Cesium complexes crown ethers

Cerium tetrakis(acetylacetonate), 1114 Cesium complexes crown ethers, 40 Chevrel phases, 1321 Chlorella vulgaris nitrate reductase structure, 1438 Chlorine cations... 

With the larger racemic cr-hydroxy-l-naphthaleneacetic acid too, extraction takes place in the presence of 1309] and the appropriate cations but enantiomeric differentiation is not observed. These results were confirmed in transport experiments in which the alkali mandelate is carried through a liquid membrane of [309] dissolved in chloroform. Lehn et al. (1978) explain these observations in terms of an ion pair included in the cavity of the crown ether. The reversal of chiral recognitions between potassium and cesium mandelate of 25% indicates that the structures of the two complexes are different. 

All alkali and ammonium DNM salts have been prepared and characterized. Solid state structures of the potassium, cesium, tetramethylammonium and a potassium crown-ether complex of DNM are available . 

The structure of [Cs(l8-crown-6)z]+e has been determined 109 Because the efectride anions are extremely poor scatterers compared to the large cesium cation (and to a lesser extent the C and O atoms of the crown ether), the structure has the odd appearance of complexed metal cations with no corresponding anions (Fig. 12.50b). However, the most likely position of the electrons can be inferred from the presence of cavities of 240-pm radius presumably the electrons are located in these cavities. 

Thuery, P., Nierlich, M., Bryan, J.C. et al. 1997. Crown ether conformations in 1,3-calix[4]arene bis(crown ether) Crystal structures of a cesium complex and solvent adducts and molecular dynamics simulations. J. Chem. Soc. Dalton Trans. 1997 (22) 4191 4202. 

In the second project, gathering nine teams from six EC countries, more than 150 new extractants were prepared and studied, and the target was reached for the decategorization of waste. Dialkoxy calix[4]arene-crown-6 for cesium, octaamide calix[8] arenes, and CMPO-like calixarenes for actinides display much higher complexing and extracting abilities than other classical extractants, crown ethers, or dicarbollides proposed and sometimes used for this purpose. 

MD simulations performed on calix[4]arene-monocrown-6 and on calix[4]arene-bis-crown-6 and their alkali complexes, suggested that incorporation of aromatic groups in the crown ether loop was a possible way to enhance cation binding and cesium over sodium selectivity.45... 

Extraction of tetrahedral pertechnetate anion from aqueous solutions using several crown ethers is well known. The coextraction of cesium (or strontium) and technetium from nuclear waste by calix[4]arene-crown-6 has been reported from alkaline media. Although technetium in its common pertechnetate form does not complex directly with crown ethers, pertechnetate extraction may be facilitated by crown ethers as the coanion of sodium (for alkaline nitrate waste). Pertechnetate at trace levels in the waste may be more than a 1000-fold more extractable than the smaller nitrate anion in ion-pair extraction processes.87... 

In the early 1990s, there existed several classes of extractants for actinides (CMPO), for cesium and more generally alkali cations, and for strontium and alkaline earth cations (crown ethers and cosan). The combination of these extractants and the grafting of these functions on calixarene platforms have led to new classes of extremely efficient and selective extractants, in particular calixarene-crown, which are presently applied in the United States to treat the huge amounts of waste at the SRS. Calixarenes/ CMPO, crown ethers/cosan, CMPO/cosan, and more recently calixarenes/CMPO/ cosan are promising compounds. It is desirable that these studies, conducted at the international level, continue in particular to obtain a better understanding of the complex mechanisms of extraction of these compounds.127187... 

The podand 52a as well as the macrocycle 54 show the ability to complex sodium ions with their methoxy functions. The macrocycle exceeds the open-chained compound with regard to the complexation constant by a factor of six. While 52a complexes only Na , 54 shows increasing complex constants for K and Cs with a distinct selKtivity for the larger cesium ion. The order of magnitude of the constants of the alkali-metal complexes corr ponds to those of the crown ethers [51]. 

They served for studies of the influence of the cation complexation on the absorption spectra of the coloured compounds ( chromoionophotes )- The cycli-zation of the crown ether ring started from the cesium salt of the 1,3-azulene dicarboxylic acid 52 and the ditosylate 53 a and 53b and led, under dilution conditions [1] with DMF as solvent, to the lactones 54a and 54b with yields of 66 and 43 % respectively. 

The investigation of thia crown ethers, e.g. trithiacyclononane (64, 9S3 ). wh< complexation properties towards transition metal cations were of interest [61,62], was complicated for a long time by the low yields obtained from the corresponding cyclization reactions [63]. The combined application of the cesium effect and of the high dilution principle [1] in the reaction of 1,2-dichloroethane and the dithiol 63 led to an increase of the yield of 64 from 4.1 % (tetraalkylammonimn methano-late as the base) [64] to 50% [65, 66]. 

In contrast to conventional cation exchangers, a reversed elution order is observed with crown ether phases, which is mainly determined by the size ratio between crown ether ring and alkali metal ion. Due to the high affinity of poly(benzo-15-crown-5) toward potassium and rubidium ions, these are more strongly retained than lithium, sodium, and cesium ions, respectively. However, the complexing properties of crown ethers also depend on the counter ion being employed. Thus, in potassium salts, for example, an increase in retention in the order KC1 < KBr < KI is observed with an increasing size of the counter ion. 

Radiocesium is a significant issue as a part of the DOE clean-up effort Selective sequestration of cesium has been addressed by polymer-bound crown ethers e.g. the SuperLig 644) and the crystalline silicotitanates. While both of these methods are effective, they each have their drawbacks. By lining the pores of SAMMS with ferrocyanide complexes, it is possible to remove all the cesium from waste simulant solutions in a matter of minutes [12]. This sorbent is not... 

The relative stability constants of the crown ether complexes (18C6) with sodium, potassium, rubidium, and cesium in glycerol solution were measured... 

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