Europium cations

The emission spectra were obtained at 298 K and 77 K in the 570—720 nm range. Transitions from the to the Fj (J=0, 1,2, 3, and 4) were observed, which are consistent with a low symmetry around the europium cation which could be occupying a Cnv, Cj, or Q symmetry site. The substitution of two water molecules by a phen molecule (by comparing the complexes [Eu(eta)2 (1120)4] Cl and [Eu(eta)2 (phen) (H20)2]C1) intensify the Dq—> p2 transition. This indicates that the chemical environmental has been changed, since such a transition is a hypersensitive one. The spectra exhibit a number of states higher than 2J+1, su esting that the compounds consist of a mixture of isomers. 

The above hypothesis regarding the effect of deposition of silica on the ability of phen to act as a chromophor is also reinforced by the fact that, for the eta—phen complex, a lowering of the H4 value is observed when comparing the free and silica-based complexes, whereas for eta complex such lowering is not observed, since H4 is related with orientation of the ligand molecule around the europium cation. 

Eug(W07)3.5H20. The presence of five water molecules in the tungstate structure, that is, an extra molecule in relation to the molybdate, can be pointed out as the main factor leading to such quenching phenomena. Furthermore, the presence of a larger number of oxygen atoms in the molybdate structure can promote efficient energy absorption and transfer to the europium cation. 

Normal-type spectra are shown by metals of the d- or f-block where the metal d- or f-electrons are of such low energy that they do not interact significantly with the porphyrin ir-electrons for example, the vanadyl cation, (d ) and the europium cation, Eu(III) (f ). 

Hamacek J, Poggiali D, Zebret S, El Aroussi B, Schneider MW, Mastaleiz M (2012) Birilding large supramolecular nanocapsules with europium cations. Chem Commun 48(9) 1281-1283... 

Although rare-earth ions are mosdy trivalent, lanthanides can exist in the divalent or tetravalent state when the electronic configuration is close to the stable empty, half-fUed, or completely fiUed sheUs. Thus samarium, europium, thuUum, and ytterbium can exist as divalent cations in certain environments. On the other hand, tetravalent cerium, praseodymium, and terbium are found, even as oxides where trivalent and tetravalent states often coexist. The stabili2ation of the different valence states for particular rare earths is sometimes used for separation from the other trivalent lanthanides. The chemicals properties of the di- and tetravalent ions are significantly different. 

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

Solutions of alkali metals in ammonia have been the best studied, but other metals and other solvents give similar results. The alkaline earth metals except- beryllium form similar solutions readily, but upon evaporation a solid ammoniste. M(NHJ)jr, is formed. Lanthanide elements with stable +2 oxidation states (europium, ytterbium) also form solutions. Cathodic reduction of solutions of aluminum iodide, beryllium chloride, and teUraalkybmmonium halides yields blue solutions, presumably containing AP+, 3e Be2, 2e and R4N, e respectively. Other solvents such as various amines, ethers, and hexameihytphosphoramide have been investigated and show some propensity to form this type of solution. Although none does so as readily as ammonia, stabilization of the cation by complexation results in typical blue solutions... 

In aqueous solutions, trivalent lanthanides are very stable whereas only a limited number of lanthanides exhibit a stable divalent or tetravalent state. Practically, only Ce4+and Eu2+ exist in aqueous solutions. The properties of these cations are very different from the properties of the trivalent lanthanides. For example, Ce4+ is more acidic and cerium(IV) hydroxide precipitates at pH 1. Eu2+ is less acidic and europium(II) hydroxide does not precipitate at pH 7—8.5, whereas trivalent lanthanide hydroxides do. Some industrial separations are based on these phenomena. 

This compound constitutes an example of a cation substitution and can be obtained by adding 1.0 g. (0.0029 mole) of europium(III) oxide to the original mixture. It is particularly interesting that under the conditions of the reaction europium(II) is formed. Excitation with a regular ultraviolet lamp of either 2537 or 3660 A. shows intense blue fluorescence. 

As expected, tetravalent thorium is better extracted than trivalent europium. All calixarenes are stronger extractants than TOPO or OOCMPO. The dealkylated series is better than the alkylated one. For the dealkylated series and alkylated series, the sequence of increasing efficiency toward two cations is tetramer < octamer < hexamer. 

The analysis of the extraction by CPo21 data reveals a 1 1 metal ion-to-ligand ratio for europium and thorium. The selectivity factors indicate a good selectivity toward these two cations with respect to Mn2+, Pb2, Cd2+, Fe2+, Ni2+, and Co2+, among which only cadmium is a weakly radioactive fission product.155 A synergistic extraction of almost three orders of magnitude was evidenced for the extraction of La3+, Nd3+, Eu3+, Ho3+, Lu3+ with 4-benzoyl-3-methyl-l-phenyl-5-pyrazolone and CPo21 however, it does not improve the separation factors between lanthanides.156... 

To increase the distribution ratios, a solution of lithium nitrate 1M was used. This salt, which has a common anion with europium and americium to be extracted but a cation which is usually negligibly extracted by other calixarenes, should increase the distribution ratios according to the relation Du = A (JU "[N03- ". It seems that these calixarenes, as several nitrogen ligands do, present a certain affinity for this lithium cation. The lipophilic dicarbollide anion (BrCosan), which is known to facilitate cation extraction, was implemented and led to a strong increase of the extraction of cations from 10 3 M HN03 solutions. Under these conditions, only thiopicolinamide was not able to significantly extract trivalent actinides.187... 

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