Photochemical Synthesis and Characterization of a Uranyl Peroxide Triethylamine N-Oxide Dimer

A μ-peroxido-bis[di-triethylamine N-oxide-dichlorodioxouranium] complex with the formula [(UO2)2O2(ON(CH3)3)4Cl2] (complex 1) was synthesized photochemically from a reaction containing uranyl chloride, triethylamine, and H2O2. The photochemical breakdown of H2O2 yielded •OH radicals that reacted with triethylamine to form triethylamine N-oxide (TEAO) in situ, which subsequently coordinated to UO22+ cations in a monodentate fashion via the N-oxide functional groups. Structure determination using single crystal X-ray diffraction revealed that TEAO ligands also formed intermolecular and intramolecular hydrogen bonds with UO22+ and peroxide moieties, and the intermolecular H-bonding interactions displayed a temperature dependence with Oyl - - H – C and Oper - - H – C distances shortening at 100(2) K by ca. 0.1 Å. Additional coordination in the equatorial plane of complex 1 includes chloride ligands that are bound to each UO22+ cation in a trans orientation and an η2 : η2 μ2 peroxide (O22-) ligand connects the two UO22+ cations in a bent configuration. Raman spectroscopy data were collected on single crystals of 1 and peak fitting of these results allowed for assignments of peaks including C-N stretches for TEAO ligands bound to UO22+ cations at 696.8 cm-1, 717.8 cm-1, and 776.5 cm-1, which are redshifted by approximately 30 cm-1 when compared to free triethylamine. UO22+ ν1 and O22- ν1 stretches, U-Oper stretches, and notably, U-Cl stretches were all identified as well, with U-Cl modes at 198.9 cm-1 and 212.1 cm-1 substantially redshifted compared to the uranyl chloride starting material.