Complexes sulfato

Concentrated sulfuric acid (97 wt %) at 300—400°C has been used to solubili2e niobium from columbite and pyrochlore (18,19). The exothermic reaction is performed in iron or siUcon-iron cmcibles to yield a stable sulfato complex. The complex is filtered free of residue and is hydroly2ed by dilution with water and boiling to yield niobic acid which is removed by filtration as a white coUoidal precipitate. 

The separation of basic precipitates of hydrous Th02 from the lanthanides in monazite sands has been outlined in Fig. 30.1 (p. 1230). These precipitates may then be dissolved in nitric acid and the thorium extracted into tributyl phosphate, (Bu"0)3PO, diluted with kerosene. In the case of Canadian production, the uranium ores are leached with sulfuric acid and the anionic sulfato complex of U preferentially absorbed onto an anion exchange resin. The Th is separated from Fe, A1 and other metals in the liquor by solvent extraction. 

U1 "1" (16), and Np1 "1" (17) (Table IV). Only in the thorium system have stability constants been determined as a function of acidity. Zebroski et al., (12) found that the 1 2 complex had the form TMSOi, at 0.5 M and 1.0 M acidity but suggested a contribution from the monoprotonated, bis-sulfato complex in 2 M acid. However, Zielen (9) found no evidence for such a species. The Kj/K2 ratio found in the latter study (n.8) compares favorably with the Am(III)-S0 data of DeCarvalho and Choppin (10)... 

Benkelberg, H.-J., and P. Warneck, Photodecomposition of Iron(III) Hydroxo and Sulfato Complexes in Aqueous Solution Wavelength Dependence of OH and SO/ Quantum Yields, J. Phys. Chem., 99, 5215-5221 (1995). 

Tellurium(IV) sulfato complexes of composition 2(2Te02 S03),MHS04-2H20 have been reported,46 from which the anhydrous compounds were obtained by calcination. Carboxylic acids have also been found to form anionic complexes with tellurium(IV) and polonium(IV). For example, the silver salts of the citrato- and tartrato-tellurates(IV) have been described47 as insoluble in water but soluble in nitric acid. 

Sulfato complexes of chromium(II) are known, and the insolubility of the monohydrogen phosphate Cr(HP04) 4H20 suggests anion coordination (Section 35.3.5.1). 

The nitratocomplexes MIAm02(N03)3 (M1 = Rb or Cs424) are precipitated from nitric acid solutions of americium(VI). The IR spectrum of RbAm02(N03)3 has been reported.249 Hydrated phosphato, arsenato and sulfato complex salts are included under Aqua species in the preceding section. 

X-Ray diffraction studies of aqueous CdS04 solutions have clearly demonstrated the formation of O-sulfato complexes.668-670 These are of the general form [Cd(H20)6- (0S03) ](2-2")+, and appear to be the major species present in concentrated solutions. These results are fully in accord with tensimetric studies of the cadmium and magnesium sulfate aqueous systems, which indicate an increased interionic attraction at elevated temperatures.671 In contrast, X-ray diffraction studies on cadmium perchlorate solutions show no evidence for the coordination of the perchlorate ion to the metal, the only cationic species present being [Cd(H20)6]2+(Cd—O, 2.292 A, cf. Cd—O, 2.292 A in solid [Cd(H20)6][C104]2),670... 

Ionization isomers differ by the exchange of a ligand with an anion or neutral molecule outside the coordination sphere. For instance, [CoBr(NH3)5]S04 and [CoS04(NH3)5]Br are ionization isomers because the Br ion is a ligand of the cobalt in the former but an accompanying anion in the latter. The two compounds have different physical properties the bromo complex is violet and the sulfato complex is red. The chemical properties of the two ionization isomers are also different the red isomer forms an off-white precipitate of AgBr when Agf ions are added, but no precipitate forms after the addition of Ba2-1- ... 

Simpler Ligands. Composition data (Table I) of the sea include aquo, halo (Cl", Br", F"), carbonato, and sulfato complexes. Since the pH of our average ocean is 8.1, hydroxo complexes would also be important, as might be phosphate complexes. Except for the halides, ligands important to marine science are almost routinely overlooked by most coordination chemists. Fortunately there are exceptions, as noted from the papers in this volume. 

Titanium(IV)-porphyrin [TiO(TPP)] as well as molybdenum(V)-porphyrin [MoO(OMe)(TPP)] complexes were found to be active for the catalytic epoxidation of alkenes by alkyl hydroperoxides, whereas their peroxo derivatives are inactive.632 Iron(III)-porphyrin-peroxo complexes such as Fe(TPP)02NMe4 did not react with hydrocarbons, but form sulfato complexes upon reaction with S02.632 Manganese(III)-porphyrin-peroxo complexes Mn(02)(TPP) K+ were recently characterized by X-ray crystallography.634... 

As was observed in the case of the extraction of zirconium and hafnium from nitrate media, it is probable that the different tendencies of the metals towards hydrolysis has some effect on the selectivity observed,298 313 expecially in view of the proved extraction of hydroxo complexes. The extraction of both metals decreases markedly in the presence of sulfate ions in the aqueous phase (a feature that is utilized in the stripping of the loaded hafnium with sulfuric acid), although the selectivity for hafnium over zirconium is simultaneously increased on account of the higher stability constants of the inextractable sulfato complexes of zirconium.298... 

The dioxygen complex shows oxygen transfer reactions characteristic of species containing coordinated peroxide (42), and, for example, we have isolated a sulfato complex from the reaction with S02 and a carbonato complex from a reaction with C02 in the presence of excess phosphine, and we have detected a peroxycarbonato species from the reaction with C02 (44). A reaction with H2 simply replaces the 02 to yield H2IrCl(PCy3)2, Complex 7 (44). 

Reactions and mass action - The reactions for the formation of the aluminium-sulfato complexes (Table 5.3) are... 

Figure 5.3 The relative proportions (a,) of monomeric hydroxy-aluminium species and aluminium-sulfato complexes as a function of pH. For the calculation ionic strength was fixed at 0.001 moldmT3 and activity corrections were made using the Davis equation.

Figure 4. Section of the pseudobinary phase diagram of the sulfuric acid SLP catalytic material. The data were taken from Ref. 16. The data points were derived from anomalies of the conductivity versus temperature curves of the respective mixtures. At the high compositional resolution and in the range of the global eutectic, the formation of a vanadate-sulfato complex causes the local maximum in the solidus curve. It is noted that extreme precision in the experimental procedures was necessary to derive this result illustrating the characteristic of fused systems that compound formation can well occur in the molten state.

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