Coordination number polyhedral symbols

Coordination polyhedron Coordination number Polyhedral symbol... 

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. 

Coordination. The number of anions surrounding the specified cation in a crystal structure is referred to as the coordination number, and is shown as a numerical digit in square brackets, e. g. [6] in a chemical formula this symbol is shown as a superscript immediately following the element symbol. The configuration of the coordinating ions is commonly referred to in terms of a polyhedral form the more common of which are shown in Fig. 3. 

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... 

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. 

Figure 7.9 Polyhedral presentations of the three cationconducting polytypes A,f(M,M )O2 based on brucite-like octahedral layers, (a) 03 (b) P2 (c) P3. Small M and M cations are in octahedra, larger A cations are in antiprisms or prisms. The symbols denote coordination ofthe alkali ion (Prism or expanded Octahedron) and number of layers in the hexagonal unit cell (2 or 3) [72].

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