Potentiometric and UV-Visible Spectrophotometric Studies of the Stability of Thorium(IV) Complexes with (o-Hydroxyphenyl) Mono- and Di-Methylenephosphonic Acids
Résumé
Protometric studies were performed in aqueous solutions at 25 • C and 0.1 mol•dm −3 ionic strength (NaClO 4) to determine the complexing abilities of eight (ohydroxy-phenyl) mono-and di-methylenephosphonic acids (differently substituted by chromophoric or auxochromic groups) towards thorium(IV). The number, the nature of the species present in solution, their overall stability constants over a broad acidity range and their individual electronic spectra, as resolved by computation, have been determined by potentiometry and UV-visible spectrophotometry. The formation of 1:1 species, partially protonated MLH x and totally deprotonated [ML], as well as hydroxo species-mononuclear ML(OH) x and dinuclear M 2 L(OH) x is reported with thorium(IV). The results show that the complexing power, which is not very different in the lanthanide series, is much higher for thorium(IV). The ratio Th 4+ /Eu 3+ reaches eight log 10 units with some of the ligands.
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