Square antiprism theories

Calculations, based on VSEPR theory so as to minimize repulsion between ligands in some of these afore-mentioned forms, have shown that repulsion energy coefficients for the square antiprism, dodecahedron, and cube are about the same but that the antiprism should be the most stable configuration for a MLg polyhedron (S). This principle has also been applied to K4[Mo(CN)g] 2H20, for which, in contrast... 

Rationalize the structure of [XeFg] (a square antiprism) in terms of VSEPR theory. 

A study of a number of other compounds which are generally considered to be among the most completely ionic shows that cubic coordination is not confined to the alkali halides. It occurs, for example, in the fluorite structure in which many ionic MXa compounds crystallize. On the other hand the isolated [Tab s]3 group has the square antiprism arrangement (64) predicted by the simple theory. This underlines a point of great importance to the understanding of ionic crystal structures, namely, that the requirement that a structure can be extended indefinitely in space imposes severe restrictions on the types of coordination which are possible. Cubic coordination can be extended indefinitely, but it is not possible to form an extended... 

Beryllium, bis(t ifluo oacetylacetone)-gas chromatography, 560 Berzelius s conjugate theory, 4 Bicapped pentagonal prisms repulsion energy coefficients, 34 twelve-coordinate compounds, 100 Bicapped square antiprisms repulsion energy coefficients, 33,34 ten-eoordinate compounds, 98 1, r-Binaphthyl, 2,2 -bis(diphenylphosphino)-complexes... 

In the field of large coordination numbers different geometries can be energetically very similar (77). This applies especially to coordination number 8. The atoms bonded to the metal can be arranged at the comers of a cube, as a square antiprism, or as a dodecahedron. The compound [Mo(CN)g] exemplifies this class and is dodecahedral, which the VSEPR would predict as very likely, but we are now stretching the theory to its very limit. This [MLg] structure appears to have 2 electrons not involved in dictating the geometry. 

For the most part, the structures of noble-gas compounds follow readily from VSEPR theory. In the gas phase, xenon hexafluoride assumes a nonrigid, slightly distorted octahedral structure, even though it has seven electron pairs around the central xenon atom. In the solid, it is characterized by square pyramidal XeF cations bridged by fluoride ions. XeF is a square antiprism, and XeOF4 is nearly a perfect square pyramid. 

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