Page 145 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

I N O R G A N I C A C I D S A N D D E R I V A T I V E S IR-8.4

dihydrogen(tetraoxidochromate)
12. H 2 CrO 4

13. HCrO 4 hydrogen(tetraoxidochromate)(1 )
dihydrogen(heptaoxidodichromate)
14. H 2 Cr 2 O 7
15. H 2 O 2 dihydrogen(peroxide)

16. HO 2 hydrogen(peroxide)(1 )
17. H 2 S d ihydrogen(sulfide)
þ dihydrogen(trioxidonitrate)(1þ)
18. H 2 NO 3
Note the difference from compositional names such as ‘hydrogen peroxide’ for H 2 O 2 and
‘hydrogen sulfide’ for H 2 S ( Chapter IR-5) in which (in English) there is a s pace between the
electropositive and electronegative component(s) o f t he name.
Compositional names of the above type, containing the word ‘hydrogen’, w ere classified
as ‘hydrogen nomenclature’ in the discussion of oxoacids in Section I-9.5 of Ref. 2, and such
names were extensively e xemplified. However, in order to avoid ambiguity, their general
use is not encouraged h ere. Consider, for example, that the compositional names ‘hydrogen
sulfide’ and ‘hydrogen sulfide(2 )’ can both be interpreted as H 2 S a s w ell as HS . T he
situation w ith H 2 S i s c ompletely analogous to that with Na 2 S w hich may be named sodium
sulfide, disodium sulfide, sodium sulfide(2 ) a nd disodium sulfide(2 ), except t hat

misinterpretation of the first and third names as denoting NaS is improbable. In Ref. 2, the

names ‘hydrogensulfide(1 )’ and ‘monohydrogensulfide’ for HS were proposed to avoid
ambiguity. (However, i n s ome l anguages there is no space in compositional names so that
very delicate distinctions are required anyway.)
The strict definition of hydrogen names proposed here is meant to eliminate such
confusion by imposing the requirements:

(i) that ‘hydrogen’ be attached to the rest of the name,
(ii) that the number of hydrogens must be specified by a m ultiplicative prefix,
(iii) t hat the anionic part be placed in enclosing marks, and
(iv) t hat the charge of the total structure being named is specified.

Hydrogen names constructed i n t his way cannot be mistaken for other t ypes of name.
The only acceptable exceptions to the above format for hydrogen names are the few
particular abbreviated anion n ames listed in Section IR-8.5.
In a f ew cases, no confusion can arise, and the distinction between compositional name
and hydrogen name i s n ot as important, m ost notably for the hydrogen halides. T hus, HCl
can equally unambiguously b e n amed ‘hydrogen chloride’ (compositional name) and
‘hydrogen(chloride)’ (hydrogen name).
Examples 1, 3–6 and 14 above demonstrate that homo- and heteropolyoxoacids and their
partially d ehydronated forms can be given hydrogen names once the corresponding anions
have been named. Examples 4–6 e ach feature three alternatives. The first two names are both
fully additive for the anion p art and correspond to different ways o f d issecting the structure
into ligands and central atoms. The last names, involving the prefixes ‘ silico’ and ‘phospho’,
are examples of a c ommon semi-systematic nomenclature which is not recommended f or
general use because it requires c omplex conventions in order to be unambiguous.

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