Trigonal bipyramidal configuration

Analysis shows H-bonded chains with coplanar 217 Sn links to phenyl groups in a distorted trigonal bipyramidal configuration. 

Distorted trigonal bipyramidal configuration, 170 with N and Br atoms in frows-positions. Only one diastereoisomer of 36 appears in die solid state. 

Fig. 7. Structures of five-coordinate Cu2+ from first principles molecular dynamics. A Berry twist mechanism for the interconversion of the two structures is shown (from left to right) the reorientation of the main axis of a square pyramidal configuration by pseudo-rotations via a trigonal bipyramidal configuration. The grey atoms in the plane of the trigonal bipyramid are all candidates for becoming apical atoms in a square pyramid.

Fig. 5.17. In-line attack in GTP hydrolysis. Hydrolysis of GTP takes place via an in-tine attack of a water molecnle at the y-phosphate. The reaction passes through a pentavalent transition state in which the ligands of the y-phosphate adopt a trigonal bipyramidal configuration. The mechanism by which the water molecule is activated for the attack on the y-phosphate is not shown in the figure. Possible mechanisms are presented in Fig. 5.18.

The x-ray investigation99 of the crystal KI02F2 has shown that the [IO Fj] ion can also be described as having the trigonal bipyramidal configuration, with the two oxygen atoms and the unshared electron pair in the equatorial positions and the two fluorine atoms at the apices. 

Accounting for the secondary bonds considered above, the total configuration of the tellurium centers in crystalline compounds 89 ought to be octahedral or, in the case of 4,4,-diiodo-l-thia-4-telluracyclohexane, as pentagonal bipyramidal, whereas nonassociated molecules 89 retain a trigonal bipyramidal configuration of bonds formed by the tetracoordinate tellurium centers. 

As can be seen from the following scheme, cleavage of the optically active ate-complex 57 with protons should lead to a chiral, optically active phosphorane, B, provided this has a rigid trigonal-bipyramidal configuration. 

The semiempirical quantum mechanical approximation82-86 that has been called CNDO/2 (for complete neglect of differential overlap) was used to calculate binding energies in the trigonal bipyramidal configuration and in a series of model situations that are pertinent to the TR and the BPR mechanisms in a variety of molecules.81 This approximation to the solution of the LCAO-SCF equations yields results that provide, at least, a trend in the real systems involved. It has been shown that, with reasonable approximations and parametrization, this method offers an adequate compromise with respect to the more rigorous and accurate but far more laborious and expensive ah initio methods.82-85... 

Ligand electronegativity changes may have decisive effects, however, on the symmetry choices of various bipyramidal systems, of which the trigonal bipyramidal configuration is the simplest. 

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