Nomenclature of Coordination Complexes

Appendix. CHEM1902 (C 10K) Coordination Chemistry


From the 2005 IUPAC Inorganic recommendations - the "Red Book"....
The first 'system' of chemical nomenclature was developed by Guyton de Morveau in 1782.[1] Guyton's statement of the need for a 'constant method of denomination, which helps the intelligence and relieves the memory' is still true today.
The first comprehensive report of the IUPAC inorganic commission, in 1940,[2] had a major effect on the systematization of inorganic nomenclature and made many chemists aware of the necessity for developing a more fully systematic nomenclature. These IUPAC recommendations were then revised and issued as a small book in 1959[3] followed by a second revision in 1971[4] and a supplement, entitled 'How to Name an Inorganic Substance', in 1977.[5] In 1990 the IUPAC recommendations were again fully revised[6] in order to bring together the many and varied changes that had occurred in the previous 20 years.
A revision of this so-called Red Book was initiated in 1998. The revised Red Book superseded not only the 1990 Red Book but also, where appropriate, 'Nomenclature of Inorganic Chemistry II -Recommendations 2000' (Red Book II). One of the main changes from the old Red Book was the different organization of material, adopted to improve clarity. Overall, the emphasis on additive nomenclature (generalized from the classical nomenclature of coordination compounds) which was already apparent in the 1990 Red Book, is reinforced.
The latest version of the 'Red Book' was published in Nov 2005 by the Royal Society of Chemistry.

Nomenclature is important in Coordination Chemistry because of the need to have an unambiguous method of describing formulae and writing systematic names, particularly when dealing with isomers. Note however that most textbooks have not implemented the latest IUPAC rules and in some cases have made up their own rules and so should NOT be relied on for guidance.

A simplification of the rules to follow are outlined below:

In a coordination formula, the central atom is listed first.
The formally anionic ligands appear next, listed in alphabetical order according to the first symbols of their formulae. The neutral ligands follow, also in alphabetical order, according to the same principle. The formula of the entire coordination entity, whether charged or not, is enclosed in square brackets.
If the coordination entity is negatively charged, the formula is preceded by the cation formula.
When ligands are polyatomic, their formulae are enclosed in parentheses. Ligand abbreviations are also enclosed in parentheses.

General Reference: Pure Appl. Chem., Vol. 71, No. 8, pp. 1557-1585, 1999.
[1] L.B. Guyton de Morveau, J. Phys., 19, 310 (1782); Ann. Chim. Phys., 1, 24 (1798).
[2] W.P. Jorissen, H. Bassett, A. Damiens, F. Fichter and H. Remy, Ber. Dtsch. Chem. Ges. A, 73, 53 (1940); J. Chem. Soc., 1404 (1940); J. Am. Chem. Soc., 63, 889 (1941).
[3] Nomenclature of Inorganic Chemistry, 1957 Report of CNIC, IUPAC, Butterworths Scientific Publications, London, 1959; J. Am. Chem. Soc., 82, 5523 (1960).
[4] Nomenclature of Inorganic Chemistry. Definitive Rules 1970, Second Edn, Butterworths, London, 1971.
[5] How to Name an Inorganic Substance. A Guide to the Use of Nomenclature of Inorganic Chemistry, Pergamon Press, Oxford, 1977.
[6] Nomenclature of Inorganic Chemistry, Recommendations 1990, Blackwell Scientific Publications, Oxford, 1990.


Note that the 2005 version recommends that ligands will be sorted alphabetically, irrespective of charge.

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 from writing formulae.)

3. Ligand names generally end with 'o' if the ligand is negative ('chlorido' for Cl-, 'cyanido' for CN-, 'hydro' for H-) and unmodified if the ligand is neutral ('methanamine' 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, NiCl2(PPh3)2 is named dichloridobis(triphenylphosphane)nickel(II).

Again, one would use diammine, for (NH3)2, but bis(methylamine), for (NH2Me)2, to make a distinction from dimethylamine. (Note that this ambiguity does not arise if the preferred IUPAC name, methanamine, is used instead of methylamine).
There is no elision of vowels or use of a hyphen, e.g. in tetraammine and similar names. 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 number 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 differed from the 1959 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.
note that it is not necessary to enclose the halogens in brackets.

Note that the 2005 version recommended that anionic ligands end with -ido so that chloro became chlorido, etc.

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