Sulfate, formation constants with

Exciting developments have occurred in the coordination chemistry of the alkali metals during the last few years that have completely rejuvenated what appeared to be a largely predictable and worked-out area of chemistry. Conventional beliefs had reinforced the predominant impression of very weak coordinating ability, and had rationalized this in terms of the relatively large size and low charge of the cations M+. On this view, stability of coordination complexes should diminish in the sequence Li>Na>K>Rb> Cs, and this is frequently observed, though the reverse sequence is also known for the formation constants of, for example, the weak complexes with sulfate, peroxosulfate, thiosulfate and the hexacyanoferrates in aqueous solutions. 

An iron-selective electrode based on a glass Fe-1173 (Ge2sSbx2Seeo) has been reported to respond to xmcomplexed iron(ni) in sulfate solutions. It was used to evaluate formation constants of iron(III)-sulfate complexes and as an indicator for titrations of sulfate with barium. The mechanism of the sensing action is obscure. 

Ce(nr) also forms complexes with sulfate. Newton and Arcand estimated the formation constant of the species CeS04 to be 2.4 x 10 at zero ionic strength and found that it decreased rapidly with increasing ionic strength, until at unit ionic strength the formation constant was estimated to be about 18. 

Weak complexes form between vanadate and phosphate, 9,99 pyrophosphate,59 arsenate,59 and chromate.106 The formation constant for the simple phosphovanadate is about 20 M 1." Structural characterization has been reported for interesting cluster structures of vanadium with organophosphonates107 and with sulfate.108 Divanadium(V) complexes with either monodentate or bidentate nitrate (N03 ) groups have been reported.109... 

Spectroscopic, conductimeiric, and kinetic evidence have been used to establish the degree to which a complex is of outer- or inner-sphere character (cf. Nancollas 1966 Shaw et al. 1991). As noted above, the formation constants of many divalent metal-sulfate complexes are practically identical, consistent with a dominantly outer-sphere character. In fact, the sulfate pairs of divalent Mg, Zn, Ni, Co, Mn, and Be (log Ar ssocCBeSO ) = 1.95) have been shown to have about 10% inner-sphere character (Nancollas 1966). The greater stabilities of PbSO (log / assoc 2.69) and UO2SO4 (log /iTassoc =... 

Experimentally, water exchange rate constants are mainly determined from nuclear magnetic resonance measurements [6, 7]. Other techniques are restricted to very slow reactions (classical kinetic methods using isotopic substitution) or are indirect methods, such as ultrasound absorption, where the rate constants are estimated from complex-formation reactions with sulfate [3]. The microscopic nature of the mechanism of the exchange reaction is not directly accessible by experimental methods. In general, reaction mechanisms can be deduced by experimentally testing the sensitivity of the reaction rate to a variety of chemical and physical parameters such as temperature, pressure, or concentration. 

Nearly all of the formation constants listed in Table 8.8 are for complexes formed by Am(iii), as little work has been done on complexes of americium with oxidation states higher than iii. Color changes indicate existence of Am(vi) nitrate, sulfate, and fluoride complexes. There is also spectrophotometric evidence [299] for the existence in 1 m NaOH solution of a peroxide complex of... 

Singh, S.S. and Brydon, J.E. (1969) Solubility of basic aluminium sulfates at equilibrium in solution and in the presence of montmorillonite. Soil ScL, 107, 12—16. Sipos, P., Capewell, S.G., May, P.M., Hefter, G.T, Laurenczy, G., Lukacs, F., and Roulet, R. (1997) tI-NMR and UV-Vis spectroscopic determination of the formation constants of aqueous thallium(l) hydroxo-complexes. J. Solution Chem., 26, 419-431. Srinivasan, K. and Rechnitz, G.A. (1968) Reaction rate measurements with fluoride ion-selective membrane electrode. Formation kinetics of ferrous fluoride and aluminium fluoride complexes. Anal. Chem., 40, 1818-1825. 

Since the free sulfate ion concentration in seawater (S = 35) is on the order of 0.0095 mol kg and varies with temperature by no more than approximately 20%, the concentration of lanthanide sulfate species in seawater remains nearly constant relative to free metal ion concentrations ([MSOJ]/[M ] w 0.8). Consideration of the formation of M(S04)2 species in seawater, with zero ionic strength formation constants on the order of log 804)82 5.2, results in predicted M(S04)2 concentrations which are on the order of 10% as large as free lanthanide ion concentrations in seawater. 

Diethyl ether is the principal by-product of the reaction of ethyl alcohol with diethyl sulfate. Various methods have been proposed to diminish its formation (70—72), including separation of diethyl sulfate from the reaction product. Diethyl sulfate not only causes an increase in ether formation but is also more difficult to hydroly2e to alcohol than is ethyl hydrogen sulfate. The equiUbrium constant for the hydrolysis of ethyl hydrogen sulfate is independent of temperature, and the reaction rate is proportional to the hydrogen ion concentration (73—75). 

The physical nature of the sulfate complexes formed by plutonium(III) and plutonium(IV) in 1 M acid 2 M ionic strength perchlorate media has been inferred from thermodynamic parameters for complexation reactions and acid dependence of stability constants. The stability constants of 1 1 and 1 2 complexes were determined by solvent extraction and ion-exchange techniques, and the thermodynamic parameters calculated from the temperature dependence of the stability constants. The data are consistent with the formation of complexes of the form PuSOi,(n-2)+ for the 1 1 complexes of both plutonium(III) and plutonium(IV). The second HSO4 ligand appears to be added without deprotonation in both systems to form complexes of the form PuSOifHSOit(n"3) +. ... 

---