The highest nuclearity 5f-metal/oxime cluster: Synthesis, structure and properties of a tetranuclear uranyl compound

The synthetic investigation of the UO 2 (NO 3 ) 2 . 6H 2 O/LH 2 /Et 3 N reaction system in MeCN has provided access to the tetranuclear compound (HNEt 3 ) 2 [(UO 2 ) 4 O 2 (L) 2 (LH) 2 ] ( 1 ) in moderate yield; LH 2 is o -vanillin oxime. The four trans- {U VI O 2 } 2+ in 1 are held together by two μ 3 -oxido groups, two 2.1101 (Harris notation) L 2− ligands and two 2.2101 HL − ones. The metal topology is nearly rhombic, and the {U VI 4 (μ 3 -Ο 2− ) 2 } unit has a “butterfly” arrangement; the core of the tetranuclear anion is {U 4 (μ 3 -O) 2 (μ 2 -OR) 2 }. The O=U=O groups are moderately bent [176.8(1) and 175.1(1) °]. The solid compound has been characterized by IR, Raman and UV/VIS (diffuse reflectance) spectroscopies, and the data are discussed in terms of the structural features of 1 . The structure of the compound is retained in DMSO (and probably in DMF) solution as judged by molar conductivity data, 1 H NMR and UV/VIS spectra. The compound is redox-active in DMF displaying a metal-centered one-electron, quasi-reversible reduction at each uranyl unit. Cluster 1 exhibits a satisfactory photocatalytic activity in the degradation of methylene blue under UV light in aqueous media. Based on literature reports, a simplified mechanistic scheme for the photocatalysis is proposed.