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IUPAC Nomenclature of Coordination Compounds | chemca

IUPAC Nomenclature of Coordination Compounds | chemca
Coordination Chemistry

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

The name of the metal depends on the charge of the complex ion (the coordination sphere).

Case 1: Cationic or Neutral Complex

The metal retains its standard English name.

  • $Fe$: Iron
  • $Ag$: Silver
  • $Cu$: Copper
  • $Pb$: Lead
Case 2: Anionic Complex

The metal name ends in -ate. Often uses Latin root.

  • $Fe$: Ferrate
  • $Ag$: Argentate
  • $Cu$: Cuprate
  • $Au$: Aurate
  • $Sn$: Stannate
  • $Co$: Cobaltate

4. Examples

1. $K_4[Fe(CN)_6]$
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
3. $[Pt(NH_3)_2Cl(NO_2)]$
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.

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