Trigonal bipyramidal/octahedral structures

Section 8.13 molecular structure valence shell electron-pair repulsion (VSEPR) model linear structure trigonal planar structure tetrahedral structure trigonal pyramid trigonal bipyramid octahedral structure square planar structure... 

Organotin compounds are divalent (Sn(II)) and tetravalent (Sn(IV)) and the coordination numbers of 2, 3, 4, 5, 6 and 7 are known. The 3, 4, 5, 6 and 7 coordination correspond to trigonal, tetrahedral, trigonal bipyramidal, octahedral and pentagonal bipyramidal structures, respectively. 

Tin exists in the +2 state, called the lower valence state, and the +4 state, called the higher valence state. While most of these compoimds are tetrahedral, some form octahedral and, less often, trigonal bipyramid organometalhc structures. 

Complexes of titanium(III) can be made from the trichloride— these are either approximately octahedral, 6-coordinate (for example TiClj.SL (L = ligand) and [TiCljfHjOj, formed when TiCls dissolves in aqueous hydrochloric acid), or 5-coordinate with a trigonal bipyramid structure. 

The same group198 characterized the complexes of methyltin halides with dibenzyl, diethyl and methyl benzyl sulphoxides. R3SnCl forms complexes with one and R2SnCl2 with two donor molecules, and trigonal bipyramidal and octahedral structures, respectively, were suggested for these complexes as shown in Scheme 16. 

Phosphorous (V) fluorides have some interesting structural and dynamic features that influence their 19F NMR spectra. All such compounds appear to have a trigonal bipyramid structure, which features two axial and three equatorial sites. Hexafluorophosphate, PF6 , is of course octahedral with all sites equivalent (Scheme 7.6). 

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