Suboxides group

Materials for PC Media. Crystalline alloys of elements from the fifth and sixth main group are preferred (3,103,109—111). As the first PC materials, tellurium suboxides as well as Te/Se or Te films that had been doped with small amounts of other elements like Ge, As, or Sb to shift the crystallization point to >100°C have been described. 

Reactions. Heating an aqueous solution of malonic acid above 70°C results in its decomposition to acetic acid and carbon dioxide. Malonic acid is a useful tool for synthesizing a-unsaturated carboxyUc acids because of its abiUty to undergo decarboxylation and condensation with aldehydes or ketones at the methylene group. Cinnamic acids are formed from the reaction of malonic acid and benzaldehyde derivatives (1). If aUphatic aldehydes are used acryhc acids result (2). Similarly this facile decarboxylation combined with the condensation with an activated double bond yields a-substituted acetic acid derivatives. For example, 4-thiazohdine acetic acids (2) are readily prepared from 2,5-dihydro-l,3-thiazoles (3). A further feature of malonic acid is that it does not form an anhydride when heated with phosphorous pentoxide [1314-56-3] but rather carbon suboxide [504-64-3] [0=C=C=0], a toxic gas that reacts with water to reform malonic acid. 

All the refractory metals of Group IV and Group V form volatile suboxides at high temperatures. Just as the stability of carbon monoxide increases with an increase in temperature, these oxides also become more stable at higher temperatures. The vapor pressures of these suboxides can be calculated from the relationship ... 

The decompositions of C302, CO, C02, CS2, COS, CSe2 and COSe are dealt with in this section. Apart from carbon suboxide, this is a group of stable, un-reactive compounds. Considerable emphasis has been placed on the investigation of the photolytic decompositions of some of these compounds which are thought to provide useful sources of atoms (C, O, S and Se) and free radicals (C20). The photochemistry of carbon dioxide has particular relevance to the chemistry of planetary atmospheres, although to date the mechanism of C02 photolysis remains obscure. 

Table 3.1-1 summarizes the crystallographically characterized group 1 metal suboxides, and group 2 metal subnitrides, the latter containing additional alkali or other metals [25]. 

KETENES. Members of a class of compounds which contain the functional group —C—C-O. Examples arc keiene itself (CH CO), methylkeienc CH(CH=C=0. dimelhylkctene (CHi). C=C=0. diphenyi-kcicnc (C(,Hx) C=C=0. and carhon suboxide ()=C=C=C=O. Of these, keiene is by far the most important. It is a reactive, colorless gas of considerable industrial importance Physiologically, it is extremely poisonous and care must be taken to avoid breathing it. 

Discrete [BaeN] clusters are found in the crystal structure of (BaeN)Nai6, as shown in Fig. 12.6.4. (Ba6N)Nai6 crystallizes in space group Im3m with a = 1252.7 pm and Z = 2. The Na atoms are located between the cluster units, in a manner analogous to that in the low-valent alkali metal suboxides. 

A. Simon, Alkali and alkaline earth metal suboxides and subnitrides. In M. Driess and H. Noth (eds.), Molecular Clusters of the Main Group Elements, Wiley-VCH, Weinheim, 2004, pp. 246-66. 

A special case of molecular boron suboxides is found in the hydroxylated polyhedral boranes (see Boron Hydrides). For example, the icosahedral anion closo- Q 2H 2 and related compounds can be completely hydroxylated to form discrete molecular boron suboxides, including closo-[Bi2(OH)i2] These can be regarded as members of a class of formally hydrated suboxides related to compounds snch as tetrahydroxydiborane, B2(HO)4 (BO H2O). The terminal hydroxyl groups of these compounds can be fimctionahzed as esters or ethers to produce a variety of large molecule derivatives. 

After noting some suboxides which are peculiar to Rb and Cs we shall describe the crystal structures of metal oxides in groups in the following order M3O, M2O, MO, MO2, MO3, MO4 M2O3, M2OS, M2O7, M3O4, and miscellaneous oxides M O, . The remainder of the chapter is devoted to brief surveys of the oxides of certain metals which present points of special interest. 

Recently titania appeared as a non-conventional support for noble metal catalysts, since it was found to induce perturbations in their H2 or CO adsorption capacities as well as in their catalytic activities, This phenomenon, discovered by the EXXON group, was denoted "Strong Metal-Support Interactions" (SMSI effect) (1) and later extended to other reducible oxide supports (2). Two symposia were devoted to SMSI, one in Lyon-Ecully (1982) (3) and the present one in Miami (1985) (4) and presently, two main explanations are generally proposed to account for SMSI (i) either the occurence of an electronic effect (2,5-13) or (ii) the migration of suboxide species on the metal particles (14-20). The second hypothesis was essentially illustrated on model catalysts with spectroscopic techniques.lt can be noted that both possibilities do not necessarily exclude each other and can be considered simultaneously (21). 

It should be mentioned that the a //-types of the clusters are well known The complex halide anion M2X9 occurs with many main group and transition metals. The M3X11 cluster occurs (but not as an isolated unit) in Nb3Se4. (23) The characteristic structural units of alkali metal suboxides are shown in Fig. 3. The Rb902 clusters are only found in pure Rb suboxides and highly oxidized samples (see III.2.) the Csxi03 cluster is a constituent of the Cs and Rb-Cs suboxides. 

Carbon suboxide (review [iOO]) and 2-methyIaminopyridine give an excellent yield of an inner salt [2288]. A bis(methylthio)methylene derivative of Meldrum s acid (review of its properties [3949]) is a versatile source of three ring-carbon atoms and an attached carboxyl group in this reaction [4000]. 

It is clear that further work will be required to elucidate the details of the mechanistic pathway for the polymerization of carbon suboxide. Both the mechanism proposed by Ulrich (39) and the above zwitterionic mechanism lead to a functionality of two ketenyl groups per molecule. 

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