Nomenclature of Coordination Compounds

The nomenclature of coordination compounds is a systematic way of naming complexes based on IUPAC rules. These rules ensure consistency and clarity in naming coordination chemistry structures worldwide.

Table of Contents

• Basic Rules
• Examples
• Special Notes
• Quiz
• MCQs
• FAQs

Basic Rules for Naming Coordination Compounds

1. Name the ligands first: Alphabetical order, regardless of charge.
2. Ligand names:
   • Neutral ligands: ammine (NH₃), carbonyl (CO), aqua (H₂O)
   • Anionic ligands: chloride → chloro, hydroxide → hydroxo, cyanide → cyano
   • Polydentate: en (ethylenediamine), ox (oxalate)
3. Number of ligands: mono-, di-, tri-, tetra-, penta-, hexa-. For complex ligands → bis-, tris-, tetrakis-.
4. Name the central metal: – For cationic/neutral → cobalt, iron. – For anionic → ferrate, cuprate.
5. Oxidation state: Shown in Roman numerals (III, II, IV).
6. Ionic compounds: Name cation first, then anion.

Examples

• [Co(NH₃)₆]Cl₃ → Hexaamminecobalt(III) chloride
• [Fe(CN)₆]⁴⁻ → Hexacyanoferrate(II) ion
• [Cu(H₂O)₄Cl₂] → Tetraaquadichlorocuprate(II)
• [PtCl₂(NH₃)₂] → Diamminedichloroplatinum(II)
• [Cr(en)₂(H₂O)₂]Cl₃ → Diethylenediaminediaquachromium(III) chloride

Special Notes

• Name ligands alphabetically (ignoring prefixes).
• Use bis-, tris-, tetrakis- for polydentate ligands.
• Anionic complexes → use suffix “-ate” (sometimes with Latin root: ferrum → ferrate).

Quiz: Test Your Understanding

1. [Ni(CO)₄] → Tetracarbonylnickel(0)
2. [Cr(H₂O)₆]Cl₃ → Hexaaquachromium(III) chloride
3. Anionic complexes → metal ends in “-ate”.
4. [Cu(en)₂Cl₂] → Bis(ethylenediamine)dichlorocopper(II)
5. Two ethylenediamine ligands → Prefix “bis-”.

(MCQs)

1. Suffix for metals in anionic complex?
   a) -ium
   b) -ate ✅
   c) -ide
   d) -ous
2. [Co(NH₃)₅Cl]²⁺ is named as:
   a) Pentaamminochlorocobalt(II)
   b) Pentaamminechlorocobalt(III) ✅
   c) Pentaminechlorocobalt(III)
   d) Pentamminochlorocobalt(III)
3. Ligand named “aqua”?
   a) NH₃
   b) H₂O ✅
   c) CO
   d) CN⁻
4. Prefix for three ligands?
   a) Tri-
   b) Tetra-
   c) Tris- ✅
   d) Bis-
5. Oxidation state in [Fe(CN)₆]⁴⁻?
   a) +2 ✅
   b) +3
   c) +4
   d) +6

(FAQs)

Q1: What are neutral ligands called?
A: Neutral ligands retain their molecule names, e.g., NH₃ → ammine, H₂O → aqua.

Q2: How do we name anionic complexes?
A: Metals in anionic complexes end with “-ate”, e.g., [Fe(CN)₆]⁴⁻ → Hexacyanoferrate(II).

Q3: What is the role of oxidation states in nomenclature?
A: Oxidation states are shown in Roman numerals after the metal name.