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Principal and auxiliary valencies; IUPAC names

Short answer

Principal valency is the ionizable oxidation state satisfied by ions outside the coordination sphere; auxiliary valency is the non-ionizable coordination number, directional, satisfied by ligands directly bonded. Example: [Co(NH3)6]Cl3 has principal valency 3 and auxiliary 6. IUPAC names: a) sodium dicyanoargentate(I), b) tetraammineaquachlorocobalt(III) chloride, c) tris(ethylenediamine)chromium(III) chloride, d) potassium hexachloromanganate(II).

What are principle and auxiliary valencies of the metal in the complex compounds? Illustrate with suitable example. Write the IUPAC names of a) Na[Ag(CN)₂] b) [Co(NH₃)₄H₂O.Cl]Cl₂ c) [Cr(en)₃]Cl₃ d) K₄[Mn(Cl)₆]

Principal (primary) and auxiliary (secondary) valencies

  • Principal valency: the ionisable valency of the metal, equal to its oxidation state, satisfied by negative ions. It is shown by dotted lines.
  • Auxiliary valency: the non-ionisable valency, equal to the coordination number, satisfied by ligands (neutral or negative) attached directly to the metal. It is shown by solid lines and has a fixed direction in space.

Example: in [Co(NH₃)₆]Cl₃, the principal valency is 3 (satisfied by 3 Cl⁻ outside the bracket) and the auxiliary valency is 6 (satisfied by 6 NH₃). In [Co(NH₃)₅Cl]Cl₂, Cl⁻ inside satisfies both valencies.

IUPAC names

a) Na[Ag(CN)₂]: sodium dicyanoargentate(I) b) [Co(NH₃)₄(H₂O)Cl]Cl₂: tetraammineaquachlorocobalt(III) chloride c) [Cr(en)₃]Cl₃: tris(ethylenediamine)chromium(III) chloride d) K₄[MnCl₆]: potassium hexachloromanganate(II)

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