Dissociation kinetics of rare earth

A Comparison of the Dissociation Kinetics of Rare Earth Element Complexes with Synthetic Polyelectrolytes and Humic Acid... 

Here, we report on dissociation kinetic studies of the rare earth elements Sm(III) and Eu(III) from PAA and HA. The solution chemistry of both metals is essentially identical, and they are frequently used as analogs for trivalent actinide elements. We have studied the rare earth dissociation kinetics from different size fractions of PAA and HA using ion exchange and ligand exchange methods. The differences in metal labilities for complexes of the two polyelectrolytes and the effect of polyelectrolyte molecular weight on binding times are discussed in the context of possible polyion-cation interactions in these systems. 

Further kinetic results relevant to the ligand replacement reactions discussed in this section are those for dissociation of lanthanide(m)-cydta complexes. Nearly all the tervalent rare-earth cations were included in this investigation, along with the closely related complexes of scandium(ra) and yttrium(m). Dissociation rates vary with pH, but are unaffected by the addition of copper(n) ions. Thus there is no direct transfer of cydta from Ln + to Cu + in the manner of equation (7) (next section). The rate constants for the acid-dependent dissociation path show a large variation with the nature of the lanthanide cation they vary from 1291 mol s (at 25 °C, fjb = 0.1 mol 1 ) for lanthanum(ra) to 0.0171 mols for lutecium(m) the trend of rate constants is one of regular decrease as the ionic radius decreases. The rate constant of 0.019 1 mol s for dissociation of the scandium(in) complex is, however, much higher than would be expected from the ionic radius of Sc +. Activation parameters for dissociation of these cydta complexes are reported for the La", Gd, Dy Tm ", Lu , and Y compounds. ... 

Rare earth cryptates (table 5) are more stable than coronates and are highly kinetically inert towards dissociation in aqueous solutions. They can therefore be studied in water, but hydrolysis hinders their synthesis in this solvent. On the contrary, the preparation of unsolvated 1 1 complexes requires anhydrous conditions (Gansow and Triplett, 1981). The hydrated lanthanide salt solutions in... 

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