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IUPAC nomenclature of coordination compounds’ importance is that it helps to create uniformity and reduce confusion. A coordination compound has ligands, metal ions, and ions outside the coordination sphere to balance charge. All these entities have to be kept in mind while naming a coordination complex. Even the charge of the central metal ion has to be considered during its nomenclature.

For the accurate IUPAC nomenclature of coordination compounds, the chemical formula of the compound must be written accurately. The coordination sphere has to be enclosed in square brackets, and the charge on it must always be balanced.

The Formula of Coordination Compounds

A formula provides basic information about the compound, including which metal ion it has, its oxidation number of it, ligands present, etc. It is concise and clear.

In this IUPAC nomenclature of coordination notes, we exclusively cover mononuclear compounds. Mononuclear compounds are those that have only one metal ion in the coordination sphere. The following rules must be kept in mind while writing the formula of coordination compounds:

1. The coordination sphere must always be enclosed in square brackets.
2. The central metal ion is written first in the coordination sphere, which is followed by writing ligands in alphabetical order.
3. There should be no space between the metal and ligands.
4. If the ligand has multiple atoms like NH3, H2O, etc., they must be enclosed in parentheses.
5. The charge on the coordination sphere is written on the top right corner outside the coordination sphere when there are no ions to balance it.

For example, in K3[Fe(CN)6], the metal is written first in the coordination sphere. The multi-atom ligand is enclosed in round brackets and its number is written at the bottom. Now, there are three Potassium ions outside the coordination sphere to balance the -3 charge on the sphere.

In [Pt(NH3)2Cl2], the Platinum is written first. There are two ligands here – Ammonia and Chloride. Going alphabetically, Ammonia should be written first, and then Chloride. Ammonia is a multi-atom ligand, so it is enclosed in round brackets. The coordination sphere is neutral, so no charge would be mentioned on it.

To write the formula or IUPAC nomenclature of coordination compounds, one must know the charge on ligands and the oxidation state of metal.

The Naming of Ligands

Anionic ligands end with either ‘o’, ‘ito’, or ‘ato’, depending on their actual names.

• If the ion’s actual name ends in ‘ide’, like fluoride, oxide, then the ‘ide’ is replaced with ‘o’. For example, Fluoride becomes fluoro and oxide becomes oxo
• If the ion’s name ends in ‘ate’ like sulphate, then ‘ate’ is replaced with ‘ato’. Sulphate becomes Sulphato
• If the ion’s name ends in ‘ite’ like sulphite, then ‘ite’ is replaced with ‘ito’. Sulphite becomes Sulphito

Let’s go through the names of commonly used anionic ligands in coordination chemistry:

Let’s go through the names of commonly used neutral ligands in coordination chemistry:

IUPAC Nomenclature of Coordination Compounds

When the coordination sphere is anionic, it is balanced by cations outside. These cations are written first followed by the naming of the coordination sphere. The following rules must be followed:

1. The cation must always be written first (it could be the balancing ions or the coordination sphere).
2. Ligands are written first in alphabetical order, followed by the name of the central metal.
3. If the coordination sphere is anionic, we put ‘ate’ as the suffix of the metal. If the coordination sphere is cationic, the name of the metal is written as it is.
4. We use prefixes di, tri, tetra, etc., to indicate the number of ligands in the compound.
5. If the ligand already has any of these prefixes in the name, we use prefixes bis, tris, tetrakis, etc., to indicate the number of ligands in the compound.
6. The oxidation state of the metal is written in roman numerals in parentheses after its name.

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Conclusion 

The detailed IUPAC nomenclature of coordination compounds notes cover every aspect of writing the formula and name of coordination complexes. IUPAC nomenclature of coordination compounds importance is that it helps the name of coordination complex uniform everywhere. The name of the ligands and the charge on them must be known, to be able to name the compound properly. Ligand’s name is written in alphabetic order.

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