Chemistry

Taking the Heat

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Science  18 Apr 2008:
Vol. 320, Issue 5874, pp. 290
DOI: 10.1126/science.320.5874.290c

Ceramics are often prepared by heating structurally well-defined molecular or polymeric precursors to very high temperatures; in the process, peripheral hydrogen and halide (X) atoms are expelled as HX gases, and the severed bonds of the remaining solid rearrange into a rigid network that lends the material stability. When prepared in this manner, the amorphous ceramic SiBNC shows impressive resistance against thermal or oxidative degradation. Somewhat surprising is the key contribution of carbon, which traditionally segregates from nitrogen during pyrolysis. Sehlleier et al. monitored the fate of the carbon precursor (methylamine) during the synthesis of this material, and found strong evidence that in this case, C-N bonds remain intact even at 1400°C. Their study relied on double isotopic labeling (13C and 15N) of the precursor and subsequent analysis of the ceramic by solid-state nuclear magnetic resonance spectroscopy. Application of the rotational echo double-resonance technique revealed the distribution of bonding distances between the two labeled nuclei and suggested some degree of multiple bonding through π overlap. — JSY

Angew. Chem. Int. Ed. 47, 10.1002/anie.200705786 (2008).

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