Spectroscopic properties of uranyl crown ether complexes in non-aqueous solvents

Abstract

The spectroscopic properties of the complexes of uranyl with oxacrowns, azacrowns, thiacrowns of different ring size, polyethyleneglycols , and [2.2.1] and [2.2.2] cryptands were studied in acetonitrile and propylene carbonate solutions by absorption and luminescence spectroscopy. Depending on the ligand, marked differences in the fine structure of the spectra were observed. The crown ethers with six oxygen atoms (18-crown-6, dicyclohexano-18-crown-6, benzo-18-crown-6, dibenzo-18-crown-6 and [2,4]-dibenzo-18crown-6) form inclusion complexes with the uranyl ion in the central cavity. In the case of 18-crown-6 and dibenzo-18-crown-6, a complex with a high coordination symmetry is formed. Outer-sphere complexes are formed with the crown ethers with small ring size (12-crown-4 and 15-crown-5) and with PEG-200. Only minor changes in the spectra were observed when changing the ligand. The spectra of the large crown ethers ([3,4]-dibenzo-21crown-7, dibenzo-24-crown-8 and dibenzo-30-crown-10), together with those of PEG-300 and PEG-400 show that these ligands coordinate in the equatorial plane to the uranyl ion. In the presence of competing inorganic ligands like chloride and nitrate ions, the crown ether is replaced in the first coordination sphere. Azacrowns and cryptands coordinate externally to the uranyl ion, and the corresponding spectra do not show fine structure. In the case of the thiacrowns, no coordination of the ligand to the uranyl ion was observed.

Molecular Dynamics Study on the Adsorption of UO22+ from an Aqueous Phase: Effect of Grafting Dibenzo Crown Ether and Dicyclohexano Crown Ether on the Polystyrene Surface

“…The free-energy analysis suggests that the binding of UO 2 2+ onto dibenzo crown ether (DBCE) and dicyclohexano crown ether (DCHCE) is favorable among the various crown ethers available. 17,18 Thus, DBCE and DCHCE would be ideal candidates for the adsorption of UO 2 2+ ions. The UO 2…”

“…Zolotov observed that polymerized crown ether enhances the adsorption of uranyl ions from the seawater using the metal binding reaction. The free-energy analysis suggests that the binding of UO 2 2+ onto dibenzo crown ether (DBCE) and dicyclohexano crown ether (DCHCE) is favorable among the various crown ethers available. , Thus, DBCE and DCHCE would be ideal candidates for the adsorption of UO 2 2+ ions. The UO 2 2+ binding or adsorption on the crown ethers have laid important understanding as these ions show competitive interactions with the solvent molecules and crown ethers .…”

Uranyl complexes formed with a para-t-butylcalix[4]arene bearing phosphinoyl pendant arms on the lower rim. Solid and solution studies

“…Physicochemical properties of simple uranyl compounds have been widely studied in aqueous solution [4,9,10], in organic solvents [6,[10][11][12], and in the solid state [13,14]. Semi-empirical [15,16] and first-principles studies [17] have been essential to decipher the electronic and vibronic states, the nature of the chemical bonds in uranyl coordination compounds [18][19][20], as well as to model extraction mechanisms [21].…”

Factors affecting the suitability of superplasticiser-amended cement for the encapsulation of radioactive waste

“…Changes in the luminescent properties of the uranium indicate that, for the longer PEG chains (PEG-300 and 400), inclusion complexes were formed, whereas for smaller chains, the organic molecule coordinates to the uranyl ion through its second coordination sphere. Despite the extensive use of crown ethers for the separation of lanthanide and actinide mixtures (Servaes et al, 2004), as well as the use of PEG-aqueous biphasic systems for similar purposes (Chen et al, 2005), there are few data describing stability constants for the coordination of UO 2 2+ with either crown ethers or PEG molecules in aqueous media. The only available formation energies or stability constants for U(VI) with crown ethers have been reported in organic solutions (Rounaghi and Heydari, 2008;Rounaghi and Kakhki, 2009).…”

“…They observed an internal hydrogen bond between the oxygen atoms in positions O5 and O11, causing cyclising of the PEG molecule, which adopts a configuration similar to the crown ether complex. More recently, Servaes et al (2004) investigated the spectral properties of uranyl complexes with PEG-200, PEG-300 and PEG-400 in acetonitrile and propylene carbonate solutions. Changes in the luminescent properties of the uranium indicate that, for the longer PEG chains (PEG-300 and 400), inclusion complexes were formed, whereas for smaller chains, the organic molecule coordinates to the uranyl ion through its second coordination sphere.…”