Nomenclature of Coordination Complexes
Nomenclature is important in Coordination Chemistry because of the existence
of isomers. In 1970, the International Union of Pure and Applied Chemistry
(IUPAC), recommended changes to the existing 1957 rules of Inorganic
Nomenclature. However, many textbooks do not use these newer rules and should
NOT be followed for guidance. For example, the 3rd Edition of "Basic Inorganic
Chemistry" by F.A. Cotton, G. Wikinson and P.L. Gaus, John Wiley and Sons, Inc,
1995 page 181, is once again incorrect (the 2nd Edition had it right!).
The rules to follow are outlined below:
1. In naming
the entire complex, the name of the cation is given first and the anion second
(just as for sodium chloride), no matter whether the cation or the anion is the
2. In the complex ion, the name of the ligand or ligands
precedes that of the central metal atom. (This procedure is reversed for writing
3. Ligand names generally end with 'o' if the ligand is
negative ('chloro' for Cl-, 'cyano' for CN-, 'hydrido' for H-) and unmodified if
the ligand is neutral ('methylamine' for MeNH2).
names are 'aqua' for water, 'ammine' for ammonia, 'carbonyl' for CO, 'nitrosyl'
4. A Greek prefix (mono, di, tri, tetra, penta, hexa, etc.)
indicates the number of each ligand (mono is usually omitted for a single ligand
of a given type). If the name of the ligand itself contains the terms mono, di,
tri, eg triphenylphosphine, then the ligand name is enclosed in parentheses and
its number is given with the alternate prefixes bis, tris, tetrakis instead.
For example, Ni(PPh3)2Cl2 is named
To avoid the confusion as to
whether "dimethylamine" means two separate methylamines or the single ligand
dimethylamine, then for the former case it should be named as bis(methylamine).
Some texts suggest that if a ligand is "complicated" then use the bis, tris
multipliers. What constitutes "complicated" is not spelled out however, so a
simpler approach is to use them if the name of the ligand is three or more
5. A Roman numeral or a zero in parentheses is used to
indicate the oxidation state of the central metal atom.
6. If the complex
ion is negative, the name of the metal ends in 'ATE' for example, ferrate,
cuprate, nickelate, cobaltate etc.
7. If more than one ligand is present
in the species, then the ligands are named in alphabetical
order regardless of the number of each. For example, NH3
(ammine) would be considered an 'a' ligand and come before Cl- (chloro). (This
is where the 1971 rules differ from the 1957 rules. Some texts still say that
ligands are named in the order: neutral then anionic).
(i) Some metals in anions have special names
B Borate Au Aurate Ag Argentate Fe Ferrate
Pb Plumbate Sn Stannate Cu Cuprate
(ii) Use of brackets or enclosing marks.
Square brackets are
used to enclose a complex ion or neutral coordination
that it is not necessary to enclose the halogens in brackets.
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Created and maintained by Dr. Robert J. Lancashire,
Department of Chemistry, University of the West Indies,
Mona Campus, Kingston
7, Jamaica.Created March 1996. Links checked and/or
last modified 15th January 2001.