Trigonal bipyramidal structur

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].

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. 

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). 

Why is the structure square-pyramidal It has been shown that a diamagnetic d6 ML5 complex distorts away from the Jahn-Teller active trigonal bipyramidal structure.20 Two more stable structures are possible a square pyramid (T) and a distorted trigonal bipyramid (Y). Theoretical studies21 have shown that the T and Y structures are very close in energy and that the preference for one over the other comes from a subtle balance of a and it properties of the ligands. 

Perhaps the most fruitful of these studies was the radiolysis of HCo(C0)4 in a Kr matrix (61,62). Free radicals detected in the irradiated material corresponded to processes of H-Co fission, electron capture, H-atom additions and clustering. Initial examination at 77 K or lower temperatures revealed the presence of two radicals, Co(C0)4 and HCo(C0)4 , having similar geometries (IV and V) and electronic structures. Both have practically all of the unpaired spin-density confined to nuclei located on the three-fold axis, in Co 3dz2, C 2s or H Is orbitals. Under certain conditions, a radical product of hydrogen-atom addition, H2Co(C0)3, was observed this species is believed to have a distorted trigonal bipyramidal structure in which the H-atoms occupy apical positions. 

The nitrosyls RuH(NO)(PR3)3 are 5-coordinate with trigonal bipyramidal structures and linear Ru-N-O geometries the hydride and nitrosyl ligands occupy the apical positions (for RuH(NO)(PPh3)3, z/(Ru-H) 1970 cm-1, i/(N—O) 1640 cm-1 H NMR, 8 = +6.6 ppm for the hydride resonance). The high-field NMR line is a quartet showing coupling with three equivalent phosphines, which would not be possible in a square pyramidal... 

Although the majority of complexes have structures that are linear, tetrahedral, square planar, or octahedral, a few compounds have a trigonal bipyramid structure. Most notable of these are Fe(CO)5, Ni(CN)5ji, and [Co(CN)5]3T Some complexes having a coordination number of 5 have the square-base pyramid structure, including [Ni(CN)5 3. Although it is not particularly common, the coordination number 8 is found in the complex [Mn(CN)8]4-, which has a cubic structure with CIST ions on the corners. 

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