Page 75 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

F O R M U L A E IR-4.6

Where it is not feasible or reasonable t o d efine an oxidation state for each individual
member o f a group (or cluster), the overall oxidation level of the group should b e d efined by
a f ormal ionic charge, indicated as in Section IR-4.3. This avoids the use of fractional
oxidation states.

Examples:

7. O 2
3þ
8. Fe 4 S 4

IR-4.6.2 Formulae of radicals

A r adical is an atom or molecule with one or more unpaired electrons. It may have positive,
negative o r z ero charge. An unpaired electron may be indicated in a f ormula b y a superscript
dot. The dot is placed as a r ight upper index t o t he chemical symbol, so as not to interfere
with indications of mass number, atomic number or composition. In the case of diradicals,
etc., t he superscript dot is preceded by the appropriate superscript multiplier. The radical dot
with its multiplier, if any, precedes any charge. To avoid confusion, the multiplier and the
radical dot can be placed within parentheses.
Metals a nd their ions or complexes often possess unpaired electrons but, by convention,
they are not considered to be radicals, and radical dots are not used in their formulae.
However, there may be occasions when a r adical ligand is bound to a m etal or metal ion
where it is desirable to use a r adical dot.

Examples:

1. H *
2. HO *
*
3. NO 2
2 *
4. O 2
*
5. O 2
* þ
6. BH 3
*2
7. PO 3
8. NO (2 * )
(2 * )2þ
9. N 2

IR-4.6.3 Formulae of optically active compounds

The sign of optical rotation is placed in parentheses, the wavelength (in nm) being indicated
as a r ight subscript. The whole symbol is placed before the formula a nd refers to the sodium
D-line unless otherwise stated.

Example:
1. (þ) 589 -[Co(en) 3 ]Cl 3

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