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Nomenclature of Complex Compounds

1. If the compound is ionic, the name of cation is mentioned first followed by the name of anion.

For the non-ionic complexes the name of complex is written as one word.

2. In naming the complex, the names of the ligands are written first followed by the name of the central ion. The oxidation number of the central metal atom is expressed by Roman numeral in parentheses just after the name of the central metal atom.
 3. Naming of ligands.

 (a) For the ligands carrying a negative charge the name has a characteristic ending “o”. A few example are:

CI                   – chloro

p                     – fluoro

I-                               –  iodo

CN                  -cyano

NO3               – trioxonitrato(V)

SO4 2- –           tetraoxosulphato(VI)

(b) For the ligands carrying a positive charge, the name of the ligand has a characteristic ending of “ium “. Fo1 example,

NO 2+ – nitronium

(c) For neutral ligands no characteristic ending is used For example,

The following examples are, however, exceptions:

H2O – aqua,                 NO – nitrosy l,

NH3 – ammine,            CO- carbonyl.


4. Order of naming ligands. According to ol. conventions, the names· of more than one type of ligand surrounding the central atom are written in the order (i) Negative (ii) Neutral (iii) Positive, without separating the1 with a hyphen.

According to the latest IUPAC conventions the name. of ligands surrounding the central metal atom are written in alphabetical order of preference irrespective of whether they are negative or neutral. In the present text the new IUPAC system has bee followed.

5. The number of each kind of ligands are specified the prefixes di, tri, tetra, etc. If the ligand is complex, such . ethylenediamine (en), and is repeated two, three or four time then the words bis, tris, tetrakis, etc., are used, followed I the name of the ligand in parentheses.

6. Ending of name of the central atom. Names of complex cations and neutral molecules have no distinguishing termination but in the case of anionic complexes the suffix “ate” is attached to the name of central atom. For example, K4[Ni(CN)4] is named as Potassium tetracyanonickelate (O).

7. The oxidation state of the central metal atom or ion is designated by a Roman numeral (1, II, III, etc.) in the bracket at the end of the name of the complex without a gap between the two.

Some examples illustrating the above rules are given below:



potassium hexachloroplatinate(IV)


2. CO(NH3)5Cl) Cl2

pentamminechlorocobalt(III) chloride


3. [Ni(NH3)4 Cl2]



4. [CO(NH3) 6] 3+

hexaamminecobalt(III) ion


5. K4[Fe(CN)6]

potassium hexacyanoferrate(II)


6. [CO(en)3] Cl3

tris (ethylenediamine) cobalt(III) chloride


7. Ni(CO)4

tetracarbonylnickel (0)


8. K4[Cr(CN)6]

Potassium  hexacyanochromate(II)


9. [CrCI2(H2O)4]+

tetraaquadichlorochromium(III) ion


10. [Cu (NH3)4]2+

tetraamminecopper(II) ion