Enhancement of hydrolysis through the formation of mixed hetero-metal species.
In order to analyze the formation of hetero-metal polynuclear hydrolytic species, in this paper, we reported some results of an investigation (at I = 0.16molL(-1) in NaNO(3), at t = 25 degrees C by potentiometry, ISE-H(+), glass electrode) on the hydrolysis of several mixtures (in different ratios) of two couples of cations: dioxouranium(VI)/copper(II) and dioxouranium(VI)/diethyltin(IV). The elevated total concentrations of cations 0.005 </= SigmaC(M) molL(-1) </= 0.05) adopted in these measurements induced us to study again the hydrolysis of uranyl, for which no suitable literature data are available in these particular experimental conditions. All measurements were performed by two different operators, using completely independent instruments and reagents. Many different speciation models were considered in the calculations, including the simultaneous refinement of homo- and hetero-metal species, and a statistical analysis of obtained results was proposed too. Main results can be summarized as follows: [Formula: see text] and Cu(2+) form three hetero-metal polynuclear hydrolytic species [(UO(2))Cu(OH)(3+), (UO(2))Cu [Formula: see text] and (UO(2))(2)Cu [Formula: see text] , with log beta(pqr) = -2.93 +/- 0.01, -7.34 +/- 0.03 and -13.78 +/- 0.03, respectively], all those common to their simple speciation without the other cation; [Formula: see text] and (C(2)H(5))(2)Sn(2+) form seven mixed hydrolytic species [(UO(2))(DET)(OH)(3+), (UO(2))(DET) [Formula: see text] , (UO(2))(2)(DET) [Formula: see text] , (UO(2))(DET)(2) [Formula: see text] , (UO(2))(2)(DET) [Formula: see text] , (UO(2))(DET)(2) [Formula: see text] and (UO(2))(2)(DET) [Formula: see text] , with log beta(pqr) = -2.5 +/- 0.2, -4.74 +/- 0.02, -10.70 +/- 0.06, -10.34 +/- 0.03, -15.70 +/- 0.06, -15.58 +/- 0.06 and -27.9 +/- 0.1, respectively] that are of the same kind of those formed by uranyl; formation of mixed hydrolytic species causes a significant enhancement of the percentage of hydrolyzed metal cations, modifying the solubility and, therefore, the bioavailability of these cations. We also determined, for dioxouranium(VI)/copper(II) system, the corresponding complex formation enthalpies and entropies by direct calorimetric measurements. We obtained DeltaH(112) = 47.9 +/- 0.6 and DeltaH(214) = 92.9 +/- 0.5kJmol(-1), TDeltaS(112) = 6 +/- 1 and TDeltaS(214) = 14 +/- 1kJmol(-1) (+/-S.D.), respectively, for the formation of (UO(2))(Cu) [Formula: see text] and (UO(2))(2)(Cu) [Formula: see text] species (according to reaction 2). We also calculated the single enthalpic and entropic contributes to the extra-stability that these species show with respect to the corresponding homo polynuclear ones.
Crea
Francesco
F
Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Salita Sperone, 31, I-98166 Messina (Vill. S. Agata), Italy.
Milea
Demetrio
D
Sammartano
Silvio
S