Abstract
POLYSILANES are used as resists in microlithography and as precursors for silicon carbide ceramics1–3. We have been investigating the formation of polysilanes by the reductive dechlorination polymerization of dichloro-organosilanes with sodium4—a modification of the well-known Wurtz reaction, in which organic halides are reductively coupled using sodium to form carbon-carbon single bonds. In all such reactions, after a period of time a blue precipitate is formed, but no characterization of this solid has so far been reported. It has been suggested (without spectroscopic evidence) that the colour in the polysilane synthesis is due to defects in sodium chloride1, sodium colour centres in sodium chloride3,5, reactive polysilane chain-ends3 or a stabilized organic radical6. The first of these suggestions has been tacitly accepted despite the fact that the most common defects in sodium chloride are F centres (anion vacancies with trapped electrons from excess sodium atoms) which give the salt a yellow colour7,8. Here we present spectroscopic results suggesting that the blue colour is due to colloidal alkali-metal particles formed during the reaction. These particles are contained in a matrix composed of an intimate mixture of polymer and alkali-metal halide, and are remarkably stable in air. It is most unusual for colloidal metal particles to be formed under such mild conditions.
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Benfield, R., Cragg, R., Jones, R. et al. Air-stable alkali-metal colloids and the blue colour in Wurtz syntheses. Nature 353, 340–341 (1991). https://doi.org/10.1038/353340a0
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DOI: https://doi.org/10.1038/353340a0
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