Page 89 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

C O M P O S I T I O N A L N O M E N C L A T U R E I R-5.5

Examples:
7. K 2 O d ipotassium oxide
dipotassium (dioxide), or potassium dioxide(2 )
8. K 2 O 2
monopotassium (dioxide), or potassium dioxide(1 )
9. KO 2
10. KO 3 potassium (trioxide), or potassium trioxide(1 )

Clearly, a simple s toichiometric name l ike ‘potassium dioxide’, although strictly speaking
unambiguous (referring to the compound in Example 9), could e asily be misinterpreted. I n
other cases, based on chemical knowledge, there is no chance o f m isinterpretation in
practice, and the simple stoichiometric name w ill m ost o ften be used, as in Examples 11
and 12 below.

Examples:
barium dioxide (simple stoichiometric name), or barium (dioxide)
11. BaO 2
or barium dioxide(2 ) ( specifying the diatomic anion), or barium
peroxide (using the acceptable alternative name for the anion)
manganese dioxide (simple stoichiometric name), or manganese
12. MnO 2
bis(oxide) (specifies two oxide ions rather than a d iatomic anion),
or manganese(IV) oxide

IR-5.5 N A M E S O F ( F O R M A L ) A D D I T I O N C O M P O U N D S

The term addition compounds covers d onor-acceptor complexes (adducts) and a v ariety o f
lattice compounds. The m ethod described here, h owever, is relevant n ot just to such
compounds, but also to multiple s alts and to certain compounds of uncertain structure or
compounds for which the full structure need not be communicated.
The names of the individual components o f s uch a g eneralized addition compound are
each constructed by using an appropriate nomenclature system, w hether c ompositional,
substitutive or additive. The overall name of the compound is then formed by connecting the
names of the components b y ‘ em’ dashes; the proportions of the components are indicated
after the name b y a stoichiometric descriptor consisting of arabic numerals separated by a
solidus or solidi. T he descriptor, in parentheses, is separated from the compound name b y a
space. The order of names of the individual components is, firstly, according to the
increasing number of the components a nd, secondly, alphabetical. A s t he only exception,
the component name ‘water’ is always cited last. (Note that this represents a c hange from the
rule in Ref. 2 a ccording to which the component names must follow the order given by
the formula.) The numerals in the descriptor appear in the same o rder as the corresponding
component names.
For addition compounds containing water as a c omponent, the class name ‘ hydrates’ is
acceptable because of well established use, even though t he ending ‘ate’ might seem to
indicate an anionic component. F or hydrates with a s imple stoichiometry, names of the
classical ‘hydrate’ type are acceptable, but rules have not been formulated for non-integer
stoichiometries such as that in Example 12 below. Also, because of their ambiguity, the

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