Trigonal bipyramidal species

In trigonal bipyramidal EX5, there are two types of X atom axial and equatorial. This leads to the possibility of stereoisomerism when more than one type of substituent is attached to the central atom. Iron pentacarbonyl, Fe(CO)5, is trigonal bipyramidal and when one CO is exchanged for PPh3, two stereoisomers are possible depending on whether the PPh3 ligand is axially (2.38) or equatorially (2.39) sited. 

In contrast to a single ( t) bond where free rotation is generally assumed, rotation about a double bond is not a low energy process. The presence of a double bond may therefore lead to stereoisomerism as is observed for N2F2. Each N atom carries a lone pair as well as forming one N—F single bond and an N=N double bond. Structures 2.43 and 2.44 show the trans- and cw-isomers respectively 0fN2F2. 

For trigonal bipyramidal EX2Y3, three stereoisomers (2.40 to 2.42) are possible depending on the relative positions 

In a trigonal bipyramidal species, stereoisomerism arises because of the presence of axial and equatorial sites. 

For trigonal bipyramidal EX2Y3, three stereoisomers (2.40 to 2.42) are possible depending on the relative positions of the X atoms. Steric factors may dictate which isomer is preferred for a given species e.g. in the static stmcture of PCI3F2, the F atoms occupy the two axial sites, and the larger Cl atoms reside in the equatorial plane. 

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Trigonal-bipyramidal species and nucleophilic displacement reactivity The 3c/4e cu-bonding motif can also be achieved in nonlinear polyatomics by backside attack of a nucleophile X - on a polar Y—Z bond of a conventional Lewis-structure molecule,... 

The reductive elimination reactions of halogen from 6-11 illustrate several examples of ligand loss from trigonal bipyramidal species B to generate onium species A. Activation parameters in these processes were of 73 to 100 kJ mol and Eyring activation parameters of 70-97 kJ molfor and —4 to... 

Basal CN. b Apical CN. 5 Distorted trigonal bipyramidal species. d Square pyramidal species. 

The complexes of stoichiometry [Fe(terpy)X2] (X = Br, I, or NCS) are probably five-coordinate trigonal-bipyramidal species (385), whereas [Fe(terpy)Cl2], which was originally thought to possess a similar structure (75, 76,243,271,388,389), has been shown to be [Fe(terpy)2][FeCl4] (385). 

The trigonal bipyramidal species that forms during the reaction and then rearranges to give products may exist either as an activated complex or as a true intermediate. The distinction between the two depends essentially on the lifetime of the species. The term activated complex refers to the configuration of reactants and... 

Organometallic compounds of rhodium have the metal center in oxidation states ranging from +4 to -3. but the most common oxidation states are +1 and +3. The Rh(I) species have a d electron configuration and both four coordinated square planar and five coordinated trigonal bipyramidal species exist. Oxidative addition reactions to Rh(I) form Rh(III) species with octahedral geometry. The oxidative addition is reversible in many cases, and this makes catalytic transformations of organic compounds possible. Presented here are important reactions of rhodium complexes in catalytic and stoichiometric transformations of organic compounds. 

The relationship between mechanistic type and reaction stereochemistry is not a priori as clear cut as with reactions at carbon, since the trigonal bipyramidal species involved is an intermediate, which can in principle pseudorotate, rather than a transition state. In practice this appears to happen only in the case of 1,2-migrations, where according to Westheimer s rules, the intermediate phosphorane must pseudorotate. 

R. K. Sheline et al. 137,441,442) presented IR spectroscopic evidence for Cr(CO)5, Mo(CO)5 and W(CO)5 by low temperature irradiation of the corresponding carbonyls in isopentane-methylcyclohexane glasses. The IR data obtained are consistent with Cm symmetry for all three (square pyramidal) pentacarbonyls. On warming up carefully the glass with Mo(CO)5 a transformation to a trigonal bipyramidal species with Dzu symmetry occurs. 

CH2=CH2 R = Ph, L = MeCN). These complexes exhibit square-planar coordination with a bidentate Tp ligand, with the exception of [PtMe(CH2=CH2)(Tp )] trigonal bipyramidal. [PtMe(Tp )(CO)] is present in solution in both isomeric forms the four-coordinate square-planar and five-coordinate trigonal-bipyramid species rapidly interconvert in solution. The structures of [Pt(Me)(MeCN)(ic2-HTp )][BArF], [Pt(Me)(K2-HTp )(L)][BArF] (L = CO, CH2=CH2, PMe2Ph), fr ws-[Pt(Me)(K1-HTp )(PMe2Ph)2][BArF], and of the neutral square planar complex [PtMe(Tp )(SMe2)] have been determined by single-crystal X-ray study.520... 

Figure 2a shows a field-swept ESEM spectrum of Cu in a hydrated CsNa-A sample this shows two Cu + species. For each species the ESEM pattern has been determined at both gll and gi and satisfactorily simulated with the same parameters. One Cu h species is located at site S2 at the center of the six-ring. The second Cu + species is located at site S2 displaced 0.09 nm into the 8-cage. Fr previous ESEM work with adsorbed D2O it is known that these two Cu species are coordinated to two and three water molecules respectively. (14) The Cu + species at S2 is a trigonal bipyramidal species with three equatorial lattice oxygens and two axial water molecules. The species at S2 is a distorted octahedral species coordinated to three lattice oxygens and three water molecules. 

In unstrained substrates it is possible that a discrete adduct does not form, but that the trigonal bipyramidal species is the high point, that is, the transition state, on the energy level-reaction coordinate profile. 

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