Bipyramidal structure skew-trapezoidal

Distortion of the trans octahedral structure to the skew-trapezoidal bipyramidal structure 58... 

Compounds containing two bidentate. ligands and two chemically similar unidentate ligands can exist as the usual cis and trans octahedral isomers, or as the skew-trapezoidal bipyramidal structure observed for bidentate ligands of small normalized bite. However, a different stereochemistry, which can be represented as a pentagonal pyramid, is found under the combined conditions of small normalized bite and a large difference between the natures of the two unidentate ligands. 

Complexes containing two bidentate and two unidentate ligands may be either cis or trans octahedral, but it is important to note that both stractures show very large distortions as the size of the chelate rings is reduced the trans structure turns into the skew-trapezoidal bipyramidal stmcture (Figure 2). 

Important examples of this skew trapezoidal bipyramid structure are the dialkyltin complexes with four-membered... 

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