On the stoichiometry and stability of americium(III) complexes with a hydrophilic SO3–Ph–BTP ligand, studied by liquid–liquid extraction

Abstract

1:1 and 1:2 complexes of americium(III) with a hydrophilic anionic SO3–Ph–BTP4− ligand were detected in acidic aqueous nitrate solutions by a solvent extraction method. The determined conditional stability constants of these complexes, logβ1 = 4.35 ± 0.07 and logβ2 = 7.67 ± 0.06, related to 1 M aqueous solutions, are much lower than the literature values for the analogous curium species, determined by TRLFS in very dilute aqueous solutions. There is also no evidence for the existence of the 1:3 Am3+ complex similar to the reported curium(III) complex. A hypothesis has been formulated to explain these discrepancies. It suggests the necessity to carefully check the equilibria in each phase of solvent extraction systems containing two competing ligands—lipophilic and hydrophilic.

New trends in the reprocessing of spent nuclear fuel. Separation of minor actinides by solvent extraction

“…The existence of such mixed-ligand complexes of the lightest lanthanides had already been postulated by Pacary et al who modeled the EXAm system [55]. These suggestions well correspond to our recent hypothesis on the formation of the extractable lipophilic heteroleptic Am III complexes with TODGA and SO 3 -Ph-BTP 4-, which we formulated independently [38].…”

“…In order to understand why the 1:3 complex had not been observed in the solvent extraction system, we determined the number and stoichiometry of the Am 3+ -SO 3 -Ph-BTP 4complexes in the acidic (HNO 3 ) aqueous phase of a two-phase system, and calculated the stability constants of the complexes in the presence of two competing ligands: hydrophilic SO 3 -Ph-BTP 4in the aqueous phase and lipophilic TODGA in the organic phase of the system studied. Only two Am 3+ complexes (1:1 and 1:2) were found in the broad range of SO 3 -Ph-BTP 4concentrations studied, moreover, of distinctly lower stability constants than those of the respective Cm 3+ complexes which had been determined in the single aqueous phase (without TODGA) [38]. Because of that, we have presented a hypothesis that lipophilic heteroleptic complexes can be formed in the two-phase system, for example [Am(TODGA) 2 (SO 3 -Ph-BTP)]extractable as an ion pair with protonated extractant (TODGA•H + ) from the acidic aqueous phase [38].…”

“…Only two Am 3+ complexes (1:1 and 1:2) were found in the broad range of SO 3 -Ph-BTP 4concentrations studied, moreover, of distinctly lower stability constants than those of the respective Cm 3+ complexes which had been determined in the single aqueous phase (without TODGA) [38]. Because of that, we have presented a hypothesis that lipophilic heteroleptic complexes can be formed in the two-phase system, for example [Am(TODGA) 2 (SO 3 -Ph-BTP)]extractable as an ion pair with protonated extractant (TODGA•H + ) from the acidic aqueous phase [38]. The search of such hypothetical species has already been started.…”

Determination of formation constants of uranyl(VI) complexes with a hydrophilic SO3-Ph-BTP ligand, using liquid-liquid extraction

“…On the contrary, our further studies on the complexation of Am 3+ with SO 3 -Ph-BTP 4resulted in the similar 'best fi t' adjustment of the [L 4-] values at logK H,1 = 0.5 [21], i.e. the value equal to that determined by spectrophotometry [19].…”

Do An(iii) and Ln(iii) ions form heteroleptic complexes with diglycolamide and hydrophilic BT(B)P ligands in solvent extraction systems? A spectroscopic and DFT study

“…A discrepancy between the results of the spectroscopic and solvent extraction studies was observed not only in the stoichiometries of the M(III)-SO 3 -Ph-BTP complexes but also in their stabilities. In a previous solvent extraction study on the complexation of Am(III) with SO 3 -Ph-BTP 4À only two complexes, 1 : 1 and 1 : 2, were found, 34 with conditional stability constants lower by more than an order of magnitude than the corresponding values determined spectroscopically for the corresponding complexes of Cm(III). 15 Similar observations were made for the related tetradentate chelators SO 3 -Ph-BTBP and SO 3 -Ph-BTPhen (Scheme 1).…”