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 latest (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
complex species.
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 formulae.)
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).
Special ligand names are 'aqua' for water, 'ammine' for ammonia, 'carbonyl' for CO,
'nitrosyl' for NO.
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 dichlorobis(triphenylphosphine)nickel(II).
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 syllables long.
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).
Some additional notes.
(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 species. Examples: [Co(en)3]Cl3 [Co(NH3)3(NO2)3] K2[CoCl4] note that it is not necessary to enclose the halogens in brackets.
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Mar-96, rjl