Once you can find the parts of a coordination compound, its name follows a fixed recipe. The name tells a chemist every ligand, the metal and its oxidation state.
Key idea
Why it works
| Ligand | Name | Ligand | Name |
|---|---|---|---|
| $\mathrm{NH_3}$ | ammine | $\mathrm{Cl^-}$ | chlorido (chloro) |
| $\mathrm{H_2O}$ | aqua | $\mathrm{CN^-}$ | cyanido (cyano) |
| $\mathrm{CO}$ | carbonyl | $\mathrm{OH^-}$ | hydroxido (hydroxo) |
| en | ethylenediamine | $\mathrm{C_2O_4^{2-}}$ | oxalato |
Worked examples
Worked example: A complex cation
- Complex cation $\mathrm{[Co(NH_3)_4Cl_2]^+}$; anion chloride. Cobalt: $x + 0 + 2(-1) = +1$, so Co(III).
- Ligands alphabetically: ammine (a) before chlorido (c): tetraammine, dichlorido.
- Name: tetraamminedichloridocobalt(III) chloride.
Answer: Tetraamminedichloridocobalt(III) chloride.
Worked example: A complex anion
- Cation: potassium. Complex anion $\mathrm{[Fe(CN)_6]^{3-}}$: $x + 6(-1) = -3$, so Fe(III).
- Six cyanido ligands: hexacyanido. Anion, so iron becomes ferrate.
- Name: potassium hexacyanidoferrate(III) (older: potassium hexacyanoferrate(III)).
Answer: Potassium hexacyanidoferrate(III).
Worked example: From name to formula
- Complex: Ag(I) with two $\mathrm{NH_3}$: $\mathrm{[Ag(NH_3)_2]^+}$.
- One nitrate balances it: $\mathrm{[Ag(NH_3)_2]NO_3}$.
Answer: $\mathrm{[Ag(NH_3)_2]NO_3}$.
Formulas follow their own order: inside the brackets, the metal comes first, then the ligands. Many books list neutral ligands before anionic ones, as in $\mathrm{[Co(NH_3)_4Cl_2]^+}$; current IUPAC rules list ligands alphabetically by their formulas. Either way, the brackets enclose the complex and its charge sits outside them.
Common mistake