Nomenclature of Coordination Compounds

The rules for naming coordination compounds as recommended by IUPAC.

1. The cation is named before the anion, as in other ionic compounds. The rule holds regardless of whether the complex ion bears a net positive or a negative charge. For example, in K3[Fe(CN)6] and [Co(NH3)4Cl2]Cl compound, name the K+ and [Co(NH3)4Cl2]+ first, respectively.

2. Within a complex, ligands are named first, in alphabetical order, and the metal ion is named last.

3. The name of anionic ligand ends with the letter "O", whereas a neutral ligand is usually called by the name of the molecule. The exceptions are H2O (aqua), CO (carbonyl) and NH3 (ammine).

4. When several ligands of a particular kind are present, use the Greek prefix di, tri, tetra to name them. or example, the ligands in cation [Co(NH3)4Cl2]+ are named as tetraammine dichloro (prefixes are ignored when alphabetizing ligands). If the ligand itself contains a Greek prefix, we use the prefixes bis, tris and tetrakis to indicate the number of ligands present.

5. The oxidation number of the metal is written in roman numerals following the name of the metal. For example, the roman numeral III is used to indicate the +3 oxidation state of chromium in [Cr(NH3)4Cl2]+, which is named as tetraamminedichlorochromium (III) ion.

6. If the complex is an anion, its name ends in –ate.