming, Geometry and Isomerism · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Naming complexes and spotting isomers

Science · Chemistry · ages 19-20
Name ______________________   Date ____________

  1. What is the coordination number of [Co(NH3)6]Cl3? Type the number.

    Answer: ______________

  2. When you name a complex ion, what comes first?

    • The metal with its oxidation state in roman numerals
    • The ligands in alphabetical order with their counts
    • The counter ions outside the brackets, then the rest

  3. What is the oxidation state of cobalt in [Co(NH3)4Cl2]Cl? Type the number without a plus sign, for example 2 for +2.

    Answer: ______________

  4. In a square planar complex, how do cis and trans isomers differ?

    • Cis puts matching ligands side by side and trans puts them opposite
    • Cis has two more ligands than trans, so its coordination number is higher
    • Cis is always the charged form and trans is always the neutral form

  5. What is the formula of hexaamminecobalt(III) chloride?

    • [Co(NH3)6]Cl3
    • [Co(NH3)3]Cl6
    • Co(NH3)6Cl

  6. An octahedral complex has three ligands of one kind and three of another. How do its fac and mer isomers differ?

    • Fac has three metal centres and mer has one, joined by bridges
    • Fac puts all three on one face; mer has two of them opposite
    • Fac puts the three matching ligands in one straight line through the metal

  7. Three bidentate ligands around a metal give a coordination number of three.

    Circle one:   True   False

  8. Two complexes differ only in which atom of one ligand binds the metal. Which isomerism is this?

    • Coordination isomerism
    • Ionisation isomerism
    • Linkage isomerism
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Naming complexes and spotting isomers W1-mt_rkHM3jL3Ri-s1

  1. 6 · Six ammonias each donate one atom, so the count is six.
  2. The ligands in alphabetical order with their counts · In a complex ion the ligands come first, in alphabetical order with their count prefixes, and the metal follows with its oxidation state.
  3. 3 · Inside the brackets the ammines give 0 and the two chlorido ligands give -2. The chloride outside gives -1. The total of -3 must be balanced, so cobalt is +3.
  4. Cis puts matching ligands side by side and trans puts them opposite · The two forms differ only in the relative positions of the matching pair.
  5. [Co(NH3)6]Cl3 · Hexa means six ammonias inside, and cobalt(III) needs three chlorides outside.
  6. Fac puts all three on one face; mer has two of them opposite · In fac, all three matching ligands share one triangular face, each 90 degrees from the other two. In mer, they lie in one plane through the metal, so two of them are opposite each other.
  7. False · Each bidentate ligand donates two atoms, so three give six.
  8. Linkage isomerism · A swapped donor atom with everything else fixed means linkage isomerism.
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