The first acidification step of the tris(carbonato)dioxouranate(VI) ion, UO2(CO3)34-

Abstract

Bz0s(en)H20]2+"isn + isn -*• (2)In other words we would need to invoke an activated complex with two entering ligands, one of them acting to labilize the Os(II) center but not disposed to enter the coordination sphere. It seems prudent to defer further speculation until the system and related ones have been more thoroughly explored. The datum at the lowest isonicotinamide concentration can be taken as being the most directly related to the specific rate for reaction 1. The value of specific rate calculated from it is 0.9 X 10"5 M"1 s"1, to be compared to 1.3 X 10"3 M"1 s"1 for Cl" as entering group. A factor of 100 is not unreasonable as resulting from the difference in charge between the two entering groups, and in this respect at least, our observations are not out of line.In the matter of substitution lability, a remarkable qualitative result is the rapidity with which the CO complex is formed. Referring back to the procedure which was followed, when CO is present at atmospheric pressure-corresponding perhaps to 10"3 M in methanol solution-reaction is largely complete in 5 min. Even on the assumption that the half-life is 5 min, the second-order specific rate is calculated as ca. 3, to be compared to 0.9 X 10"5 for isn. A large factor directly involved in the rate difference is that, in the CO case, the reactant species is BzOsC12CH3OH, and the labilizing effect of the two chloride ions is being exploited in the facile substitution. The labilizing effect of NH2CH2C02" as compared to en has already been noted.

An Energy Dispersive X‐ray Diffraction Study of Dioxouranium(VI) in 1 M Lithium Citrate

“…The uranyl perchlorate stock solution was prepared and standardized, with an accuracy of 0.3%, as suggested in ref. [1] starting from UO 2 (NO 3 ) 2 ·6H 2 O (Fluka p. a.).…”

“…Sodium perchlorate was prepared and standardized as described elsewhere. [1] The pH of solution B was 5.10Ϯ0.02 at 18°C. It was measured with a Metrohm 691 pH-meter equipped with a 6.0232.100 glass combined electrode (Metrohm); the electrode was calibrated with IUPAC pH standards.…”

“…Besides the well-established importance of their mononuclear complexes, with a unique or with different ligands, the formation of polynuclear complexes may substantially influence the speciation involved under specific thermodynamic conditions typical of the environment, for instance by enhancing the solubility of a solid phase. In connection with this, the most instructive example is probably represented by the [(UO 2 ) 3 (CO 3 ) 6 ] 6Ϫ complex, which has been since the determination of its formation constant through potentiometry, [1] extensively investigated by a large number of different techniques. [2,3,4] Similar investigations are still performed, first potentiometrically and then by other methods, on the complexes between UO 2 2ϩ and acetate, UO 2 2ϩ and oxalate, and UO 2 2ϩ with ligands containing at least one carboxylic group.…”

Effects of the mycorrhizal fungus Glomus intraradices on uranium uptake and accumulation by Medicago truncatula L. from uranium-contaminated soil

“…and as soluble carbonate complexes (Ciavatta et al, 1981;Duff and Amrhein, 1996;Grenthe et al, 1992;Langmuir, 1978). Between pH 4.0 and 7.5, the pH range of most soils, U(VI) exists primarily in hydrolyzed forms (Meinrath et al, 1996).…”

On the hydrolysis of the Dysprosium(III) ion

“…The lanthanide content was determined, with an accuracy of ±0.2%, trough EDTA titrations, both volumetric, using xylenol orange as indicator, and conductometric. Sodium perchlorate stock solutions were prepared and titrated (with an accuracy of ±0.05%) as reported by Ciavatta et al (1981). The perchloric acid excess was determined through coulometric titrations.…”