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Tamil Nadu Board of Secondary EducationHSC Science Class 12

Nomenclature of Coordination Compounds

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Estimated time: 8 minutes
CBSE: Class 12

Key Points: Nomenclature of Coordination Compounds

Rules for Writing Formulae:

  • The cation is written first, then the anion.
  • In the formula of the complex ion/entity, the central metal atom is written first, then the ligands in alphabetical order.
  • The formula of the entire coordination entity is enclosed in square brackets.

Rules for Naming:

Rule 1: Names of neutral coordination complexes are given without spaces. Cation is named first, separated by a space from the anion.

Rule 2 (Naming ligands first):

  • Ligands that act as anions end in –o: Cl⁻ = chlorido, Br⁻ = bromido, I⁻ = iodido
  • Anions ending in –ite and –ate are replaced with –ito and –ato: SO₄²⁻ = sulphato, CO₃²⁻ = carbonato, NO₂⁻ = nitrito, CH₃COO⁻ = acetato
  • Neutral ligands get the same name as the uncoordinated molecule (with spaces omitted): C₅H₅N = pyridine, (CH₃)₂SO = dimethylsulfoxide (DMSO)

Exceptions — neutral ligands with special names:

Molecule Special Name
H₂O aqua
NH₃ ammine
CS thiocarbonyl
CO carbonyl
NO nitrosyl

Rule 3 (Prefixes): Greek prefixes (di, tri, tetra) are used for simple ligand names. For polydentate ligands (i.e., those with a binding site name containing di/tri already): bis-, tris-, tetrakis-, pentakis-, hexakis- are used instead. e.g., bis(ethane-1,2-diamine) not "diethylenediamine".

Rule 4: Oxidation state of the metal is indicated by a Roman numeral in parentheses after the metal name. NO = nitrosyl.

Rule 5 (Complex ion is a cation): Metal is named same as the element. e.g., Co in a cationic complex = cobalt. Name = Ligands + Metal name (with OS)

Rule 6 (Complex ion is an anion): Metal name ends in –ate + oxidation number.

Anionic Complex Metal Names:

Metal Name in Anionic Complex
Iron Ferrate
Lead Plumbate
Gold Aurate
Chromium (Cr) Chromate
Palladium (Pd) Palladinate
Mercury (Hg) Mercurate
Zinc (Zn) Zincate
Nickel (Ni) Nickelate
Copper Cuprate
Silver Argentate
Tin Stannate
Cobalt (Co) Cobaltate
Platinum (Pt) Platinate
Cadmium (Cd) Cadmate
Aluminium (Al) Aluminate

IUPAC Name Examples

  • Na₂[Fe(CN)₅NO]: Sodium pentacyanonitrosatoferrate(II) (Note: pentacyanonitrosylferrate(II))
  • [Fe(CN)₆]³⁻: hexacyanidoferrate(III) ion
  • [Pt(NH₃)₂(Br)(NO₂)Cl]Cl: triamminebromochloronitroplatinum(IV) chloride
  • K₃[Cr(C₂O₄)₃]: potassium trioxalatochromate(III)

Order of naming ions: Positive ion (cation) first, then negative ion (anion). In naming the complex ion, ligands first (alphabetically), then metal.

Video Tutorials

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