Cesium cluster

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. 

Of course, more complex systems also exist (see Figure 9.6). Although there is no evidence for the existence of mixed metal clusters as yet, ESR signals show that there might be interactions between sodium and cesium clusters in zeolites. 

Controlled oxidation of mixtures of both rubidium and cesium metals leads under equilibrium conditions only to the cesium clusters CsnOa in the form of the compounds [CsnOaJCsio-xRbx, [CsnOajRbv-xCSx, or [CsiiOajCsi-xRbx. Only after the consumption of all the cesium can the rubidium partially replace the cesium in the clusters. This feature indicates the presence of equilibria between actual chemical species with different relative thermodynamic stabilities. The ionization energy of cesium is lower than that of rubidium. This feature appears to be determinant in the relative stability of the suboxides, higher for CsuOa than for Rb902, deduced from the experiments discussed above. 

These along with fnrther discnssions on recombination processes common to most of these models are covered in Section 3.3.4.1. Recombination is of interest as this is believed to be responsible for many of the signals often used in SIMS, whether in the analysis of elemental or molecular distributions. As an example of the former, recombination is believed to be the primary mechanism responsible in the formation of Cesium cluster ions used in the analysis of elemental distributions (that in which Cesium combines with some element of interest to provide signals displaying reduced matrix effects). As for the latter, recombination appears to be dominant in the formation of protonated molecular ion emissions, as well as those associated with alkali metal elements, and certain transition metal elements. Note These typically display significantly greater intensities than their molecular parent ions. 

In the case of elemental distributions, semi-quantitative imaging can be aided through the collection of Cesium cluster ions (MCs and MCs2, where M is an isotope of the element of interest). This approach, however, requires the use of a Cs primary ion beam and yields poor sensitivity and detection limits relative to their atomic secondary ion emissions. When using this approach, the Cs and/or Cs2 signals should also be collected as these are needed in normalizing the respective... 

Use of the Cesium cluster ion method (analysis of MCs and/or MCS2 secondary ions in which M represents the element of interest with MCs used for the electropositive elements and MCsj used for electronegative elements) can prove useful in understanding the distribution of major or minor elements in unknown matrices. This stems from the significantly reduced matrix effects suffered by these populations. Downsides to this method includes the fact that a Cs primary ion beam must be used, and both the MCs and the MCS2 populations provide poorer sensitivity and detection limits to the elements of interest than their elemental secondary ion counterparts. 

Base catalysis is another area which has received a recent stimulus from developments in materials science and microporous solids in particular. The Merk company, for example, has developed a basic catalyst by supporting clusters of cesium oxide in a zeolite matrix [13]. This catalyst system has been developed to manufacture 4-methylthiazole from acetone and methylamine. 

Figure 9.3 Cluster of unit cells of the cesium chloride crystal structure. This figure shows that ions of the same sign in this structure line up along the 100 directions. Thus the three rows are orthogonal to one another. Translation of a (100) plane of ions over its nearest (100) neighboring plane keeps ions of opposite sign adjacent to one another. This is also the case on the (110) planes, but the translation vector is V2 larger than for the the (100) planes.

The doso-clusters B Hn2-, B10H102-, and B6H62 are stable entities. Their alkali salts are very water soluble. Cesium as a counter-ion reduces the water solubility considerably, and ammonium ions (especially quaternary ammonium ions) precipitate the cluster anions quantitatively from aqueous solutions. The resulting tri- and tetraalkylammonium salts are usually soluble in organic solvents. This allows chemistry to be performed under conditions which are standard for organic... 

Example Cesium iodide is frequently used for mass calibration in fast atom bombardment (FAB) mass spectrometry (Chap. 9) because it yields cluster ions of the general formula [Cs(CsI)n] in positive-ion and [I(CsI)J in negative-ion mode. For the [Cs(CsI)io] cluster ion, m/z 2730.9 is calculated instead of the correct value m/z 2731.00405 by using only one decimal place instead of the exact values Mi33Cs = 132.905447 and M1271 = 126.904468. T e error of 0.104 u is acceptable for LR work, but definitely not acceptable if accurate mass measurements have to be performed. 

Katakuse, 1. Nakabushi, H. Ichihara, T. Sakurai, T. Matsuo, T. Matsuda, H. Metastable Decay of Cesium Iodide Cluster Ions. Int. J. Mass Spectrom. Ion Proc. 1984, 62, 17-23. 

Carboxylate promoters may also be able to coordinate to an Rh(CO)2 fragment, and therefore facilitate a process such as that shown in (45). Reactions of [Rh15(CO)27]3 with H2 in the presence of cesium carboxylates are reported (123) to be consistent with the formation of small equilibrium amounts of Rh(C0)2(02CR) by reaction (45). Carboxylates could therefore be involved in cluster growth or transformation during catalysis. 

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