Polyhedral symbol

Table 1. Polyhedral Symbols for Common Coordination Geometries ...

The approach adopted is to view the molecule in three dimensions, imagining each atom or group to be placed at a vertex of hn appropriate polyhedron. In organic chemistry this is usually the tetrahedron with carbon at the centre. Table 3.3 (p. 18) shows the polyhedra normally encountered in organic and inorganic chemistry. It also includes for each polyhedron the polyhedral symbols to denote shape and coordination number. It is to be noted that these polyhedra are often presented in a highly formalised fashion. An octahedron is often represented with the apices rather than the octahedral faces depicted, thus ... 

A Inclusion of structural information. The names described so far detail ligands and central atoms, but give no information on stereochemistry. The coordination number and shape of the coordination polyhedron may be denoted, if desired, by a polyhedral symbol. These are listed in Table 4.4. Such a symbol is used as an affix in parentheses, and immediately precedes the name, separated from it by a hyphen. This device is not often used. 

Different geometrical arrangements of the atoms attached to the central atom are possible for all coordination numbers greater than one. The coordination polyhedron (or polygon in planar molecules) may be denoted in the name by an affix called the polyhedral symbol. This descriptor clearly distinguishes isomers differing in the geometries of their coordination polyhedra. 

List oi polyhedral symbols Coordination Coordmoiion Polyhedrd... 

Since the descriptors cis and trans are not generally applicable for octahedral coordination compounds, systematic descriptors based on the CIP system should be used in their place. These consist of the polyhedral symbol, in... 

Polyhedral. symbol. The polyhedral symbol indicates the geometrical arrangements of the coordinating atoms about the central atom. It consists of one or more capital italic letters derived from common geometric terms which denote the idealized geometry of the ligands around the coordination center, and an arabic numeral that is the coordination number of the central atom. The polyhedral symbol is used as an affix, enclosed in... 

Coordination polyhedron Coordination number Polyhedral symbol... 

Distortions from idealized geometries commonly occur. However, it is normal practice to relate molecular structures to idealized models. The polyhedral symbol is used as an affix, enclosed in parentheses and separated from the name by a hyphen. The polyhedral symbols for the most common geometries for coordination numbers 2 to 9 are given in Table IR-9.2 and the corresponding structures and/or polyhedra are shown in Table IR-9.3. 

Table IR-9.3 Polyhedral symbols, geometrical structures and/or polyhedra...

The configuration index for a square planar system is placed after the polyhedral symbol (SP-4). It is the single digit which is the priority number for the ligating atom trans to the ligating atom of priority number 1, i.e. the priority number of the ligating atom trans to the most preferred ligating atom. 

The configuration index of an octahedral system follows the polyhedral symbol (OC-6) and consists of two digits. 

The configuration index for T-shaped systems follows the polyhedral symbol and consists of a single digit, the priority number of the ligating atom on the stem of the T (as opposed to the crosspiece of the T). 

Example 4 shows the compound [CoBr2(en)(NH3)2]+ which has the polyhedral symbol OC-6 and the configuration index 32. The chirality symbol is C. 

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