Coordination polyhedral

Intermediate between the extended four-coordinate connectivities that dominate the low- T solid phase and the two-coordinate ring/chain connectivities that dominate at higher T are certain //jree-coordinate polyhedral structures that retain a degree of cooperative proton ordering. Two examples of such trigonally coordinated buckyball clusters, a 24-mer and a 28-mer, are shown in Fig. 5.31. The... 

List of polyhedral symbols Coordination Coordination Polyhedral... 

The interpretation of the observed proton and C PCS led to the conclusion that the two structural isomers are enantiomeric pairs of diastereoisomers differing in the octadentate ligand conformation, namely, capped square antiprismatic (SA or M) and twisted capped square antipris-matic (TSA or m) geometries, respectively (Figure 5). " The Ln + coordination polyhedral of SA and TSA have two opposite parallel faces occupied by the ligand ring nitrogen... 

Lalik, E. (2005). Shannon Information as a Measure of Distortion in Coordination Polyhedral, /. Appl Cryst, Vol.38,152-157... 

The third rule further concerns the linkage of the cation coordination polyhedral. In a stable structure, the corners, rather than the edges and especially the faces of coordination polyhedra, tend to be shared. If an edge is shared, it tends to be shortened. The fourth rule says that polyhedra formed about the cations of low coordination number and high charge tend especially to be linked by corner sharing. The fifth rule states that the number of different constituents in a structure tends to be small. 

It is often difficult to represent inorganic compounds with the usual structure models because these structures are based on complex crystals space groups), aggregates, or metal lattices. Therefore, these compounds are represented by individual polyhedral coordination of the ligands such as the octahedron or tetrahedron Figure 2-124d). 

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

As a result of the systematic application of coordination-chemistry principles, dozens of previously unsuspected stnicture types have been synthesized in which polyhedral boranes or their anions can be considered to act as ligands which donate electron density to metal centres, thereby forming novel metallaboranc elusters, ". Some 40 metals have been found to act as acceptors in this way (see also p. 178). The ideas have been particularly helpful m emphasizing the close interconnection between several previously separated branches of chemistry, notably boron hydride clu.ster chemistry, metallaboranc and metallacarbaborane chemistry (pp. 189-95). organometallic chemistry and metal-metal cluster chemistry. All are now seen to be parts of a coherent whole. 

Nomenclature follows the well-established oxa-aza convention of organic chemistry. Numbering begins with the apex atom of lowest coordination and successive rings or belts of polyhedral vertex atoms are numbered in a clockwise direction with C atoms being given the lowest possible numbers within these rules. ... 

It can be seen that although the Si-O bond distances within the polyhedral skeleton are not unusually long (cf. an average distance of 1.629 A for four-coordinate Si attached to two coordinate the Si-O-Si angles, varying from about 114.5 to 118.5°, are much sharper than is common in unstrained systems... 

The symmetry of five-coordinate zinc complexes has been analyzed using continuous symmetry measures. This approach and the computational tool allow the degree of polyhedricity to be evaluated quantitatively. The methodology identifies the minimal distance of a given structure to a desired general shape with the same number of vertices.27... 

This, together with the Ir-H terminal bond indicates that the compound can be regarded as a further example of the growing number of compounds in which the high oxidation state Ir(v) is stabilized by coordination to a soft polyhedral borane ligand... 

Fig. 8. Polyhedral representation of the Keggin structure (central tetrahedral atom not shown). The lines seen in the center are the edges of the V30i3 subunit at the back (cf. also Fig. 21). Black dots indicate where one of the two five-coordinate capping units are attached in [Vi5042]9 .

Fig. 2.3-27. Molecular structure of 82 (only the N atoms directly bonded to the Ca atoms are shown). The first coordination sphere around the central Ga atom is shown in a polyhedral representation.

Fig. 7. Structure of the singly-bridged Au-oxo complex, 3. Top left, combination polyhedral/ball-and-stick representation right, thermal ellipsoid plot. The PO4 and WOe polyhedra (or W atom) are shown in lighter and darker gray. Bottom left. X-ray structure of the coordination polyhedron...

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