ABSTRACT
The selective extraction of uranium by N-octylcalix[4]azacrown (NOCAC) and N-ethylhexylcalix[4]azacrown (NEHCAC) was investigated. The ligands were synthesised in three steps through the functionalisation of t-butyl calix[4]arene at the distal-1,3-positions of the lower rim with ethyl acetate groups followed by cyclisation with (imino)bis(ethane-2,1-diyl)diamide. A detailed investigation on the effect of various parameters, such as the aqueous phase acidity (sulfuric acid), the ionic strength, and ligand concentration, on the extraction of uranium(vi) has been conducted. The effect of the H2SO4 concentration has been studied from 0.02 to 3 M. Preliminary studies carried out on NOCAC in dodecane/octanol diluents showed that the uranium extraction from sulfuric acid is more efficient at a low H2SO4 concentrations. The stoichiometry of complexation was estimated from the slope method, NMR titration, and electrospray ionisation-mass spectrometry analysis. Both ligands were found to be highly selective for uranium(vi) over other competitive cations present in a simulated leach solution containing seven competitive cations. The successful recovery of the uranium from the organic phase has been performed thanks to stripping steps involving ammonium oxalate, ammonium carbonate, and sodium carbonate as stripping agents.
ABSTRACT
The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complexes, bearing a hydrotris(1-pyrazolyl)borate (Tp) ligand, have been investigated. These complexes are promising candidates for observation of parity violation (symmetry breaking due to the weak nuclear force). New chiral oxorhenium complexes have been synthesized, namely, [TpReO(eta2-O(CH3)CH2CH2O-O,O)] (4a and 4b) diastereomers and [TpReO(eta2-N(CH3)CH2CH2O-N,O)] (5) and [TpReO(eta2-N(tBu)CH2CH2O-N,O)] (6) enantiomers. All compounds could be obtained in enantiomerically pure form by using either column chromatography or HPLC over chiral columns. VCD spectroscopy of these compounds and of [TpReO(eta2-N(CH3)CH(CH3)CH(Ph)O-N,O)] (2) and [TpReO(eta2-N(CH2)3CHCO2-N,O)] (3) (with chiral bidentate ligands derived, respectively, from ephedrine and proline) were studied. This allowed the absolute configuration determination of all compounds together with their conformational analysis, by comparing calculated and experimental spectra. This is the first VCD study of rhenium complexes which further demonstrates the applicability of VCD spectroscopy in determining the chirality of inorganic complexes.
