Di‐μ‐acetato Diuranyl(VI) Complexes with N‐(2‐pyridyl)‐N′‐(5‐R‐salicylidene)hydrazines: Syntheses, Structures, Properties and Extraction Studies

Abstract

AbstractReactions of equimolar amounts of UO2(OAc)2⋅2H2O and N‐(2‐pyridyl)‐N′‐(5‐R‐salicylidene)hydrazines (HLn; n=1–3 for R = H, Me, and OMe, respectively) in methanol produced [(UO2)2(μ‐OAc)2(Ln)2] (1‐3 for n=1–3) in ∼70% yields. Elemental analysis, various spectroscopic, and electrochemical measurements were used to characterize 1‐3. X‐ray crystal structures revealed an 8‐membered U(OCO)2U ring with a chair conformation and pentagonal‐bipyramidal UN2O5 coordination spheres in each of 1‐3. The N,N,O‐donor (Ln)‐ and the two O‐atoms of the two bridging (OAc)‐ form the pentagonal plane around the U‐atom of trans‐(UO2)2+. Intermolecular H‐bonding assisted self‐assembly of the complexes lead to 1‐ and 2‐dimensional supramolecular structures. Infrared (IR) and proton nuclear magnetic resonance (1H NMR) spectra of 1‐3 are consistent with their molecular structures. The electronic spectra showed four strong absorption bands in the range 466‐288 nm. The complexes undergo two irreversible reductions near ‐0.65 and ‐0.88 V (vs. Ag/AgCl). Time‐dependent density functional theory (TD‐DFT) calculations suggest that a ligand centered transition causes the highest energy absorption band, while, the remaining three are ligand‐to‐metal charge transfer (LMCT) bands and the two successive reductions are due to U(VI)‐U(VI) → U(V)‐U(VI) → U(V)‐U(V) processes. A maximum extraction of 98% of trans‐(UO2)2+ from the aqueous layer was observed in two‐phase extraction studies.