IUPAC Naming of Coordination Compounds
IUPAC nomenclature of coordination compounds follows a fixed order: name the cation before the anion, name ligands alphabetically before the metal within the coordination entity, and write the oxidation state of the metal in Roman numerals.
In one line: Name outside charge partners first, then name the bracket from ligand alphabet to metal Roman numeral.
Practice This ConceptUnderstand it
- Ligands have special names such as ammine for NH3, aqua for H2O, chloro for Cl-, hydroxo for OH-, cyano for CN-, and nitro or nitrito depending on the donor atom.
- Prefixes such as di, tri, tetra, penta, and hexa show the number of identical ligands.
- Alphabetical order is decided by ligand names, not by numerical prefixes.
- If the complex ion is anionic, the metal name usually ends in -ate, such as ferrate, cuprate, cobaltate, or platinate.
Example
Rule to remember
Naming order rule: cation first, anion second.
Inside coordination entity: ligand names in alphabetical order followed by metal name and oxidation state in Roman numerals.
For an anionic complex, use the metal name with -ate ending where applicable.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
Name K4[Fe(CN)6].
- 1Potassium is the cation.
- 2In [Fe(CN)6]4-, each CN- is -1, so x - 6 = -4 and x = +2.
- 3Six cyano ligands give hexacyano.
- 4Since the complex ion is anionic, iron becomes ferrate.
- 5Name: potassium hexacyanoferrate(II).
Method you can reuse
- 1Identify cation and anion.
- 2Isolate the coordination entity.
- 3Calculate metal oxidation state.
- 4Convert ligand formulae into ligand names.
- 5Arrange ligand names alphabetically.
- 6Add metal name with Roman numeral, then name counter ions.
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
Name the ligand H2O and the ligand NH3 in coordination compound nomenclature.
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Common wrong answer
A common wrong answer for K4[Fe(CN)6] is potassium hexacyanoiron(II), missing the anionic complex ending ferrate.
Don't mix this up
Exam tip
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
- 1
Enough for 1 mark
IUPAC nomenclature of coordination compounds follows a fixed order: name the cation before the anion, name ligands alphabetically before the metal within the coordination entity, and write the oxidation state of the metal in Roman numerals.
- 2
Add for 2 marks
Example: [Co(NH3)5Cl]Cl2 is named pentaamminechlorocobalt(III) chloride. The complex ion is cationic, NH3 is named ammine, Cl- inside the sphere is named chloro, and cobalt has oxidation state +3.
- 3
Add for 3 marks
Ligands have special names such as ammine for NH3, aqua for H2O, chloro for Cl-, hydroxo for OH-, cyano for CN-, and nitro or nitrito depending on the donor atom.
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