Page 163 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

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

Examples:
1. [PtCl 6 ] 2
2. [Cr(OH 2 ) 6 ] 3þ
III
3. [Cr (NCS) 4 (NH 3 ) 2 ]
III
4. [Cr Cl 3 (OH 2 ) 3 ]
II
5. [Fe (CO) 4 ] 2

IR-9.2.3.4 Use of abbreviations
Abbreviations can be used to represent complicated organic ligands in formulae (although
they should not normally be used in names). When used in formulae they are usually
enclosed in parentheses.
Guidelines for the formulation of ligand abbreviations are given in Section IR-4.4.4;
examples of such abbreviations are listed a lphabetically in Table VII with diagrams of most
shown in Table VIII.
In cases where coordination occurs t hrough one of several possible donor atoms of a
ligand, an indication of that donor atom may be desirable. This may be achieved in names
through use of the kappa convention (see Section IR-9.2.4.2) in which the Greek lower
case kappa (k) i s u sed to indicate the donor atom. To some extent, this device may also be
used in formulae. For e xample, if the glycinate anion (gly) coordinates only through the
nitrogen a tom, the abbreviation of the ligand would be shown a s g ly-kN, a s i n t he complex
[M(gly-kN) 3 X 3 ].

IR-9.2.4 Specifying donor atoms

IR-9.2.4.1 General

There is no need to specify the donor atom of a l igand that has only one atom able to
form a b ond with a c entral atom. However, ambiguity m ay arise when t here is more than
one possible d onor atom in a l igand. It is then necessary t o s pecify which donor atom(s)
of the ligand is (are) bound to the central atom. This includes c ases where a l igand can
þ
be thought of as being formed by removal of H from a p articular s ite in a m olecule or
ion. For example, acetylacetonate, MeCOCHCOMe , h as the systematic ligand name
2,4-dioxopentan-3-ido, which does not, however, imply bonding to the central atom from
the central carbon atom in the ligand. The donor atom can be specified as shown in
IR-9.2.4.2.
The only cases where specification of the donor atom is not required for a l igand that can
bind to a c entral atom in more t han one way are:

monodentate O-bound carboxylate groups
monodentate C-bound cyanide (ligand name ‘cyanido’)
monodentate C-bound carbon monoxide (ligand name ‘carbonyl’)
monodentate N-bound nitrogen m onoxide (ligand n ame ‘ nitrosyl’).
By convention, in these cases t he ligand names imply the binding mode shown.

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