Bipyramidal structure

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 stereochemistry of Mg and the heavier alkaline earth metals is more flexible than that of Be and, in addition to occasional compounds which feature low coordination numbers (2, 3 and 4), there are many examples of 6, 8 and 12 coordination, some with 7, 9 or 10 coordination, and even some with coordination numbers as high as 22 or 24, as in SrCdn, BaCdn and (Ca, Sr or Ba)Zni3. " Strontium is 5-coordinate on the hemisolvate [Sr(OC6H2Bu3)2(thf)3]. jthf which features a distorted trigonal bipyramidal structure with the two aryloxides in equatorial positions. ... 

Turning finally to compounds with bonds from the heavier Group 14 elements to heavier Group 15 elements we may note compounds such as [Sn C(PMe2)3)2] which has the pseudo trigonal bipyramidal structure (6). This complex, which has Sn bonded exclusively to four P atoms, is formed as yellow crystals by the... 

Figure 22.8 The trigonal bipyramidal structure of [VOCh(NMe3)2].

As for the previous oxidation state, the chemistries of Mo" and W" are much more extensive than that of Cr" whieh is largely confined to peroxo- and fiuoro- complexes. [Cr(02)2(NH3)3], which has a dark red-brown metallic lustre, may be obtained either by treating [Cr(02)4] " with warm aqueous ammonia or by the action of H2O2 on ammoniacal solutions of (NH4)2Cr04. It has a pentagonal bipyramidal structure in which the peroxo- groups oeeupy... 

A transition-state structure was proposed on the basis of the solid-state structure of [Ni((R,R)-DBF0X)(H20)3](C104)2 (Fig. 1.8). The catalyst-dienophUe complex is thought to be a square-bipyramidal structure containing an octahedral nickel ion. The dienophile adopts an s-cis conformation with the si face shielded by a phenyl group. 

Many of the nitrosyls studied are 5-coordinate, and analysis of crystallographic results indicates that, in general, in the trigonal bipyramid structures NO is found in the equatorial position in a linear geometry whereas in a square pyramidal structure, there is a bent M—N—O linkage in an apical position. A further point of interest is that in compounds like Ir(NO)Cl2(PPh3)2, the nitrosyl group bends in the more hindered (P—Ir—P) plane. 

Molecules of the deep blue-black compound AuI3(PMe3)2 have a trigonal bipyramidal structure in which Au-P is 2.333-2.347 A and Au-I is 2.709-2.761 A. It is prepared by the reaction of gold metal with Me3PI2 [138b]... 

Iron(II) complexes of general formula [FeLA2] A = Cl, Br, I, NO3, NCS or NCSe have been formed [145] with both 2-formylquinohne thiosemicarbazone, 20, and 1-formylisoquinoline thiosemicarbazone, 21. All are characterized as five-coordinate, high spin iron(II) complexes and the electronic spectra are assigned consistent with distorted trigonal bipyramidal structures. 

The X-ray structure of (347), PR3 = PMe3, confirms the trigonal-bipyramidal structure, with the olefin and phosphine ligands lying in the equatorial plane. The equilibrium between free and bound olefin depends on the size of the tertiary phosphine. Further reaction of (347) with IrCl(CO)(PMe3)2 results in formation of a bimetallic iridacyclobutene complex by a second-order process. 

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