Coordination Compounds (Class 12): Naming & Isomerism Made Simple
The IUPAC naming rules and the main types of isomerism in coordination compounds — explained with quick examples.
Quick idea: Coordination compounds are named by listing ligands (alphabetically) before the metal, with the metal’s oxidation state in Roman numerals. Isomerism arises from different arrangements of the same atoms.
Naming rules (the essentials)
- Name ligands first, alphabetically, then the central metal.
- Use prefixes di, tri, tetra for simple ligands (bis, tris for complex ones).
- Anionic ligands end in ‑o (chloro, cyano); the metal in an anionic complex ends in ‑ate.
- Show the metal’s oxidation state in Roman numerals in brackets.
Example: K₄[Fe(CN)₆] = potassium hexacyanoferrate(II).
Main types of isomerism
| Type | What differs | Quick example |
|---|---|---|
| Ionisation | Ion released in solution | [Co(NH₃)₅Br]SO₄ vs [Co(NH₃)₅SO₄]Br |
| Linkage | Atom of ligand bonded | –NO₂ vs –ONO |
| Geometrical | Cis/trans arrangement | [Pt(NH₃)₂Cl₂] |
| Optical | Non-superimposable mirror images | [Co(en)₃]³⁺ |
How to answer board questions
- Identify the coordination sphere and counter ions.
- Determine the metal’s oxidation state before naming.
- For isomerism, ask “what exactly is being rearranged?”
FAQs
Which isomerism is asked most?
Geometrical and optical isomerism are common; ionisation and linkage also appear. Confirm emphasis from your syllabus.
Do I need crystal field theory too?
Basic CFT (colour, magnetic behaviour) is part of the chapter; naming and isomerism are the high-frequency scoring parts.
Find coordination chemistry tricky?
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