Page 185 - 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

square planar, square p yramidal or tetrahedral. The coordination p olyhedron ( or polygon
in planar molecules) may be denoted in the name by an affix called t he polyhedral symbol.
This descriptor distinguishes isomers d iffering in the geometries of their coordination
polyhedra.
The polyhedral symbol must be assigned before any other s patial features can be
considered. It consists of one or more c apital italic letters derived from common geometric
terms which denote the idealized g eometry of the ligands around the coordination centre,
and an arabic numeral that is the coordination number of the central atom.
Distortions from idealized g eometries commonly occur. H owever, it is normal
practice to relate molecular structures to idealized m odels. T he polyhedral symbol is
used as an affix, e nclosed in parentheses and separated from the name b y a hyphen. The
polyhedral symbols for the most common geometries for coordination numbers 2 t o 9 are
given in Table IR-9.2 and the corresponding structures and/or polyhedra are shown in
Table IR-9.3.

Table IR-9.2 Polyhedral symbols a

Coordination Coordination Polyhedral
polyhedron number symbol

linear 2 L-2
angular 2 A-2
trigonal plane 3 TP-3
trigonal pyramid 3 TPY-3
T-shape 3 TS-3
tetrahedron 4 T-4
square plane 4 SP-4
square pyramid 4 SPY-4
see-saw 4 SS-4
trigonal bipyramid 5 TBPY-5
square pyramid 5 SPY-5
octahedron 6 OC-6
trigonal prism 6 TPR-6
pentagonal bipyramid 7 PBPY-7
octahedron, face monocapped 7 OCF-7
trigonal prism, square-face monocapped 7 TPRS-7
cube 8 CU-8
square antiprism 8 SAPR-8
dodecahedron 8 DD-8
hexagonal bipyramid 8 HBPY-8
octahedron, trans-bicapped 8 OCT-8
trigonal prism, triangular-face bicapped 8 TPRT-8
trigonal prism, square-face bicapped 8 TPRS-8
trigonal prism, square-face tricapped 9 TPRS-9
heptagonal bipyramid 9 HBPY-9

a
Strictly, not all geometries can be represented by polyhedra.

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