Page 177 - 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. [Be 4 (m 4 -O)(m-O 2 CMe) 6 ]
0
hexakis(m-acetato-kO:kO )-m 4 -oxido-tetrahedro-tetraberyllium
2. [Os 3 (CO) 12 ]
4
4
4
dodecacarbonyl-1k C,2k C,3k C-triangulo-triosmium(3 Os—Os)
(The descriptors tetrahedro and triangulo are introduced in Section IR-9.2.5.7.)
Another such case is Example 5 i n S ection IR-9.2.5.2 where it is immaterial which of the
two cobalt a toms is given number 2 a nd which one number 3. The systematic name w ill be
the same.
The proposed general procedure for constructing a c oordination-type additive name for a
polynuclear entity i s a s f ollows:

(i) Identify the central atoms and ligands.
(ii) Name the ligands, i ncluding k, Z and m designators (except for the central atom
locants). Note that ligand names may have to be modified if k, Z or m symbols apply
only to some p ortions of the ligand that are otherwise equivalent (and described by a
multiplicative prefix such as ‘tri’ or ‘tris’).
(iii) Place ligand names in alphabetical order.
(iv) Assign central atom locants by applying the following rules:
(a) Apply the element sequence of Table VI. The later an element is met when
following the arrows, t he lower its locant number. This criterion will determine
the numbering if all central atoms are different elements. Locants may be assigned
to atoms of the same element by applying the next rules.
(b) Within each class of identical central atoms, assign lower locant numbers to
central atoms with higher c oordination numbers.
(c) Proceed through the alphabetical list of ligand names. Examine the names or name
parts specifying ligating atoms explicitly (as in a k or Z designator) or implicitly
(as in the ligand name ‘ carbonyl’). As soon as a s ubset of ligating atoms is met
which is not evenly distributed among the central atoms still awaiting t he
assignment of distinct locant numbers, t he central atoms with the most l igating
atoms of this kind are given the lowest numbers available. This process of
sequential examination of the ligands is continued u ntil all central atoms have
been assigned locants or all ligands have been considered.
(d) Any central atoms that are inequivalent and have not yet been assigned distinct
locant numbers will differ only in the other c entral atoms to which they are
directly bonded. The locant numbers of these directly bonded neighbouring
central atoms are compared a nd the central atom with the lowest-locant
neighbouring atoms is given t he lowest of the remaining p ossible l ocants (see
Example 9 b elow).

Note that the central atom locants assigned using these rules need not coincide w ith those
assigned when using other t ypes o f n omenclature such as substitutive nomenclature (cf.
Chapter I R-6), i f t hat is applicable, or the nomenclature systems described in Chapters II-1
or II-5 of Ref. 7.

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