Naming metal complexes according to IUPAC rules follows a systematic approach. Here’s a clear, step-by-step explanation:
1. Identify the complex components
A metal complex usually consists of:
- Central metal atom or ion
- Ligands (molecules or ions attached to the metal)
Example: [Cu(NH3)4]SO4
- Metal: Cu²⁺
- Ligands: NH₃ (ammonia)
- Counter ion: SO₄²⁻
2. Name the ligands first
- Anionic ligands (negative charge) → add suffix “-o”
- Cl⁻ → chloro
- OH⁻ → hydroxo
- CN⁻ → cyano
- Neutral ligands → use normal name (usually in English)
- H₂O → aqua
- NH₃ → ammine
- CO → carbonyl
- If the ligand is complex or contains numbers, use prefixes to indicate quantity:
- mono- (1), di- (2), tri- (3), tetra- (4), penta- (5), hexa- (6)
- If ligand names are complex, use bis, tris, tetrakis, etc.
Example: [Cr(H2O)6]³⁺ → six water ligands → hexa-aqua
3. Name the central metal
- Name the metal after the ligands.
- Oxidation state of the metal is indicated in Roman numerals in parentheses.
- If the metal is anionic, its name ends with “-ate” (usually for anionic complexes).
Example: [Fe(CN)6]⁴⁻ → hexacyanoferrate(II)
4. Name the complex as a whole
- Combine ligand names (alphabetically) before the metal.
- Counter ions come after the complex.
Example 1: [Cu(NH3)4]SO4
- Ligand: NH₃ → ammine
- Number: 4 → tetraammine
- Metal: Cu²⁺ → copper(II)
- Counter ion: SO₄²⁻ → sulfate
- Full name: tetraamminecopper(II) sulfate
Example 2: [CoCl2(en)2]Cl
- Ligands: Cl⁻ → chloro, en → ethylenediamine (bidentate)
- Number: 2 for each → dichloro, bis(ethylenediamine)
- Metal: Co³⁺ → cobalt(III)
- Counter ion: Cl⁻ → chloride
- Full name: dichlorobis(ethylenediamine)cobalt(III) chloride
5. Special points
- Polydentate ligands (ligands that bind through more than one atom) have special names:
- ethylenediamine → en
- oxalate → ox²⁻
- Alphabetical order ignores numerical prefixes when ordering ligands.
- Neutral ligands like NH₃, H₂O, CO come before anionic ligands alphabetically if needed.
Summary Formula:
[prefix-ligand name(s) + metal name + (oxidation state)] + counter ion