The
complexation of uranium(VI) [U(VI)] with dipicolinic acid was
revisited with respect to the missing protonated complex species existing
in acidic solutions. For the first time, the presence of the protonated
complex, UO2HL+, in aqueous solutions was confirmed
and the stability constant was determined by fluorescence spectroscopy.
Considering the protonated species, which was missing in previous
investigations, the overestimated stability constants of the two known
complexes, UO2L and UO2L2
2–, were carefully reevaluated with potentiometry using N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid as a competing
ligand. While a single crystal of the solid compound UO2(HL)2(H2O)4 with two monoprotonated
HL– bonding UO2
2+ in a tridentate
mode was successfully grown from aqueous solutions, the corresponding
complex species UO2(HL)2(aq) could not yet be
clearly identified and characterized.
As the primary functional groups of amidoximed sorbent for uranium recovery from seawater, di(amidoxime) ligands can be cyclized in situ to different ligands in the presence of Cu(II)/Ni(II) and different...
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