Isomerization linkage

The activation energy for a reaction represents the energy barrier over which the reactants must pass in being transformed into products. Determining the rate constant (k) as a function of temperature 

However, if the reaction follows this pathway, the transition state should occupy a larger volume than the reactants, so an increase in pressure would decrease the rate of the reaction. Instead, when this reaction was studied at a series of high pressures, it was found that the rate increased with pressure. 

By making a plot of In k versus P, it is possible to determine the volume of activation, AVT For the linkage isomerization reaction shown in Eq. (20.81), the volume of activation is -6.7 0.4cm3 mol-1. Therefore, it can be concluded that the mechanism shown in Eq. (20.81) is not correct. In fact, the negative volume of activation indicates that in the transition state the N02- does not become detached 

Much less frequently studied than the temperature effect on the rate of a reaction is the effect of pres- 

It is possible to derive the following equation that relates the rate constant of a reaction to the applied pressure  

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Spectroscopy at variable temperatures enables us to reveal linkage isomerism of adsorption, when certain molecule fonu with the same site two or more complexes with different geometry and chemical properties. The most studied so far is the case of CO in zeolites, when besides the usual C-bonded complexes with the cations or OH-groups, energetically unfavorable O-bonded complexes ai e formed. 

Ambidentate ligands possess more than 1 donor atom and can coordinate through either one or the other. This leads to the possibility of linkage isomerism (p. 920). The commonest examples are the ions NO2 (p. 463) and SCN (p. 325). Such ligands can also coordinate via both donor sites simultaneously, thereby acting as bridging ligands. 

The rhodium and iridium complexes of dibenzothiophene (L) reveal an interesting case of linkage isomerism (91IC5046). Thus, the ti S) coordinated species [MCp LCb] on thermolysis with silver tetrafluoroborate afford the Ti -coordinated dicationic species. 

Linkage isomerism in metal complexes. J. L. Burmeister, Coord. Chem. Rev., 1968. 3. 225-245... 

Rhodium, iodotetrakis(difluoro(diethylamino)-phosphine)-, 4, 924 Rhodium, pentaamminethiocyanato-base hydrolysis, 1, 504 Rhodium, pentaammincurea-linkage isomerism, 4, 961 Rhodium, pentaammine(urea)-decomposition, 1,186... 

Linkage isomerism This is a special type of structural isomerism in which the differences arise from a particular ligand which may coordinate to a metal ion in more than one way. In Table 1-3 we indicated that a ligand such as thiocyanate could bond to a metal through either the nitrogen or the sulfur atom, and the complex ions [Co(NH3)5(ACS)]2+ and [Co(NH3)5(5CN)]2+ are related as linkage isomers. 

Komiya, S., and Kochi, J.K. (1977) Reversible linkage isomerisms of p-diketonato ligands. Oxygen-bonded and carbon-bonded stmctures in gold(III) acetylacetonate complexes induced by phosphines. Journal of the American Chemical Society, 99, 3695. 

Amides offer both O and N-donors for Co coordination. N-bound amides are accessible through hydrolysis of their corresponding coordinated nitrile or by linkage isomerization of the O-bound form. The preparation of an extensive series of pentaamminecobalt(III) complexes of (monoden-tate-coordinated) amides of the form RCONH2 (R = H, Me, CF3, CH2C1, CH2F, CH=CH2, Ph,... 

The ammonioacetonitrile complex (206) reacts with NH3 to produce the amidine-bonded aminoacetamidine (207) complex, whereas in aqueous base it hydrolyzes to the amid o-A -bo ruled glycinamide complex (208).908 Acid-catalyzed linkage isomerization to first the O-bound form (209) precedes formation ultimately of the amino-bonded isomer (210) as the stable product upon deprotonation of the free amine above pH 6. 

The kinetics of the reaction is first order in both nitrile complex and azide.909 NaN3 reacts with [Co(tetren)(NCMe)]3+ at pH 5.7 to give the 5-methyltetrazolato complex [Co(tetren)(N4CMe)]2+. The reaction is biphasic, involving the initial rapid formation of the AM-bonded tetrazole followed by the slow linkage isomerization to the N2-bonded complex.907... 

When the value for AV is negative, an increase in pressure will increase the rate of reaction. This has been observed for the linkage isomerization reaction (see Chapter 20)... 

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