Ligand‐Supported Facile Conversion of Uranyl(VI) into Uranium(IV) in Organic and Aqueous Media

Abstract

Reduction of uranyl(VI) to U V and to U IV is important in uranium environmental migration and remediation processes. The anaerobic reduction of a uranyl U VI complex supported by a picolinate ligand in both organic and aqueous media is presented. The [U VI O 2 (dpaea)] complex is readily converted into the cis-boroxide U IV species via diborane-mediated reductive functionalization in organic media. Remarkably, in aqueous media the uranyl(VI) complex is rapidly converted, by Na 2 S 2 O 4 , a reductant relevant for chemical remediation processes, into the stable uranyl(V) analogue, which is then slowly reduced to yield a waterinsoluble trinuclear U IV oxo-hydroxo cluster. This report provides the first example of direct conversion of a uranyl(VI) compound into a well-defined molecular U IV species in aqueous conditions. 1015 Lausanne (Switzerland)

Unveiling Role of Metals in Mononuclear Metal‐Complexes for Chemodosimetric Detection of S2− from aqueous medium: Experimental and DFT Corroboration with Real‐Field Application

“…Herein, in this system, DMSO acts a solvent as well as oxidant which oxidises the Co(II) to Co(III). Similar kind of role of DMSO has been previously reported by Wu et al [21] Co(II) donates an electron to the antibonding orbital of DMSO, as a result the oxidation state of the complex SN-1 changes from Co(II) to Co(III). Hence the formed complex becomes diamagnetic in nature.…”

Biological Reduction of a U(V)–Organic Ligand Complex

“…The two goals of this work were to confirm that U­(V) forms as a pathway intermediate in the presence of complexing ligands such as dpaea and to establish whether U­(V)–dpaea undergoes further biological reduction to U­(IV). We note that direct reduction of the U­(V)–dpaea complex by chemical reagents has been recently observed by some of the authors in both organic solvents and in water affording monometallic ([U IV (dpaea)­(OBpin) 2 (py)] and trimetallic ([Na­(H 2 O) 5 {U­(dpaea)} 3 (μ-O) 2 (μ–OH)­(μ 3 -SO 3 )]) complexes, respectively . Previously reported complexes of dpaea with uranium include U­(VI)–dpaea ([UO 2 (dpaea)]), U­(V)–dpaea ([K­(2.2.2.crypt)]­[UO 2 (dpaea)]), U­(IV)–dpaea (U­(dpaea) 2 ) , and the trinuclear uranium­(IV) μ-oxo/hydroxo bridged cluster [Na­(H 2 O) 5 {U­(dpaea)} 3 (μ-O) 2 (μ–OH)­(μ 3 -SO 3 )] obtained from the chemical reduction of U­(VI)– and U­(V)–dpaea in water.…”

“…The MtrCAB protein complex in S. oneidensis MR-1 spans potentials from 0 to −400 mV (against the standard hydrogen electrode (SHE)), 48 and therefore accesses a large range of redox substrates. The reduction potential of U(VI)–dpaea/U(V)–dpaea was −312 mV (SHE), 37 thus, the first reduction step of U(VI) to U(V), lies within the reduction potentials accessible to the MtrCAB complex. It suggests that a one-electron reduction of U(VI)–dpaea by MtrC/OmcA would be energetically favorable.…”

“…Regarding the second reduction step from U­(V)–dpaea to U­(IV), there is no reported redox potential for the U­(V)–dpaea/U­(IV) in aqueous medium. Indeed, the absence of a redox wave on the cyclic voltammogram of U­(V)–dpaea associated with the transition of U­(V) to U­(IV) may be explained by the slow kinetics of electron transfer or by significant structural rearrangements . However, dithionite, which is the reduced product in the sulfite/dithionite couple (HSO 3 2– /S 2 O 4 2– ), with an electrochemical potential of −660 mV against SHE at pH 7, was shown experimentally to reduce U­(V)–dpaea to U­(IV) in an aqueous solution buffered at pH 7 with HEPES .…”

“…We note that direct reduction of the U(V)–dpaea complex by chemical reagents has been recently observed by some of the authors in both organic solvents and in water affording monometallic ([U IV (dpaea)(OBpin) 2 (py)] and trimetallic ([Na(H 2 O) 5 {U(dpaea)} 3 (μ-O) 2 (μ–OH)(μ 3 -SO 3 )]) complexes, respectively. 37 Previously reported complexes of dpaea with uranium include U(VI)–dpaea ([UO 2 (dpaea)]), U(V)–dpaea ([K(2.2.2.crypt)][UO 2 (dpaea)]), U(IV)–dpaea (U(dpaea) 2 ) 38 , 37 and the trinuclear uranium(IV) μ-oxo/hydroxo bridged cluster [Na(H 2 O) 5 {U(dpaea)} 3 (μ-O) 2 (μ–OH)(μ 3 -SO 3 )] obtained from the chemical reduction of U(VI)– and U(V)–dpaea in water. The U(V)–dpaea complex is stable and soluble in water at pH 7, allowing for the persistence of the ordinarily transient pentavalent species.…”