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Unit 16

Coordination chemistry

Ammonia turns copper sulfate deep blue, haemoglobin holds oxygen on iron, cisplatin kills cancer cells and EDTA measures water hardness — all through complexes of metal ions with ligands. Starting from Werner’s coordination theory, this unit shows how to name complexes and count their isomers, explains their magnetism and colours with crystal-field theory, and measures how stable they are with formation constants and the chelate effect.

11 lessons ≈ 345 min 0 of 11 lessons complete

  1. 1 Complexes and ligands Why can silver ions precipitate only two of the chlorides in CoCl₃·5NH₃? Werner’s answer founded coordination chemistry: central ion, ligands, coordination number and a naming system. 25 min
  2. 2 Geometry and isomerism Cisplatin treats cancer while transplatin does not; [Co(en)₃]³⁺ comes in left- and right-handed forms. Turn the 3D models and count how many isomers a complex really has. 30 min
  3. 3 Crystal-field theory: splitting the d orbitals Once ligands approach, the five d orbitals are no longer equal. The contest between the splitting Δ and the pairing energy P decides high or low spin — and the magnetism. 35 min
  4. 4 Magnetism: counting unpaired electrons with a balance Iron(II) sulfate is pulled into a magnetic field; potassium ferrocyanide is not. Test Curie’s law on Curie’s own 1895 measurements of oxygen and ferrous sulfate, compute effective moments, and weigh the difference between high and low spin on a Gouy balance. 30 min
  5. 5 Symmetry, distortion and the Jahn–Teller effect The octahedra in CuF₂ are stretched; those in NiF₂ are almost regular. The character table tells how the d orbitals group in any geometry, and the Jahn–Teller theorem predicts which ions stretch their own octahedra. 35 min
  6. 6 Colour and the spectrochemical series Nickel(II) is green in water, blue-violet with ammonia and violet with ethylenediamine. The absorption band sits at Δo, and changing the ligand moves the colour along the spectrochemical series. 30 min
  7. 7 Electronic spectra: Δo and B from the bands [Cr(H₂O)₆]³⁺ has one Δo but two bands. Repulsion between the electrons pulls them apart; a Tanabe–Sugano diagram yields Δo and the Racah parameter B together, and six chromium(III) complexes give the nephelauxetic series. 35 min
  8. 8 Stability and the chelate effect Formation constants measure how stable a complex is. Why does one ethylenediamine hold on far better than two ammonias? The answer lies in entropy — and EDTA takes it to the limit. 30 min
  9. 9 Hard and soft acids and bases Aluminium occurs as oxides, mercury as sulfides; Fe³⁺ likes F⁻ best and Hg²⁺ likes I⁻. The ladder of halide stability constants and the absolute hardness computed from ionisation energies turn “hard likes hard, soft likes soft” into numbers you can check. 25 min
  10. 10 Ligand substitution: labile and inert A water molecule on copper(II) is gone within a nanosecond; on chromium(III) it waits three days, on iridium(III) two centuries. Charge, d electrons and the ligand-field activation energy set the pace, and the trans effect decides which ligand leaves a square-planar platinum complex first — which is how cisplatin is made. 35 min
  11. 11 Metal carbonyls and the 18-electron rule Why does a neutral nickel atom hold exactly four neutral CO molecules? Count valence electrons, see how σ donation and π back-donation leave a fingerprint in the infrared, and tell isomers apart by counting bands. 35 min