The effect of iron binding on uranyl(v) stability.

ABSTRACT: Here we report the effect of UO2 +···Fe2+ cation-cation interactions on the redox properties of uranyl(v) complexes and on their stability with respect to proton induced disproportionation. The tripodal heptadentate Schiff base trensal3- ligand allowed the synthesis and characterization of the uranyl(vi) complexes [UO2(trensal)K], 1 and [UO2(Htrensal)], 2 and of uranyl(v) complexes presenting UO2 +···K+ or UO2 +···Fe2+ cation-cation interactions ([UO2(trensal)K]K, 3, [UO2(trensal)] [K(2.2.2crypt)][K(2.2.2crypt)], 4, [UO2(trensal)Fe(py)3], 6). The uranyl(v) complexes show similar stability in pyridine solution, but the presence of Fe2+ bound to the uranyl(v) oxygen leads to increased stability with respect to proton induced disproportionation through the formation of a stable Fe2+-UO2 +-U4+ intermediate ([UO2(trensal)Fe(py)3U(trensal)]I, 7) upon addition of 2 eq. of PyHCl to 6. The addition of 2 eq. of PyHCl to 3 results in the immediate formation of U(iv) and UO2 2+ compounds. The presence of an additional UO2 + bound Fe2+ in [(UO2(trensal)Fe(py)3)2Fe(py)3]I2, 8, does not lead to increased stability. Redox reactivity and cyclic voltammetry studies also show an increased range of stability of the uranyl(v) species in the presence of Fe2+ with respect both to oxidation and reduction reactions, while the presence of a proton in complex 2 results in a smaller stability range for the uranyl(v) species. Cyclic voltammetry studies also show that the presence of a Fe2+ cation bound through one trensal3- arm in the trinuclear complex [{UO2(trensal)}2Fe], 5 does not lead to increased redox stability of the uranyl(v) showing the important role of UO2 +···Fe2+ cation-cation interactions in increasing the stability of uranyl(v). These results provide an important insight into the role that iron binding may play in stabilizing uranyl(v) compounds in the environmental mineral-mediated reduction of uranium(vi).

SUBMITTER: Faizova R 

PROVIDER: S-EPMC6179087 | biostudies-other | 2018 Oct

REPOSITORIES: biostudies-other