Page 13 - 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-9.3

The C/A assignment for polydentate ligands is illustrated by Example 6 w hich uses the
priming convention developed in Section IR-9.3.5. Note that priority number 2 h as
higher priority than 2 . 0

Example:

6.
1

2 1'

M

3 2'

3'
Chirality symbol = A

IR-9.3.4.9 The C/A convention for trigonal prismatic centres

For the trigonal p rismatic system, the configuration index is derived from the CIP priority
numbers of the ligating atoms opposite the triangular f ace containing the greater number
of ligating atoms of highest CIP priority. The chirality symbol is assigned by viewing
the trigonal p rism from above the preferred triangular face and noting t he direction of
progression of the priority sequence for the less preferred triangular f ace.

Examples:

1. 2.
1 2 2 1
3 3

5 6 4 6

4 5

Chirality symbol ¼ C Chirality symbol ¼ A

IR-9.3.4.10 The C/A convention for other bipyramidal c entres
The procedure used for the trigonal b ipyramid is appropriate for other bipyramidal structures.
The structure is assigned the symbol C or A, a ccording to whether the clockwise (C)
or anticlockwise (A) s equence is lower at the first point of difference when the numbers are
compared d igit by digit from one end to the other (see Sections IR-9.3.4.5 and IR-9.3.4.6) and
the molecule is viewed from the higher p riority ligating atom on the reference axis.

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