Constants, hydroxo

CO3 species was formed and the X-ray structure solved. It is thought that the carbonate species forms on reaction with water, which was problematic in the selected strategy, as water was produced in the formation of the dialkyl carbonates. Other problems included compound solubility and the stability of the monoalkyl carbonate complex. Van Eldik and co-workers also carried out a detailed kinetic study of the hydration of carbon dioxide and the dehydration of bicarbonate both in the presence and absence of the zinc complex of 1,5,9-triazacyclododecane (12[ane]N3). The zinc hydroxo form is shown to catalyze the hydration reaction and only the aquo complex catalyzes the dehydration of bicarbonate. Kinetic data including second order rate constants were discussed in reference to other model systems and the enzyme carbonic anhy-drase.459 The zinc complex of the tetraamine 1,4,7,10-tetraazacyclododecane (cyclen) was also studied as a catalyst for these reactions in aqueous solution and comparison of activity suggests formation of a bidentate bicarbonate intermediate inhibits the catalytic activity. Van Eldik concludes that a unidentate bicarbonate intermediate is most likely to the active species in the enzyme carbonic anhydrase.460... 

The observed protonation constant describing the proton transfer on the hydroxo oxo complex, is a function of the total metal complex concentration, [MJPoJoh = d[MOH]/[MMt, therefore given by Eq. (17)... 

The line-broadening data as a function of pH, typically shown for the W(IV) in Figs. 13 and 14, incorporating the known pKa values (Table II), were fitted in 5 X 5 Kubo-Sack matrices describing the exchange based on the above schemes (6, 57). The experimentally determined chemical shift and linewidth data in the absence of exchange for the aqua oxo, hydroxo oxo, and dioxo species and the pH-dependent species distribution as calculated from the acid dissociation constants for the four systems were all introduced in the different matrices and the spectra were computer simulated. For each set of chosen rate con-... 

The [TcO(OH2)(CN)4] complex is, as shown by the complex formation constants in Table II, more reactive than the corresponding complexes of either the Re(V) or W(IV). This, coupled with the fact that the dinuclear species [Tc203(CN)8]4 is formed rapidly whenever there are appreciable amounts of the [TcO(OH)(CN)4]2 complex present (71), i.e., below pH ca. 5.5, prohibits any experiment around these acidic conditions. A marked difference in the [H+] dependence for the Tc(V) compared to the above-mentioned Re(V) and W(IV) systems originates from the fact that the Tc(V) is much more reactive and had to be studied at pH values significantly higher than the )Ka2 value of ca. 4. This yielded results similar to the insert (a) in Fig. 16 for the rhenium(V) and only the exchange rate constants and the activation parameters for the hydroxo oxo complex for Tc(V) could thus be obtained (Table V). 

The constants given for reactions (v), (vi) and (vii) are representative of those of a ligand containing a carboxylic acid and a phenolic hydroxo group. 

Speciation of Pb(II) in Glatt river. The concentrations given for CO2, Pb(II), Cu(II) and [Ca2+] as well as for the pollutants EDTA and NTA are representative of concentrations encountered in this river, The speciation is calculated from the surface complex formation constants determined with the particles of the river and the stability constants of the hydroxo-, carbonate-, NTA- and EDTA-complexes.The presence of [Ca2+] and [Cu2+] is considered. 

Although, the first reaction step, reduction of the Fe(III) to the Fe(II) porph5rrin complex by KO2, could not be studied in detail because of interference of the formation of the Fe(III) hydroxo species, the second reaction step, binding of superoxide to the Fe(II) species and formation of the Fe(III)-peroxo complex, could be studied in detail 61). To our knowledge, for the first time superoxide concentration (Fig. 11) and temperature dependent kinetic studies of reactions with superoxide have been performed by stopped-fiow UVA is measurements, and as a result the second-order rate constant ( on = 36,500 + 500 s )... 

It is common to use the overall stability constant, where p = number of metal, q = number of hydrogens (for protonated species), and r = number of ligands. The value of q is negative for hydroxo species. For the reaction to form ML,... 

Table 11 Rate constants and activation volumes for complex formation from the hexa-aqua- and hydroxo-aqua forms of iron(III), in aqueous solution at 298.2 K.

Tab. 9.1 Equilibria and experimentally determined stability constants for the iron hydroxo complexes (room temperature).

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