Cesium cations

The toxicology, occupational health hazards, and transportation regulations of cesium compounds result from the anion rather than the cesium cation. Producers and distributors provide an MSDS as well as detailed shipping requirements for each product. 

The cesium chloride lattice consists of a simple cubic array of chloride anions with a cesium cation at the center of each unit cell. 

Na -loess clay, where batch experiments were analyzed by X-ray diffraction and infrared and far-infrared measurements. The adsorption isotherm (Fig. 8.36) shows that loess clay is selective for cesium cations. The raw material contained a large amount of quartz, and the clay material was a mixture of kaolinite and an interstrati-fied iUite-smectite mineral as a result, equilibrium Cs" adsorption data are not consistent with a single site Langmuir model. Cesium adsorption on this particular soil clay occurs by cation exchange on sites with various cesium affinities. At low concentration, far-infrared spechoscopy shows the presence of very selective adsorption sites that correspond to internal collapsed layers. At high concentration, Cs MAS-NMR shows that cesium essentially is adsorbed to external sites that are not very selective. 

Reactions of ruthenium catalyst precursors in carboxylic acid solvents with various salt promoters have also been described (170-172, 197) (Table XV, Expt. 7). For example, in acetic acid solvent containing acetate salts of quaternary phosphonium or cesium cations, ruthenium catalysts are reported to produce methyl acetate and smaller quantities of ethyl acetate and glycol acetates (170-172). Most of these reactions also include halide ions the ruthenium catalyst precursor is almost invariably RuC13 H20. The carboxylic acid is not a necessary component in these salt-promoted reactions as shown above, nonreactive solvents containing salt promoters also allow production of ethylene glycol with similar or better rates and selectivities. The addition of a rhodium cocatalyst to salt-promoted ruthenium catalyst solutions in carboxylic acid solvents has been reported to increase the selectivity to the ethylene glycol product (198). 

The favored side-chain alkylation over ring alkylation is interpreted by the geometric constraints exerted by the large rubidium and cesium cations within the zeo-lite supercage. These result in steric restriction of the formation of transition states that would lead to ring alkylation products. 

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. 

Zeolite rho was prepared from aluminosilicate hydrogels containing sodium and cesium cations. The procedure is entirely comparable with the synthesis of faujasite except for substitution of CsOH for about 10% of the NaOH in the faujasite synthesis gel. Alumina trihydrate (Alcoa C-33 grade) was dissolved in 50% NaOH solution at 100°. After cooling to ambient temperature, the required amount of CsOH solution was added, and the resulting liquor was blended into 30% silica sol (duPont Ludox LS-30) with vigorous mixing. After 3-7 days incubation at 25°, the synthesis gel was held at constant temperature, 80, 90, or 100°, until crystals formed maximum crystallinity was usually achieved in 2-4 days. 

Gas products from the alkylation of acetonitrile were regularly analysed using the same column as used for the side-chain alkylation of toluene. Liquid products were also collected every 30 minutes in an acetone-ice bath, but were analysed using a Porapak Q column at 150-180 °C with a helium carrier gas flow rate of 30 ml/min. To investigate the effect of carbonated catalysts, especially that with the excess cesium cation "clusters", carbon dioxide was introduced to the fresh CsNaX-CsOH at the reaction temperature, 350 °C, for 30 minutes before the alkylation of acetonitrile was carried out in a flow of helium. The cesium clusters of treated catalysts were presumed to be fully carbonated (CS2CO3) clusters and the activity of this catalyst was compared with the untreated CsNaX-CsOH. 

The formation of the polynucleotide structure poly(I) is strikingly cation dependent, and relates to the size of the alkali metal cation in the central cavity. Lithium and cesium cations are too small or too large respectively to bind effectively. Na+ occupies a site that is 2.2 A away from four carbonyl oxygens, while K+ is able to occupy a site 2.8 A away from eight carbonyl oxygens.101... 

The slightly less negative value found for the entropy term can be explained by the preorganization of the ligand in the 1,3-alternate conformation, where only a small part of the crown ether moiety is rather flexible. This flexibility is lost with the large cesium cation, which fits very well into the cavity created by the polyether ring and the aromatic nuclei.34... 

Electrospray Ionization/Mass Spectrometry (ES/MS), a soft-ionization desorption technique using polar solvents such as water, methanol, or acetonitrile, was used for direct measurement of cations in solution. The first measurements carried out with mono or bis(crown-6) calix[4]arenes from an equimolar cation-extractant solution confirm that the calixarenes mono(crown-6) extract only one cesium cation. On the contrary, in the same conditions, bis(crown-6) calix[4]arenes can extract two cesium cations for a ratio Cs/BC6 equal to 2.5. The binuclear complex (composed of two cesium cations) is the major species. Cesium/sodium selectivity measurements implementing various mono or bis(crown-6) calix[4]arenes were in agreement with liquid/liquid results.42... 

DCE diluent. However, the differences between the stronger fluorinated modifiers and the weaker nonfluorinated modifiers are much more pronounced. This could be due to the fact that the stronger modifiers may be sufficiently acidic to be partly deprotonated when contacted with the alkaline simulant. The alkoxide form of the alcohol would serve as the counteranion to the extracted cesium, eliminating the need for an anion from the aqueous phase (e.g., nitrate) to be coextracted, and, in turn, making it energetically easier to transfer the cesium cation to the solvent phase, hence increasing the cesium distribution ratio. 

Biphasic conditions also circumvent the salt solubility problem but classic phase transfer conditions using aqueous sodium hydroxide suffer from competing hydrolysis of the phosphorus(III) esters. However, Kem and co-workers found that butyl esters (their substrate was dibutyl phosphonate) are sufficiently stable to provide Michaelis-Becker products in high yields dialkylphosphine oxides were also suitable substrates.67 Salvatore and co-workers have recently developed an efficient biphasic solid-liquid procedure utilising the cesium cation effect Protocol 7. 

The particular influence of cesium ions on the course of cyclization reactions which is proven by many comparison experiments with different metal cations has been called the cesium effect . As a rule, equimolar amounts of cesium compounds are used, which means that one cannot normally speak of a cesium catalysis. Nevertheless, a catalytic effect with respect to the cesium cation often cannot be excluded. 

Buter and Kellogg proceeded on the assumption that cesium salts of carboxylic acids due to their big ionic radii and the high polarizability of the cesium cation are present in DMF as weakly solvatized tight ion pairs [51]. This assumption was based on measurements, which showed that cesium salts with soft anions as e.g. delocalized carbanions in THF exist as contact ion pairs... 

Vogtle and Meurer explained the favoured formation of strain ring compounds in the synthesis of cyclophanes by cyclizations with cesium thiolates by a preorientation (preorganization) of the reactants at the cesium cation [82], For the cesium ion in contrast to the smaller alkali metal cations the capabiUty of forming an 11-membered intermediate is ascribed, which would favour an intramolecular course of the reaction (Fig. 4). 

In the lithium and cesium enolates of o-methoxyacetophenone, the methoxy oxygen coordinates with the smaller lithium cation but not with the cesium cation . Other examples of lithium enolate chemistry include a thermochemical analysis of the aldol reaction of lithiopinacolonate with pivalaldehyde and a comparison of the proton affinities and aggregation states of lithium alkoxides, phenolates, enolates, -dicarbonyl enolates, carboxylates and amidates. Although the lithium enolate of cyclopropanone itself remains unknown, derivatives (accompanied by their aUenoxide isomer) have been implicated in the reaction of a-(trimethylsilyl) vinyl lithium with CO. That both species are seemingly formed is surprising because cyclopropanone enolate is expected to be much less stable than its acyclic isomer cyclopropene is less stable than allene by almost 90 kJmol-. ... 

The synthesis of borosilicalite-1 in fluoride containing media can lead to B/u.c. higher than 4, the maximum amount obtained in alkaline media. The sine qua non condition is to use potassium or cesium cations instead of the usual sodium ions. DB-NMR data, the xmit cell volume and FTIR data confirm the high amount of boron per unit cell and the specific role of K+ and Cs+ ions to stabilize the framework [SiOB] negative charges. 

Analysis of many different salts show that the salts all have ordered packing arrangements, such as those described earlier for NaCl and CaF2. Another example is the salt cesium chloride, where the ratio of cations to anions is 1 1 just as it is in sodium chloride. However, the size of a cesium cation is larger than that of a sodium cation. As a result, the structure of the crystal lattice is different. In sodium chloride, a sodium cation is surrounded by six chloride anions. In cesium chloride, a cesium cation is surrounded by eight chloride anions. The bigger cation has more room around it, so more anions can cluster around it. 

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