Hydroxo species

This is probably too simple, hydroxo species such as [M04(0H)2] being more likely. 

In aqueous solution the An02" ions (An = Pa Am) may be formed, at least in the absence of strongly coordinating ligands. They are linear cations like An02 + but are less persistent and, indeed, it is probable that Pa02" should be formulated as [PaO(OH)2]" " and [PaO(OH)]. Hydrolysis is extensive in aqueous solutions of Pa and colloidal hydroxo species are formed which readily lead to precipitation of... 

A pyrolylnickel complex 21 also could activate water to afford a bridging hydroxo complex 22 accompanying cleavage of the Ni-carbon bond (Eq. 6.12) [20]. The hydride (hydroxo) species was not observed in the reaction mixture. 

Herberhold reported activation of water with Re2(CO)io. The reaction proceeded at 200°C to give a tetranuclear complex [Re(CO)3( X -OH)]4 (23) in quantitative yield, and evolution of dihydrogen and CO was observed (Eq. 6.13) [21]. Complex 23 has a pseudo-cubane structure without metal-metal bonds in which the Re(CO)3 groups are linked by triply-bridging OH ligands. Also in this case, no presumed intermediate hydrido(hydroxo) species was detected. 

Fig. 3. Calculated distribution of beryllium hydroxo species in acid conditions, (a) CBe = 0.2 M, (b) CBs = 0.002 M.

Fig. 7. Calculated distribution diagram of beiyllium hydroxo species, CBb = 0.002 M.

The hydroxo species isoelectronic with a fluoride does not always exist in the vapor, but its enthalpy can be estimated by summing heats of the component oxides ... 

There is however the possibility, especially with trivalent ions, and within given pH-ranges, that surface hydroxo species can be formed. 

The autoprotolysis of water can be included into the algorithm in a very compact way. As already indicated in Table 1, hydroxo species are given the notation H i. According to equation (3.22) we can write ... 

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 )... 

An [H + ] term in the rate law for reactions involving an aqua redox partner strongly suggests the participation of an hydroxo species and the operation of an inner-sphere redox reaction (Sec. 5.5(a)). Methods (a) and (b) are direct ones for characterizing inner-sphere processes, analyzing for products or intermediates which are kinetically-controlled. Method (c) is indirect. Other methods of distinguishing between the two basic mechanisms are also necessarily indirect. They are based on patterns of reactivity, often constructed from data for authentic inner-sphere and outer-sphere processes. They will be discussed in a later section. 

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,... 

All three hydroxo species [M(OEP)(Me)(OH)] (M = P, As, Sb]) are sufficiently acidic to react with the aluminum porphyrin complex Al(OEP)Me, which is known to eliminate methane on reaction with protic reagents. Three novel binuclear... 

The aquo-Fe " ion, [Fe(OH2)6], is the predominant Fe " species only at very low pH. As the pH rises above 1, Fe " hydrolyses in a stepwise manner to give a series of soluble, positive and (in alkaline media) negative hydroxo species (see Chap. 13). The different hydrolysis species raise the concentration of dissolved iron in equilibrium with the solid at any pH. The equilibrium between the solid oxide and its various hydroxo species in solution is represented by the equation ... 

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