IUPAC Nomenclature
Rules for naming Coordination Compounds: Ligands, Metals, and Oxidation States.
By chemca Team • Updated Jan 2026
Naming coordination compounds requires a specific set of rules defined by IUPAC. The name generally consists of the cation followed by the anion, similar to simple salts.
1. Basic Order of Naming
- Cation First: The cation is named first in both positively and negatively charged coordination entities.
- Coordination Sphere: Within the square brackets, ligands are named first (in alphabetical order), followed by the central metal atom/ion.
- Oxidation State: The oxidation number of the metal is written in Roman numerals in parentheses immediately after the metal name.
2. Naming Ligands
A. Anionic Ligands
Names end in -o (usually replacing -ide with -ido, -ate with -ato, -ite with -ito).
| $Cl^-$ | Chlorido | $CN^-$ | Cyanido |
| $Br^-$ | Bromido | $OH^-$ | Hydroxido |
| $SO_4^{2-}$ | Sulphato | $C_2O_4^{2-}$ (ox) | Oxalato |
| $NO_2^-$ | Nitrito-N | $ONO^-$ | Nitrito-O |
B. Neutral Ligands
Retain their original names, with specific exceptions.
- $H_2O$: Aqua
- $NH_3$: Ammine (Note the double 'm')
- $CO$: Carbonyl
- $NO$: Nitrosyl
- $en$ ($H_2NCH_2CH_2NH_2$): Ethane-1,2-diamine
C. Prefixes for Number
Use di, tri, tetra, penta, hexa for simple ligands.
Use bis, tris, tetrakis if the ligand name already contains a numerical prefix (e.g., ethylenediamine, triphenylphosphine) or is polydentate.
Example: $[Co(en)_3]^{3+}$ is Tris(ethane-1,2-diamine)cobalt(III).
3. Naming the Central Metal
4. Examples
1. $K_4[Fe(CN)_6]$
Cation: Potassium
Complex Anion: Hexacyanidoferrate(II)
Name: Potassium hexacyanidoferrate(II)
Cation: Potassium
Complex Anion: Hexacyanidoferrate(II)
Name: Potassium hexacyanidoferrate(II)
2. $[Co(NH_3)_6]Cl_3$
Complex Cation: Hexamminecobalt(III)
Anion: Chloride
Name: Hexamminecobalt(III) chloride
Complex Cation: Hexamminecobalt(III)
Anion: Chloride
Name: Hexamminecobalt(III) chloride
3. $[Pt(NH_3)_2Cl(NO_2)]$
Ligands: Ammine (A), Chlorido (C), Nitrito-N (N). Alphabetical: A, C, N.
Name: Diamminechloridonitrito-N-platinum(II)
Ligands: Ammine (A), Chlorido (C), Nitrito-N (N). Alphabetical: A, C, N.
Name: Diamminechloridonitrito-N-platinum(II)
Bridging Ligands: If a ligand connects two metal centers, use the prefix $\mu$- before its name.
Example: $[(NH_3)_5Cr-OH-Cr(NH_3)_5]^{5+}$
Name: $\mu$-hydroxidobis(pentamminechromium(III)) ion.
Example: $[(NH_3)_5Cr-OH-Cr(NH_3)_5]^{5+}$
Name: $\mu$-hydroxidobis(pentamminechromium(III)) ion.
Knowledge Check
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