Coordination Compounds: Rules for Nomenclature of Coordination Compounds (For CBSE, ICSE, IAS, NET, NRA 2022)

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Oxidation Number

  • Oxidation number of the metal is equal to the charge of the complex ion if the ligands do not bear the net charge.
  • For example, in each is neutral, so the oxidation number of copper is .
  • The net charge on the complex ion is the sum of the charges on the central atom and its surrounding ligands.
  • For example, ion , each chloride ion has an oxidation number of , the oxidation number of must be .

Rules for Nomenclature of Coordination Compounds

  • The cation is named before the anion, as in other ionic compounds. The rule holds regardless of whether the complex ion bears a net positive or a negative charge. For example, in and compound, named first.
  • Within a complex ligands are named first, in alphabetical order, and the metal ion is named last.
  • The name of anionic ligand ends with the letter , whereas a neutral ligand is usually called by the name of the molecule. The exceptions are (aqua) , (carbonyl) and (ammine) . The table given below lists some common legands.

Some Common Ligands

Illustration 2 for Some_common_ligands
  • When several ligands of a particular kind are present, we use the Greek prefix di, tri- tetra etc. to name them. Thus, the ligands in cation are named as “tetraammine dichloro” . If the ligand itself contains a Greek prefix, we use the prefixes bis, tris and tetrakis etc. to indicate the number of ligands present. For example, the ligand ethylenediamine already contains , therefore, if two such ligands are present the name is bis (ethylenediamine) .
  • The oxidation number of the metal is written in roman numerals following the name of the metal. For example, the roman numeral III is used to indicate the oxidation state of chromium in , which is named tetraamminedi chloro chromium (III) ion.
  • If the complex is an anion, its name ends in – ate. For example, in the anion is called hexacyanoferrate (II) ion. The table given below give the name of anions containing central atoms.

Some Anions Containing Metal Atoms

Illustration 3 for Some_anions_containing_metal_atoms

If the complex is either a cation or is neutral, no change is required in the name of the central metal ion. For example, and are named as hexaamminecobalt (III) ion and tetracarbonyl nickel (0) , respectively.

Few Examples to show naming in coordination compound is shown below:

  • hexaaquacobalt (III) chloride
  • potassium hex chloroplatinate (IV)
  • diamminetetra chloroplatinic (IV)
  • dichlorobis (ethylenediamine) cobalt (III) chloride.

Valence Bond Theory

This theory has account reasonably well for the structure and magnetic properties of metal complexes.

The basic principles involved in the valence bond treatment of coordination compound are:

  • Hybridization of valance orbitals of the central metal/ion
  • Bonding between ligand and the metal ion/atom.
  • Relation between the type of bond and the observed magnetic Behaviour.

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