Dioxouranium(VI)-Carboxylate Complexes. Interaction of ${rm OU}_{2}^{2+}$ with 1,2,3,4,5,6-Benzenehexacarboxylate (Mellitate) in 0 ≤ I(NaCl a q ) ≤ 1.0 mol·L ?1

摘要

The formation constants of dioxouranium(VI)—1,2,3,4,5,6-benzenehexacarboxy- late [mellitate(6?)] complexes were determined in NaCl aqueous solutions at 0.1 ≤ I ≤ 1.0 mol·L?1 and t = 25 °C by ISE-[H+] glass-electrode potentiometry. The speciation model obtained at each ionic strength includes the following species: ML4?, MLH3?, MLH2 2 ?, MLH3 ?, M2L2?, MLOH5? and ML(OH)2 6? (M = UO2 2 + and L6? = mellitate). The ionic strength dependence of the protonation constants of mellitate and of the metal-ligand complexes was investigated using the SIT (Specific Ion Interaction Theory) approach. Formation constants at infinite dilution are [for the generic equilibrium $p{rm UO}_{rm 2}^{{rm 2 + }} + q({rm L}^{{rm 6} - }) + r{rm H}^{rm + }rightleftharpoons({rm UO}_{rm 2}^{{rm 2 +}})_p({rm L})_q {rm H}_r^{(2p - 6q + r)};,beta _{pqr}$ ]: log10 β 110 = 10.155, log10 β 111 = 16.084, log10 β 112 = 20.749, log10 β 113 = 24.038, log10 β 210 = 17.936, log10 β 11?1 = 2.327 and log10 β 11?2 = ?6.804. Simple linear relationships between the formation constants and the stoichiometric coefficients of reactants are reported. The sequestering capacity of mellitate towards UO2 2+ was quantified using a sigmoid Boltzman-type equation.