Coordination Compounds

hexaamminecobalt(III) chloride

NH₃ = ammine (double m); × 6 = hexaammine; Co(III) = cobalt(III); counter ion Cl⁻ = chloride. Name: hexaamminecobalt(III) chloride. Note: 'ammine' not 'amine' — this is an IUPAC-specific spelling.

Potassium hexacyanidoferrate(III)

The complex is an anion [Fe(CN)₆]³⁻ → metal gets -ate suffix: Fe → ferrate. OS of Fe: x + 6(−1) = −3 → x = +3 → ferrate(III). Counter ion K⁺ = potassium. Name: potassium hexacyanidoferrate(III).

+2

OS of Fe: x + 6(−1) = −4 (charge of complex ion). x = −4 + 6 = +2. Fe is in +2 oxidation state. The compound is potassium hexacyanidoferrate(II).

Oxidation state

Werner's primary valency = oxidation state of the metal. It is ionisable and satisfied only by negative ions (counter ions). Secondary valency = coordination number.