Coordination and separation studies of the uranyl ion with iso-butyramide based ligands: Synthesis and structures of [UO2(NO3)2(iC3H7CON{iC4H9}2)2] and [UO2(C6H5COCHCOC6H5)2(iC3H7CON{iC3H7}2)]
Graphical abstract
Coordination studies of iso-butyramide based ligands show that they form 2:1 and 1:1 compounds respectively with the uranyl nitrate and uranyl bis(β-diketonates). These ligands act as monodentate ligand and bond through the carbamoyl oxygen atom to the uranyl moiety. These ligands can selectively precipitate uranyl ion from the mixture containing other ions such as thorium(IV) and lanthanum(III).
Introduction
Actinide coordination chemistry is very important for the development of new technology concerning the safe processing and storage of irradiated nuclear fuel materials [1], [2], [3]. The selective separation of uranium-233 from the mixture of thorium and other fission products is an important step [4a] in the advanced heavy water reactor (AHWR) technology [4b] of the Indian atomic energy program, where upon the thorium oxide is used as a fuel material. In recent years, incinerable organic amide based extractants have proved to be of particular interest in the process chemistry of lanthanides and actinides from the nitric acid medium [5]. It is reported that the N,N′-2,ethylhexyl iso-butyramide shows selective extraction property for the uranium(VI) ion from a mixture containing thorium(IV) or plutonium(IV) ion [6]. The solvent extraction method needs many steps such as: extraction, stripping, precipitation and purification during the reprocessing of fuel materials. The neutral N-cyclohexyl,2-pyrrolidone ligand shows selective precipitation of uranium(VI) ion (up to 68%) from the mixture containing various other ions [7] and with this ligand only two steps are required namely precipitation and purification. The selectivity of N-cyclohexyl,2-pyrrolidone ligand was explained on the basis of a strong complexing nature of this ligand towards the uranyl nitrate compared to those of other metal nitrate ions. We have reported recently that iso-butyramide based amide ligands show an excellent coordination property towards the uranyl group and form air and moisture stable halide and thiolato complexes [8], [9]. The stability of these complexes was explained on the basis of very strong bonding between the amide and uranyl group. The observed bond distances in these complexes are much shorter in length compared to those of any of the uranyl-amide [10], [11], [12], uranyl-phosphine oxide [13], [14], [15], [16], [17] and uranyl-pyrrolidone [18], [19] complexes reported. The strong complexing ability of the iso-butyramide based ligand promoted us to study their complexing behavior towards uranyl nitrate, thorium nitrate, lanthanum nitrate and uranyl bis(β-diketonate) to investigate whether it was feasible to use these ligands for separation purposes and the results of these studies are reported herein.
Section snippets
General considerations
All the starting materials and other chemicals were reagent grade and were used as received. All the amides [8] and uranyl bis(β-diketonates) [20] were prepared according to the reported methods. FTIR spectra were obtained on a JASCO-610 FTIR spectrometer and the samples were mounted as a Nujol mull. The 1H NMR spectra in CDCl3, on a Brucker 500 MHz spectrometer and the peak positions are calibrated with respect to the internal residual solvent peaks. Elemental analyses were performed by the
Complexation study of iso-butyramide ligands with the uranyl nitrate
The complexing ability of iC3H7CON(iC3H7)2, iC3H7CON(C4H9)2 and iC3H7CON(iC4H9)2 with uranyl nitrate was studied by using elemental analysis, IR and NMR spectroscopic techniques. The reaction of [UO2(NO3)2 · 6H2O] with the iso-butyramide ligands yielded the compounds 1–3. The C, H and N analysis revealed that the ratio of ligand to uranyl nitrate is 1:2 in all these compounds. The IR spectra of 1–3 show that the water molecules from the starting compound [UO2(NO3)2 · 6H2O] are completely replaced
Conclusions
Studies on the coordination ability of the iso-butyramide based ligands with the uranyl(VI) nitrate show that the ligands act as monodentate ligand and form 1:2 complexes. The studies further show that the ligands are un-reactive towards the thorium(IV) and lanthanum(III) nitrates. Preliminary precipitation studies show that the U(VI) can be selectively separated as an uranyl nitrate amide complex from the solution containing the mixture of U(VI), Th(IV) and La(III) ions. TG/DTA experiments
Supplementary material
X-ray crystallographic files in CIF format for 3 and 8, IR, 1H NMR spectra and TG/DTA of 3 and TXRF spectra of the Th, U and La mixture, uranyl nitrate precipitate and the supernatant are deposited to the editor as supporting information. Crystallographic data may be obtained from the Cambridge Crystallographic Data Center, by quoting the reference number CCDC: 680831 and 680832. Copies of this information may be obtained free of charge from The Director, CCDC, 12, Union Road, Cambridge,
Acknowledgements
We wish to thank, the Head, Analytical Chemistry Division, BARC, for carbon, hydrogen and nitrogen analysis, the Head, National NMR facilities, TIFR, Mumbai for NMR spectra, Kum. S. Dhara for TXRF, Dr. N.K. Kulkarni for TG/DTA, Dr. S.K. Aggarwal, Head, Fuel Chemistry Division and Dr. K.L. Ramakumar, Head, Radioanalytical Chemistry Division for their support. We also wish to thank the EPSRC (UK) and the University of Reading for funds for the Oxford Diffraction CCD system.
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