Page 170 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

IR-9.2 C O O R D I N A T I O N C O M P O U N D S

IR-9.2.4.3 Comparison of the eta and kappa conventions
The eta convention (Section IR-10.2.5.1) is applied in cases w here contiguous d onor atoms
within a g iven l igand are involved in bonding to a c entral atom. Thus, it is used only when
1
there is more than one ligating atom, and the term Z is not used. The contiguous a toms are
often the same element, but need not be.
The kappa convention is used to specify bonding f rom isolated donor atoms to one or
more central atoms.
In cases w here two or more identical ligands (or parts of a p olydentate ligand) are
bound to a c entral atom, a s uperscript is used on k to indicate the number of donor
atom-to-central a tom bonds.

IR-9.2.4.4 Use of donor atom symbol alone in names
In certain c ases t he kappa convention may be simplified. Donor atoms of a l igand may be
denoted by adding only the italicized symbol(s) for the donor atom (or atoms) to the end of
the name of the ligand. Thus, for the 1,2-dithiooxalate anion, ligand names such as 1,2-
0
dithiooxalato-kS,kS and 1,2-dithiooxalato-kO,kS may, with no possibility of confusion, be
shortened t o 1 ,2-dithiooxalato-S,S and 1,2-dithiooxalato-O,S, r espectively. Other examples
0
are thiocyanato-N and thiocyanato-S, a nd nitrito-N and nitrito-O.

IR-9.2.5 Polynuclear complexes

IR-9.2.5.1 General

Polynuclear inorganic complexes exist in a b ewildering array of structural types, such as
ionic solids, molecular polymers, extended assemblies of oxoanions, chains and rings,
bridged metal complexes, and homonuclear and heteronuclear clusters. This section
primarily treats t he nomenclature of bridged metal complexes and homonuclear and
heteronuclear clusters. Coordination polymers are treated extensively e lsewhere. 6
As a g eneral principle, as much structural i nformation as possible s hould b e p resented
when writing the formula o r n ame o f a p olynuclear complex. However, polynuclear
complexes may have structures s o l arge and extended as to make a r ational structure-based
nomenclature impractical. Furthermore, their structures may be undefined o r n ot suitably
elucidated. In such cases, the principal function o f t he name or formula is to convey the
stoichiometric proportions of the various moieties p resent.
In the present and following sections, particular complexes are often used as examples
several times to show how they may be named differently according to whether o nly
stoichiometry is to be specified or partial or complete structural information is to be
included.
Ligands in polynuclear complexes are cited in alphabetical order both in formulae
and names. The number of each ligand is specified by subscript numerical multipliers in
formulae (Sections IR-9.2.3.1 to IR-9.2.3.4) and by appropriate multiplicative prefixes
in names (Sections IR-9.2.2.1 to IR-9.2.2.3). The number of central atoms of a g iven k ind, if
greater than one, is indicated similarly.

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