Uranyl-Promoted Peroxide Generation: Synthesis and Characterization of Three Uranyl Peroxo [(UO₂)₂(O₂)] Complexes

Abstract

Three novel uranyl(VI) peroxide complexes, [(UO2)2(CH3COO)2(O2)(C10H8N2)] (1), [(UO2)2(CH3COO)2(O2)(C12H12N2)] (2), and [(UO2)3(CH3COO)4(O2)(C15H11N3)2] (3), have been synthesized and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and luminescence spectroscopy. Each of these structures feature a [(UO2)2(O2)] dimer with additional coordination by acetate, 2,2'-bipyridine (BPY), 5,5'-dimethyl-2,2'-bipyridine (MeBPY), or 2,2':6,2″-terpyridine (TPY). Compound 3 consists of an additional uranyl unit functionalized with a TPY donor ligand. The presence of the peroxo ligand in 1-3 is due to in situ generation of peroxide when preparative solutions of 1-3 were exposed to ambient light and/or sunlight.

Unprecedented Catalytic Behavior of Uranyl(VI) Compounds in Chemical Reactions

“…[ 74 ] The possibility of generating aldehyde and carboxylic acid products from the oxidation of methanol by H 2 O 2 under the photocatalysis of uranyl species has been reported. [ 75 ]…”

Uranyl Ion Complexes of Polycarboxylates: Steps towards Isolated Photoactive Cavities

“…It also has features found in many other uranyl complexes in that the carboxylate groups are bound as κ 2 O,O' chelates and the peroxide ligands act as bridges to produce convergent U(O 2 )U units. The adventitious presence of peroxide in the complex is not an unusual observation in uranyl ion coordination chemistry and detailed studies [57,58] have led to its rationalisation as a result of photochemical reduction of uranyl ion by water or organic substrates (such as methanol) to give U(V), which subsequently reacts with atmospheric oxygen to give peroxide. The bent form of the U(O 2 )U unit is favourable for the formation of a closed species and this effect is spectacularly exemplified in the extraordinary family of cages formed by uranyl ion in the presence of peroxide ion and various co-ligands such as oxide, hydroxide, nitrate, phosphate and other simple oxyanions, a family known to extend up to a multi-compartmental cage built from 124 uranyl units [59,60].…”

“…The bent form of the U(O 2 )U unit is favourable for the formation of a closed species and this effect is spectacularly exemplified in the extraordinary family of cages formed by uranyl ion in the presence of peroxide ion and various co-ligands such as oxide, hydroxide, nitrate, phosphate and other simple oxyanions, a family known to extend up to a multi-compartmental cage built from 124 uranyl units [59,60]. The presence of bound peroxide on uranyl ion, however, has the unfortunate consequence that uranyl ion emission, with its characteristic multiple vibronic components [21,61], is quenched, though ligand-centred emission is observed in some cases [58,62]. Thus, the [(UO2)8(L)8(O2)4] 8− cavity must be considered unsuitable for photocatalysed oxidation reactions involving the excited UO2 2+ ion.…”

Photoinduced Transformation of Uranyl Nitrate Crown Ether Compounds

“…Formation of the peroxide radical typically occurs in the presence of an organic substrate and requires dissolved O 2 gas to be present in the solution [7] . In this case, the non‐radiative decay process occurs through excitation of the triplet state O 2 to form the superoxide radical [7d] . This species can interact with protons present in the solvent to form the hydrogen peroxide molecule [7d] .…”

“…In this case, the non‐radiative decay process occurs through excitation of the triplet state O 2 to form the superoxide radical [7d] . This species can interact with protons present in the solvent to form the hydrogen peroxide molecule [7d] . The uranyl cation will strongly bind to peroxide through the equatorial plane to create uranyl peroxo coordination complexes in solution.…”