Trigonal bipyramidal geometries

Pentaphenylantimony [2170-05-0], C3QH23Sb, has attracted considerable attention because it possesses square-pyramidal rather than the expected trigonal-bipyramidal geometry, both ia the sohd state and ia solution. The cyclohexane solvate (C3H ) Sb 1/2 and penta-4-tolylantimony... 

C H Sb, however, both possess trigonal-bipyramidal geometry. In addition to compounds of the type R Sb, mixed compounds of the type R R Sb or R3R 25b, where R and R may be alkyl, alkenyl, alkynyl, or aryl groups, are known. Thus triethyl dimethyl antimony [67576-92-5], CgH2 Sb, has been prepared (197) ... 

The MO picture predicts that the reaction will proceed with inversion of configuration because the development of the transition state is accompanied by rehybridization of the carbon to the trigonal bipyramidal geometry. As the reaction proceeds on to product and sp hybridization is reestablished, the product is formed with inversion of configuration. 

A sterically restricted nucleophile is less reactive than a more accessible one because of nonbonded repulsions which develop in the transition state. The trigonal bipyramidal geometry of the 8 2 transition state is sterically more demanding than the tetrahedral reactant, so steric congestion increases as the transition state is approached. 

In many respects, the successes of this model are remarkable. Iron(O) possesses a total of eight electrons in its valence shell. To satisfy the eighteen-electron rule, five two-electron donors are needed, and compounds such as [Fe(CO)5] are formed. These molecules also obey simple VSEPR precepts, and [Fe(CO)s] adopts a trigonal bipyramidal geometry. Conversely, the use of two five-electron donor ligands such as the strong r-acceptor cyclopentadienyl, Cp, gives the well-known compound ferrocene (9.3). 

It is quite probable that, in the monoorganostannatranes, RSnlOCHjjCHjljN, the tin atom also occupies a trigonal, bipyramidal geometry, but with the organic group forced into an axial site (195,... 

The five-coordinate [Bp]SnMe Cl3 complexes adopt a trigonal bipyramid geometry, with the [Bp] ligand occupying axial and equatorial coordination sites, while the six-coordinate [Tp]SnMe Cl3 n complexes adopt an octahedral geometry (Fig. 34). In solution, however, the com-... 

The X-ray structure of 4rCl(CO)(triphos)] confirms the trigonal-bipyramidal geometry of the Ir center, with the three phosphorus atoms occupying one axial and two equatorial positions and the Cl ligand in the remaining axial position.608... 

Ni—Npyrazoie.572 Tridentate (167) forms five-coordinate [Ni(167)Cl2] with trigonal bipyramidal geometry, while (168) forms octahedral [Ni(168)(H20)2]Cl2. The presence of the basic phenantro-line allows the ligand to stabilize the Nirspecies as revealed by a quasi-reversible NiII/Nil wave at Eii2 = 0.46 V vs. AgCl/Ag+ (for [Ni(167)Cl2]).573... 

A review17 with 25 references of five-coordination in palladium(II) and platinum(II) chemistry is presented. The complexes have invariably a trigonal bipyramidal geometry with the bidentate ligand and the alkene in the equatorial plane. 

Diffusion of solutions containing zinc chloride and crown ethers can give solid state structure where the zinc ion is coordinated to the crown ether oxygens.718 A five-coordinate zinc is observed with distorted trigonal-bipyramidal geometry bound to a chloride, a water molecule,... 

The stability constants of zinc complexes of 4,6-dimethyl-2-thiopyrimidine have been determined by potentiometric measurements. The crystal structure shows infinite zigzag chains of ZnL2 units with each zinc coordinated by an N3S2 donor set in a trigonal-bipyramidal geometry.853... 

A tridentate SNO ligand coordinates with a bipyridine to give ((2,2 -bipyridine)[2-(2-mercapto-phenyl)iminophenoxy])zinc. The monomeric complex has a distorted trigonal bipyramidal geometry with a phenolate and a thiolate coordinated. The synthesis was carried out electrochemically from anodic zinc in the presence of a disulfide-linked ligand precursor.867... 

Figure 2.8 The dipole moment can be used to distinguish between different possible geometries. BrF3 has a nonzero dipole moment and cannot therefore have the symmetrical trigonal bipyramidal geometry. The observed dipole moment is consistent with a square pyramidal geometry.

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