IUPAC naming of complex compounds

IUPAC Naming of Complex Compounds

The naming of coordination compounds follows a set of standardized rules formulated by the International Union of Pure and Applied Chemistry (IUPAC) to ensure clarity and uniformity. These rules ensure consistency and clarity when identifying the structure and composition of coordination compounds.

General Rules for IUPAC Naming

1. Name the Ligands First: Ligands are named before the central metal atom/ion. If more than one type of ligand is present, they are named in alphabetical order, ignoring prefixes.
2. Use Prefixes for Multiple Ligands: Use prefixes like di-, tri-, tetra-, penta-, etc., to indicate the number of each type of ligand. For complex ligand names, use bis-, tris-, tetrakis-, etc.
3. Neutral Ligands: Certain neutral molecules, when acting as ligands, are assigned specific IUPAC-approved names:
   • H₂O → aqua
   • NH₃ → ammine
   • CO → carbonyl
   • NO → nitrosyl
4. Name the Central Metal Atom/Ion:
   • For neutral or positively charged complexes, the metal is named using its standard elemental name.
   • If the complex is anionic, the metal name ends in -ate and often uses its Latin name if available.
5. Oxidation State: The central metal's oxidation number is indicated in Roman numerals within parentheses, placed right after its name.
6. Name the Counter Ion Last: If the complex ion is part of a salt, name the cation first and the anion second (as in other ionic compounds).

Examples

• [Cr(NH₃)₆]Cl₃ → hexaamminechromium(III) chloride
• [PtCl₄]²⁻ → tetrachloridoplatinate(II) ion
• [Co(en)₂Cl₂]⁺ → bis(ethylenediamine)dichloridocobalt(III) ion
• K[Fe(CN)₆] → potassium hexacyanidoferrate(III)

Key Notes

• Ligand names are written without spaces, even if bis/tris/tetrakis are used.
• Alphabetical order of ligands is based on the ligand name (not prefix).
• Anionic ligands typically end in “-o” (e.g., chloro for Cl⁻, cyano for CN⁻).