The present work reports the hydrolysis of ions of the series of lanthanides (III) and actinide (IV) elements in dilute aqueous solutions. It has been systematically examined in the presence of sodium perchlorate, which has been used for maintaining the solution at constant ionic strength. The number, the nature of the species in solution and their hydrolysis constants logb 10i for all ions at I = 0.1 mol dm -3 and at 25°C were determined by different softwares: Superquad and Sirko_P. A pH-potentiometric method was used with glass electrodes to determine the equilibrium constants K i :n+ represents Ce 3+ , Pr 3+ , Nd 3+ , Eu 3+ , Sm 3+ and Th 4+ ions. For the lanthanides, hydrolysis increases with the increase of the atomic number and the contraction of the ionic radius. The Th 4+ ion undergoes significant hydrolysis. To cite this article: E. Bentouhami et al., C. R. Chimie 7 (2004). RésuméCette étude concerne l'hydrolyse des ions de la série lanthanides (III) et du thorium (IV) ; elle a été effectuée en présence de perchlorate de sodium, utilisé pour maintenir constante la force ionique des solutions I, égale à 0,1 mol dm -3 . Le nombre et la nature des espèces en solutions, ainsi que leurs constantes d'hydrolyse logb 10i , ont été déterminées à 25°C à l'aide de différents softwares de calculs, à savoir, Superquad et Sirko_P. Une méthode potentiométrique est utilisée sur électrode de verre pour déterminer les constantes d'équilibres K i :OH) (n−1)+ + H + où M n+ représente les ions Ce 3+ , Pr 3+ , Nd 3+ , Eu 3+ , Sm 3+ et Th 4+ . Pour les lanthanides, l'hydrolyse augmente avec le numéro atomique et la diminution du rayon atomique. On montre que l'ion Th 4+ subit l'hydrolyse de manière significative. Pour citer cet article : E. Bentouhami et al., C. R. Chimie 7 (2004).

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Co n chloro complexes were studied in MeOH at 25 ~ and at constant ionic strength of 1 tool dm 3. Formation of three complexes is postulated for which the overall stability constants are calculated: log/~1=1.2, log/~2 = 1.7 and log fi3 = 1.4. The electronic spectra and the formation curves of the identified species are presented for the first time in this medium. The results are compared with those obtained in other alcohols and increasing stability with increasing molecular weight of the solvents is established. Further comparative study showed that the maximum stability of the chloro complexes is found with the Cu n ion as the central atom. This confirms the IrvingWilliams order of stabilities for the first transition metal complexes in this alcoholic medium and the result is explained in terms of the second ionization potential of the elements.

A spectrophotometric study of the copper(I1) chlorides and the copper(I1) bromides in anhydrous methanol was carried out at 25 "C and at constant ionic strength (1 mo1.L-I). A matrix rank treatment of the experimental data followed by the testing of different theoretical models confirmed the presence of four mononuclear complexes for both systems, viz. C u X ' , CuX2, CuX3-, and CuXz-. Overall stability constants calculated for the chlorocuprates are PI = 2.8 X lo2, b2 = 1.6 X IO4, 8, = 2.3 X los, and P4 = 4.5 X lo5 and for the bromocuprates are PI = 5.2 X lo', P2 = 3.9 X IO5, P3 = 2.0 X lo6, and b4 = 2.1 X lo6. Individual electronic spectra of all species in methanol are reported for the first time. In this solvent the tetracoordinated chloro complex exhibits a calculated absorption maximum in the near-IR region consistent with a square-planar structure, in contrast to the structure in the solid state, while for the tetrabromocuprate the structure of a flattened tetrahedron is confirmed. IntroductionThe copper( 11) chlorides have been extensively studied in aqueous and nonaqueous solutions, as have the bromide complexes, although to a lesser extent. The results of studies carried out at constant ionic strength are definitely divergent, and few allusions have been made to the more highly substituted halide complexes.