Page 26 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

IR-2.2 G R A M M A R

other structural features of species; geometrical and structural p refixes a re listed in Table V.
The ordering o f p refixes i n s ubstitutive nomenclature is dealt with in Chapter I R-6, and in
additive nomenclature in Chapters IR-7, IR-9 and IR-10.
Other devices may be used to complete the description o f t he compound. These include
the charge number to indicate the ionic charge, e.g. hexaaquacobalt(2þ), and, alternatively,
the oxidation number to indicate the oxidation state of the central atom, e.g.
hexaaquacobalt(II).
The designation of central atom and ligands, g enerally straightforward i n m ononuclear
complexes, is more difficult in polynuclear compounds where there are several central
atoms in the compound to be named, e.g. in polynuclear coordination compounds, and
chain and ring c ompounds. In each case, a priority order or hierarchy has to be established.
A h ierarchy of functional groups is an established feature of substitutive nomenclature;
Table VI shows a n e lement sequence used in compositional and additive nomenclature.
The purpose o f t his Chapter is to guide the users o f n omenclature in building the name o r
formula of an inorganic compound and to help them verify that the derived name o r f ormula
fully obeys the accepted principles. The various devices used in names (or formulae) are
described successively b elow, together with their meanings and fields of application.

IR-2.2 E N C L O S I N G M A R K S

IR-2.2.1 General
Chemical n omenclature employs three types o f e nclosing mark, namely: braces {}, square
brackets [ ] , a nd parentheses ( ) .
In formulae, t hese enclosing marks are used in the following nesting order: [ ] , [ ( ) ], [{( )}],
[({( )})], [ {({( )})}], etc. S quare brackets a re normally used only to enclose entire formulae;
parentheses and braces are then used alternately (see also Sections IR-4.2.3 and IR-9.2.3.2).
There are, however, s ome specific uses of square brackets i n f ormulae, cf. Section IR-2.2.2.1.
In names, t he nesting order is: ( ) , [ ( ) ], {[( )]}, ({[( )]}), etc. This ordering is that used
in substitutive nomenclature, see Section P-16.4 of Ref. 1. (See also Section IR-9.2.2.3 for
the use of enclosing marks with ligand names.)

Example:
1. [Rh 3 Cl(m-Cl)(CO) 3 {m 3 -Ph 2 PCH 2 P(Ph)CH 2 PPh 2 } 2 ] þ

Ph +
Ph P 2 P PPh 2
O C 2 C O 3 Cl
Rh 1 Rh Rh
Cl O C
Ph P 2 P PPh 2
Ph

2
tricarbonyl-1kC,2kC,3kC-m-chlorido-1:2k Cl-chlorido-3kCl-bis{m 3 -
0
bis[(diphenylphosphanyl)methyl]-1kP:3kP -phenylphosphane-2kP}trirhodium(1þ)

17