Atomization suboxides

Self-Test 3.9A Describe the structure of the carbon suboxide molecule, C302, in terms of hybrid orbitals, bond angles, and tr- and -ir-bonds. The atoms lie in the order OCCCO. 

Even the extremely electron-deficient alkali metals can form clusters when interstitial atoms contribute to their stabilization. Compounds of this kind are the alkali metal suboxides such as Rb902 it has two octahedra sharing a common face, and each is occupied by one O atom (Fig. 13.16). Flowever, the electron deficiency is so severe that metallic bonding is needed between the clusters. In a way, these compounds are metals, but not with single metal ions as in the pure metal Rb+e-, but with a constitution [Rb902]5+(e )5, essentially with ionic bonding in the cluster. 

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. 

This interesting derivative of ketene is also obtained from benzilic acid by the old process of Staudinger the add is converted, by the action of phosphorus pentachloride, into diphenylchloracetyl chloride from which the two chlorine atoms are removed by means of zinc. (Formulate this equation.) What is carbon suboxide For information about the ketenes see H. Staudinger, Die Ketene, Stuttgart, 1912. 

Fig. 3.1-3. Crystal structures of the binary alkali metal suboxides (a) [Rb902], (b) [Csnn03], (c) [Rb902]Rb3(Rb60), (d) [Csn03]Csio(Cs70), and (e) [Csn03]Cs(Cs40). O atoms drawn as small spheres, for clarity only M-M contacts in the clusters outlined.

Jin, S.H., et ah, Conformal coating of titanium suboxide on carbon nanotube networks by atomic layer deposition for inverted organic photovoltaic cells. Carbon, 2012. 50(12) p. 4483-4488. 

The mesoporous forms of germanium that derive from the above chemistry are very air sensitive and rapidly convert to germanium suboxides GeOx upon exposure in air for a short time (<1 min). This is expected since almost all Ge atoms of the framework lie at or near the surface and the Ge-Ge bond is susceptible in oxidation. The formation of GeOx involves the conversion of Ge-Ge bonds to Ge-O-Ge moieties and seems to be a homogeneous process. This causes a systematic blue-shift of the energy band gap, possibly due to the size-confinement effect. 

Carbon Suboxide Photoiysis. In principle, carbon suboxide (1) can be used as a precursor to atomic carbon and two molecules of carbon monoxide as shown in Eq. 2. However, this reaction is endothermic by 141 kcal/mol and can only be realized in the vacuum ultraviolet (UV) at wavelengths that destroy most organic substrates. However, photolysis of 1 at 1470 A produces C atoms in a low-temperature matrix. The short wavelength flash photolysis of 1 coupled with atomic absorption has been used to measure the rate constants for various spin states of carbon with simple substrates. 

Carbonylcarbene reacts with oxetane in a complex manner, giving cyclopropane and propene by a deoxygenation process and ketene plus ethylene as apparent insertion-fragmentation products (equation 66). The reaction is carried out by irradiation of a solution of carbon suboxide in oxetane under these conditions, photodecomposition of intermediates is possible. The initial attack is believed to be at the ring oxygen atom to give a zwitterionic species (78JA6425). 

The photolysis of carbon suboxide in the near ultraviolet has been studio I by many workers. The formation of C( 3/J) atoms is not energetically possibl< above the incident wavelength, 2066 A. Hence, the primary process must I ... 

The C( S) state lies 2.683 eV above the ground state C(3P) with a lifetime of 2 sec (32). The production of C.( S) atoms is observed in the photolysis of carbon suboxide in the vacuum ultraviolet. The C( S) atom production can be detected by absorption at 2479 or 1752 A. Rate constants of C(1S) with molecules have been measured by Meaburn and Perner (687), Husain and Kirsch (505), and Braun et al (141). The rate constants are in general much smaller (collision efficiencies 10 2 to 10 6) than those for C( D), in analogy with the results for O( D) and O( S) atom quenching rates given in Table IV-3. 

The ground state C atoms are produced by the photolysis of carbon suboxide. They can be monitored by optical absorption at 1657 A. Reactions of C(3P) atoms with molecules have been studied by Husain and Kirsch (497,498) and Braun et al. (141). 

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. 

The reader should note the similarity between the icosahedral fragment in BioHh and the icosahedron that is present not only in crystalline elemental boron, but also in a number of boron compounds such as boron carbide (which may be represented as B12C3), boron suboxide (B12BO2), and the salt K2B12H12. Moreover, similar icosahedra of aluminum atoms... 

No compounds C2O2 or C4O2 have been described it has been suggested that whereas suboxides with an odd number of carbons may be stabilized by forms such as III, such structures may not be drawn for suboxides with even numbers of carbon atoms (Exercise 2). 

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