Silicon skeleton crystals

It is known that during the immersion of PS into the CUSO4 + HF bath, oxidation-reduction reactions between copper ions and silicon atoms from the silicon skeleton of the PS layer can occur [2,4]. This is conditioned by the high redox potential of Cu ions. Copper ions are reduced and Cu deposited via the electron exchange with silicon which is oxidized and dissolved in the fluoride-containing solution. The most important observation from this study for PS of 55% porosity is the crystalline structure of the deposited Cu grains very well faceted Cu crystals are formed at the PS surface and small Cu crystals are within the pore channels. 

The morphological pattern of the products of silicon vapor combustion in gaseous nitrogen at condensation synthesis with skeleton crystal formation as well as denchite growth of silicon nitride crystals in melted metal salts proves the existence of the nonequilibrium mechanism of structure formation in the case of SHS. The mechanism appears to be the basis of the conception of nanodispersed particle formation under the combustion mode [28]. 

Design, synthesis and structure determination of molecules, the skeletons of which are distorted by steric congestion and/or by charge perturbation, therefore, has become an additional research project of the Frankfurt group since 1989 [2,3]. Of the altogether about 100 single crystal structures determined in the meantime, about a dozen are of silicon organic compounds [5] (cf. examples in Fig. 1). 

But, just as among the compounds of carbon, one can find among the minerals instances in which the skeleton is tightly cross-linked. Compare, for example, the crystal structure of diamond with that of cristobalite, one of the many structures adopted by silicon dioxide, whose more usual structure is quartz. As Fig. 9.10 shows, the silicon atoms occupy sites that form a diamondlike structure opened out by the bridging oxygen atoms. 

In continuation of our systematic studies on zwitterionic pentacoordinate silicon compounds, we have now succeeded in synthesizing the molecular A, 5/-silicates 5-10 (for reviews dealing with pentacoordinate silicon compounds, see [13-19]). These zwitterions belong to a new class of spirocyclic pentacoordinate silicon compounds with an SiO C skeleton. They contain diolato(2-) ligands derived from acetohydroximic acid and benzohydroximic acid, respectively (tautomers of acetohydroxamic acid and benzohydroxamic acid). Preliminary data concerning 5 have already been published elsewhere [8]. We report here on the syntheses and properties of compounds 5-10. In addition, the crystal structures of 6 and 8 are described. 

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