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

Abstract

Reactions 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.

A Diuranyl(VI) Complex and Its Application in Electrocatalytic and Photocatalytic Hydrogen Evolution from Neutral Aqueous Medium

“…The four-membered bridging U 2 O 2 unit is perfectly planar, and the U···U distance and U–O–U and O–U–O angles are 3.9067(5) Å and 111.2(2) and 68.8(2)°, respectively. The U(1)–O(1) and U(1)–O(1′) bond lengths are comparable with the uranium­(VI) to bridging alkoxide O distances observed before. , Overall the UO, U–O­(phenolate), U–N­(azomethine), and U–N­(amine) bond lengths in [(UO 2 ) 2 (μ-L) 2 ] are within the ranges reported for uranium­(VI) complexes having similar coordinating atoms. − …”

“…In the DPV, the reduction peaks are relatively well resolved and they appear at −0.56 and −0.86 V with comparable peak currents. Complexes of trans -uranyl­(VI) complexes with Schiff bases are known to display U­(VI) → U­(V) reduction in a similar potential range. , Thus the two reductions observed for the present complex are attributed to U­(VI)–U­(VI) → U­(V)–U­(VI) → U­(V)–U­(V) processes.…”

Chiral Diuranyl(VI) Complexes and Their Catecholase Activities: Experimental and Theoretical Insights

“…Each complex displays two successive irreversible cathodic responses. The E pc of the first response is within −0.77 to −0.82 V, and that of the second response is in the range of −1.16 to −1.24 V. The peak currents of both responses are very similar and comparable with the peal currents of the Fc + /Fc couple and other known one electron redox processes under identical conditions [12c,e,13c] . The reduction potentials of the present complexes are within the metal centered reduction potential range reported for trans ‐uranyl(VI) complexes with Schiff base ligands [10c,12a,c,e,f] .…”

“…Thus the group of bands at higher energy and the strong band at 1642 cm −1 observed for 3 and 4 are assigned to the C−H and C=O stretching bands, respectively of the metal coordinated Me 2 NCHO. A strong band appeared in the range 1605–1620 cm −1 for all the complexes is attributed to the metal coordinated C=N [10c,12a,c,e,f,13a,c,16] . All four spectra display the typical very strong band at ∼894 cm −1 due to the asymmetric stretching vibration of the trans ‐uranyl(VI) moiety [10a,c,12a,c–f] …”

“…A strong band appeared in the range 1605–1620 cm −1 for all the complexes is attributed to the metal coordinated C=N [10c,12a,c,e,f,13a,c,16] . All four spectra display the typical very strong band at ∼894 cm −1 due to the asymmetric stretching vibration of the trans ‐uranyl(VI) moiety [10a,c,12a,c–f] …”