Complexes Nomenclature

Rules for Nomenclature of Complexes

1.     Split the complex molecule into its cation and anion.

2.   In complex, cation is named first, followed (after a space) by the name of the anion (regardless of which is the complex ion)

3.     In complex ion (whether cation or anion) or in neutral complex, all ligands are named first [which are listed together as one word without any separation by hyphens] followed by the name of the central atom with its oxidation state in roman numerals in parenthesis. The suffix –ate is used in name of central atom (can use the Latin root) in case of –ive complex ion before the oxidation state. [The name of central atom is unchanged in case of cationic complex or neutral complex]. e.g.

4.   All ligands are listed in alphabetic order. If there are two or more ligands of the same type (say negative), these are listed in alphabetic order (disregarding the prefixes).

(a)   Names of negative ligands are written as ending in –O.  If the name of the compound ligands ends with –ide, –ite or –ate, it is changed respectively to –ido, –ito or –ato. [For some simple ligand, the ending –ide is changed simply to –O e.g. F^– – Fluoro, OH¯ – Hydroxo].

Ligands or Co-ordinating Groups and its Types 

Ambidentate Ligand

The ligands that can legate through two different atoms present in its molecule to central atom or ion are called Ambidentate Ligand. Some ambidentate ligands are NO₂^–, SCN^– or NCS^– etc.

1. The ligand NO₂^– can attach itself through N (as – NO₂^–) as well as through O (as ONO^–). The – NO₂^– is named as nitro and ONO^– is named as nitrito.

2.  The ligand CNS^– may get attached through S (as – SCN^–) or through N (as – NCS^–). The ligand – SCN^– is named as thiocyanato or thiocyanato–S and the ligand – NCS^– is named as isothiocyanato or thiocyanatio–N. 

Classification of Ligands According to Charge

According to charge, ligands are of three types namely anionic, neutral and cationic ligands. The name of anionic ligands end in –O while cationic ligand have suffix –ium.

1. Anionic Ligands or Negative Ligands

2. Neutral Ligands or Molecular Ligands

3. Cationic Ligands or Positive Ligands

           Anionic Ligands or Negative Ligands

The ligands which carry negative charge on them are called anionic ligands. Anionic ligands generally form anionic complex ions. If the name of the ligands end –ide, –ite, or –ate , it is changed respectively to –ido, –ito, or –ato. For some simple ligands, the ending –ide is changed simply to –O. e.g.