Cesium suboxides

The drop in the work function for cesium suboxides is explained as being caused by a quantum size effect. 47) The electronic structure of the suboxides is discussed in terms of a simple stractural model with clusters occupied by the 0 ions. The interior of the clusters is highly repulsive for the conduction electrons and the clusters are separated within a Fermi wave length. These model calculations lead to a decrease in work function with respect to Cs by 0.1 and 0.9 eV for CS7O and Csj 103, respectively. 

A sample of a suboxide of cesium gives up 1.6907% of its mass as gaseous oxygen when gently heated, leaving pure cesium behind. Determine the empirical formula of this binary compound. 

A very narrow 0 2p band is observed with earlier measurements (74) on partially oxidized Cs films, and the result has been discussed in terms of isolated ions incorporated into the films under a surface layer of metallic cesium. This interpretation is very near to reality. Unfortunately, these investigations have been performed with 10.2 eV excitation energy. So the core levels of Cs are not recorded but the measurements definitely refer to Cs suboxides. In this respect it is interesting that during the early stages of oxidation of K (75) and Sr (76, 77) very narrow 0 2p bands are observed, although bulk suboxides of these materials are not yet known. 

In order to identify the oxygen-carrying species responsible for the enhanced performance, it was decided to sample the converter gas phase by mass spectrometry. Since cesium can form suboxides with amu around 1,500 (CsjjOj) and because quadrupole mass spectrometers suffer from a transmission loss as the amu rises, a time-of flight mass spectrometer (TOFMS) was chosen. 

Carbon suboxide, 52 Carbonylation, 148, 149, 216 Carbonyl chlorofluoride, 48, 54 Carbonyl cyanide, 60-61 N,N -Carbonyldiimidazole, 61 1,1-Carbonyldi-l,2,4-triazole, 61 N-Carbonylsulfamic acid chloride (N-Carbonylsulfamyl chloride), 61 Carboxamides, 270 Carboxamine-N-sulfochlorides, 70 p-Carboxybenzenediazonium chloride, 62 p-Carboxybenzenesulfonazide, 62 Carboxylation, 15, 16 Carboxylic acid anhydrides, 133 Carboxylic acid N,N-dimethylamines, 153 Carboxylic anhydrides, 409-410 p-Carboxyphenylhydrazones, 62 Cardenolides, 130, 131 (S-Carotene, 19 /-Carvone, 451, 452 i//-Caryophyllene, 149, 150 Catechol, 65, 233 Catechol amines, 159 Catechyl phosphorus tribromide, 63 Catechyl phosphorus trichloride, 63 Cis-Cecropia juvenile hormone, 261 Cedrene, 234, 235 a-Cedrene, 349 /3-Cedrene, 349 Cendranoxide, 234, 235 Cephalosporin C, 48 Ceric ammonium nitrate, 63-65 Ceric sulfate. 65 Cesium fluoride, 346 trans-Chalcone oxide, 422 Chalcone phenylhydrazones, 257, 258 Chalcones, 406 Chloramine, 65-66, 69 Chloranil, 66-67, 113, 116, 401,454... 

The presence of any electron donor able to stabilize the cation will therefore favor cluster disruption. Such limiting conditions make it very difficult to find an adequate medium for the stabilization of such kinds of clusters. Solvent as well as counterions must be highly inert indeed, both as oxidation agent and as a Lewis base. Although the severity of such limiting conditions increases with increasing atomic weight of the metals, it has been possible to achieve the conditions under which clusters of the elements rubidium and cesium can exist, namely as the suboxide to be described in this Section. 

The formation of homonuclear bonding between alkali-metal atoms which characterizes the formation of cluster species implies that these elements are in an intermediate oxidation state between 0 and 4- 1. This condition appears to be met by the suboxides of rubidium and cesium. 

Selected characteristics of the suboxides of rubidium and cesium are summarized in Table 4.4. 

In the metal-rich suboxides the metal is concentrated in purely metallic regions. In Fig. 4.8, a scheme of the structure of the phase Rb60 is reproduced. There the Rb902 clusters are arranged in layers that alternate with others of metallic rubidium atoms. In the case of the CS7O as illustrated in Fig. 4.9 the CS11O3 clusters are arranged to form columns which are in turn surrounded by purely metallic cesium atoms. 

In contrast to transition-metal molecular clusters, the alkali-metal suboxides are stable only in the solid state. As described in Table 4.4, these clusters decompose at temperatures rather below the melting point of the metals. The stability of these species appears to be relatively precarious. It is very probable that the stabilization of this class of extreme electron-deficient compounds is possible only at relatively low temperature and in strong reducting media such as the alkali-metals rubidium or cesium. 

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. 

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