IUPAC Naming in 5 Steps
Name the cation first, then the anion (like ionic compounds).
Within the complex, name ligands alphabetically before the central metal ion.
Use di-, tri-, tetra- for simple ligands; bis-, tris-, tetrakis- for complex ligands like en (ethylenediamine).
State the oxidation number of the central metal in Roman numerals in parentheses.
If the complex is an anion, add the suffix -ate to the metal name (e.g. ferrate, cuprate, platinate).
Crystal Field Theory (CFT) — Colour Logic
Ligands approach the central metal and split the 5 d-orbitals into two groups. The energy gap is Δ (Crystal Field Splitting Energy).
Strong Field Ligands (large Δ)
CO, CN⁻, NO₂⁻, en, EDTA. Force electron pairing → low spin complexes. Absorb low-energy visible light.
Weak Field Ligands (small Δ)
I⁻, Br⁻, Cl⁻, F⁻, OH⁻, H₂O. Don't force pairing → high spin complexes. Absorb high-energy visible light.
Isomerism in Coordination Compounds
| Type | Description | Example |
|---|---|---|
| Geometrical | cis-trans isomers; square planar or octahedral | Pt(NH₃)₂Cl₂ |
| Optical | Non-superimposable mirror images (chiral) | [Co(en)₃]³⁺ |
| Ionisation | Different ions in/out of coordination sphere | [CoBr(SO₄)(NH₃)₅] vs [Co(SO₄)(NH₃)₅]Br |
| Linkage | Ambidentate ligand bonded through different atoms | NO₂⁻ via N (nitro) vs O (nitrito) |
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