2:3 lanthanide complexes aqueous solution

Nitrogen donors usually form weak complexes with the lanthanides in aqueous solution. Sinha and Green 26) have measured the NMR spectra of complexes formed between 1,10-phenanthrohne and Ce(III), Pr(III), Nd(HI) and Eu(IH) in D2O. As the spectra were measured at room temperature, only time-average signals for the phenanthrohne protons were obtained. However, a plot of the shift of the protons as a function of the mole ratios of the hgand and metal ion (Fig. 2)... 

K.L. Nash and J.C. Sullivan, Kinetics of complexation and redox reactions of the lanthanides in aqueous solutions 347... 

An important and often overlooked aspect of complicated solution chemistry of salts other than inert electrolytes is fomiation of water soluble complex species involving products of dissolution of sparingly soluble materials (adsorbents). For instance, indirect spectroscopic evidence has been presented [1] that a silicate complex is the dominating soluble species of Eu (total Eu concentration of 10 mol dm ) in the presence of silicates (2.7x 10 mol Si dm ) over the pH range 6-8. The solubility of silica is about 10 mol dm, thus, water soluble silicate complexes can play an important role in the partition of Eu (and other trivalent lanthanides) between aqueous solution and silica. 

KINETICS OF COMPLEXATION AND REDOX REACTIONS OF THE LANTHANIDES IN AQUEOUS SOLUTIONS ... 

Nash, K.L., and J.C. Sullivan, 1991, Kinetics of complexation and redox reactions of the lanthanides in aqueous solutions, in Handbook on the Physics and Chemistry of Rare Earths, Vol. 15, eds K.A. Gschneidner Jr and L. Eyring (Elsevier, Amsterdam), pp. 347-391. 

Berkelium exhibits both the hi and iv oxidation states, as would be expected from the oxidation states displayed by its lanthanide counterpart, terbium. Bk(iii) is the most stable oxidation state in non-complexing aqueous solution. Bk(iv) is reasonably stable in solution, undoubtedly because of the stabilizing influence of the half-filled 5f electronic configuration. Bk(iii) and Bk(iv) exist in aqueous solution as the simple hydrated ions Bk (aq) and Bk (aq), respectively, unless complexed by ligands. Bk(iii) is green in most mineral acid solutions. Bk(iv) is yellow in HCl solution and is orange-yellow in H2SO4 solution. A discussion of the absorption spectra of berkelium ions in soluticm can be found in Section 10.4.3. 

It is well known, that in aqueous solutions the water molecules, which are in the inner coordination sphere of the complex, quench the lanthanide (Ln) luminescence in result of vibrations of the OH-groups (OH-oscillators). The use of D O instead of H O, the freezing of solution as well as the introduction of a second ligand to obtain a mixed-ligand complex leads to either partial or complete elimination of the H O influence. The same effect may be achieved by water molecules replacement from the inner and outer coordination sphere at the addition of organic solvents or when the molecule of Ln complex is introduced into the micelle of the surfactant. 

Because of the technical importance of solvent extraction, ion-exchange and precipitation processes for the actinides, a major part of their coordination chemistry has been concerned with aqueous solutions, particularly that involving uranium. It is, however, evident that the actinides as a whole have a much stronger tendency to form complexes than the lanthanides and, as a result of the wider range of available oxidation states, their coordination chemistry is more varied. 

Fig. 1.2 Standard enthalpy changes of (a) the complexing of lanthanide ions in aqueous solution by EDTA" ( left-hand axis) (b) the standard enthalpy change of reaction 2, the dichloride being a di-f...

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