Dioxidouranium(IV) complexes with Schiff bases possessing an ONO donor set: Synthetic, structural and spectroscopic studies

Abstract

Tridentate Schiff bases derived from the condensation of salicylaldehyde and o-aminophenol or its derivatives have rarely been used in 5f-metal chemistry. Synthetic investigations of the UO2(O2CMe)2·2H2O/4MesaphH2 and UO2(O2CMe)2·2H2O/4ClsaphH2 systems, where 4MesaphH2 is N-salicylidene-4-methyl-o-aminophenol and 4ClsaphH2 is N-salicylidene-4-chloro-o-aminophenol, have provided access to the complexes [(UO2)2(4Mesaph)2(EtOH)2] (1) and [(UO2)2(4Clsaph)2(EtOH)2] (2), respectively, in moderate to good yields. The structures of the isomorphous complexes have been determined by single-crystal X-ray crystallography. In the dinuclear molecules, the two UVI atoms are bridged by two phenoxido oxygen atoms that belong to the methyliminophenolate (1) or chloroiminophenolate (2) parts of the two doubly deprotonated 2.121 ligands. Each UVI center is surrounded by one imine nitrogen and six oxygen atoms in a distorted pentagonal bipyramidal geometry, in which the two uranyl oxido atoms occupy the axial positions. H-bonding interactions build the 3D architectures of the compounds; the H-bond donors are the coordinated ethanol oxygen and aromatic carbon atoms, while the acceptors are the terminal oxygen atoms of the salicylaldehyde parts of the ligands and one of the uranyl oxygen atoms. IR data are discussed in terms of the coordination modes of the ligands. 1H NMR spectra in DMSO‑d6 provide evidence that the structures of the complexes are retained in solution. Upon maximum excitation at 445 nm, a green light emission with a maximum at 563 nm has been recorded for solid 2 at room temperature.