Beryllium hydrolysis species

Figure 7.1 Structures of the beryllium hydrolysis species. The open bonds are in the plane of the page, the closed bonds come out of the page, and the hatched bonds go into the page. Each coloured area denotes a separate species.

The predominant polymeric beryllium hydrolysis species that forms is Be3(OH)3 . The formation of the species has been confirmed by nuclear magnetic resonance studies (Akitt and Duncan, 1980 Akitt and Elders, 1988) and has also been identified in the solid state (Cecconi et al., 1998). The beryllium ion is tetrahedral and contains four waters of hydration, and in the Be3(OH)3 species each beryllium atom is bound to two hydroxide molecules with the other two tetrahedral positions occupied by water molecules (see Figure 7.1). Thus, the complete formula of the species is Be3(0H)3(H20)g with the three beryllium and three hydroxide ions forming a six-membered ring that has a... 

Soboleva etal. (1977) also provided data on the solubility of bromellite (BeO(s)). They studied the solubility of this phase over the temperature range of 150-250 °C but provided thermodynamic data over the larger range of 25-300 C. From the solubility study, they provided data for the stability constants of the beryllium hydrolysis species, BeOH", Be(OH)2(aq) and Be(OH)3 , as well as that of the... 

Data reported for the stability constant of polymeric beryllium hydrolysis species are listed in Table 7.4. For the majority of species, the data cover a relatively narrow range of temperature. Data have also been acquired for the enthalpy of reaction for all of the polymeric species that are believed to form. The accepted species include Be20H , Be3(OH)3 ", Beg(OH)g and Beg(OH)g. ... 

There have been three studies that have used calorimetry to determine the enthalpies of reaction of the polymeric beryllium hydrolysis species (Carell and Olin, 1962 Ishiguro and Ohtaki, 1979 Alderighi et al., 1998). In addition, Mesmer and Baes (1967) measured the stability constants of these species over the temperature range of 0-60 "C from which the enthalpies of reaction were deduced. Finally, Ciavatta and Grimaldi (1973) determined the polymeric stability constants at 60 "C and in 3 moll NaClO. The stability constant values obtained in their study can be compared with those obtained at 25 "C in 3 mol 1" NaClO and the enthalpy data of Carell and Olin (1962) acquired under the same conditions. These data are presented in Table 7.6. 

Carell and Olin (58) were the first to derive thermodynamic functions relating to beryllium hydrolysis. They determined the enthalpy and entropy of formation of the species Be2(OH)3+ and Be3(OH)3+. Subsequently, Mesmer and Baes determined the enthalpies for these two species from the temperature variation of the respective equilibrium constants. They also determined a value for the species Be5(OH) + (66). Ishiguro and Ohtaki measured the enthalpies of formation of Be2(OH)3+ and Be3(OH)3+ calorimetrically in solution in water and water/dioxan mixtures (99). The agreement between the values is satisfactory considering the fact that they were obtained with different chemical models and ionic media. 

In comparison with other metal ions, the stability of BeOH is relatively weak at 25 °C. Polymeric species predominate in acidic solutions at beryllium concentrations above 10 molkg . Consequently, few studies of beryllium hydrolysis have been able to measure the stabUity of BeOH at this temperature. At higher temperatures, the monomers become more stable than the polymers, and, as a result, only monomers have been detected at high temperatures. 

Table 7.3 Data for the stability constants of beryllium monomeric hydrolysis species (reaction (2.5), M = p = 1). 

The zinc complex formed with V,V -diphenylformamidinate is structurally analogous to the basic zinc acetate structure, as [Zn4(/i4-0)L6], and the basic beryllium acetate structure. It is prepared by hydrolysis of zinc bis(diphenylformamidinate).184 Mixed metal zinc lithium species were assembled from dimethyl zinc, t-butyl lithium, V.iV -diphenylbenzamidine and molecular oxygen. The amidinate compounds formed are dependent on the solvent and conditions. Zn2Li2 and... 

The addition of soluble carbonates to beryllium salt solutions gives only basic carbonates. Beryllium salt solutions also have the property of dissolving additional amounts of the oxide or hydroxide. This behavior is attributable to the formation of complex species with Be—OH—Be or Be—O—Be bridges. The rapidly established equilibria involved in the hydrolysis of the [Be(H20)4]2+ ion are very complicated and depend on the anion, the concentration, the temperature, and the pH. The main species, which will achieve four-coordination by additional water molecules, are considered to be Be2(OH)3+ and Be3(OH)3+ (probably cyclic). 

Beryllium chemistry includes its S-diketonate complexes formed from dimedone (9), acetylacetone and some other S-diketones such as a,a,a-trifluoroacetylacetone. However, unlike the monomeric chelate products from acetylacetone and its fluorinated derivative, the enolate species of dimedone (9) cannot form chelates and as the complex is polymeric, it cannot be distilled and is more labile to hydrolysis, as might be expected for an unstabilized alkoxide. However, dimedone has a gas phase deprotonation enthalpy of 1418 9 kJmoD while acetylacetone enol (the more stable tautomer) is somewhat less acidic with a deprotonation enthalpy of 1438 10 klmoD Accordingly, had beryllium acetylacetonate not been a chelate, this species would have been more, not less, susceptible to hydrolysis. There is a formal similarity (roughly 7r-isoelectronic structures) between cyclic S-diketonates and complexes of dimedone with benzene and poly acetylene (10). The difference between the enthalpies of formation of these hydrocarbons is ca... 

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