Trapping Molecules in a Bowl

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Science  03 Mar 2000:
Vol. 287, Issue 5458, pp. 1557
DOI: 10.1126/science.287.5458.1557b

Even relatively simple molecules can be surprisingly difficult to pin down. Although neutral nitric oxide (NO) and its cation (NO+) are well known, the nitroxyl anion (NO) has been difficult to isolate even as a simple salt (the species known “formally” in some compounds as “bent metal nitrosyls” are still the neutral species). Kawanami et al., in the course of preparing molecular oxides, isolated a vanadium oxide species (V12O32) that stabilizes the NO anion. Previous work had established that the species V12O32 forms a bowl-shaped species bearing four negative charges. The species now isolated has five (CH3CH2)N+ cations, and as there is no evidence for reduction of the oxide bowl, the authors conclude that the extra cation balances a negative charge on the NO species. Indeed, a crystallographic study reveals a slightly longer NO bond length, (almost 1.20 angstroms, versus 1.15 angstroms for neutral NO). In comparison with an analogous complex in which neutral acetonitrile (CH3CN) is trapped in the bowl, NO penetrates more deeply and appears to be “stuck” to its inner surface. Although closed molecular oxide cages are known to trap anionic species, this example is unusual in that an open oxide surface has trapped an otherwise unstable species. The NO complex is remarkably stable—it survives even after heating up to 90°C under vacuum conditions.—PDS

J. Am. Chem. Soc.122, 1239 (2000).

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