Figure Nine

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Science  20 Jul 2012:
Vol. 337, Issue 6092, pp. 271
DOI: 10.1126/science.337.6092.271-b

Nitrogen occurs naturally as a rather tightly bound neutral dimer, and anionic azide (N3) salts have long been accessible as well. A cation composed purely of nitrogen arrived only much more recently on the scene, with the preparation of an N5+ salt about a decade ago. The heavier congener phosphorus has followed a similar path: a variety of well-established neutral and negatively charged morphologies, but until now no tractable cation salts. Köchner et al. have filled the gap with the preparation of a P9+ salt. Key to its isolation was the use of an especially inert, aluminum-centered counterion adorned with trifluoromethyl groups. The synthesis entailed oxidation of neutral P4 by the nitrosonium salt of this counterion in dichloromethane solvent. Ultraviolet irradiation facilitated reaction of an apparent [P4NO]+ intermediate (and precipitation of excess neutral phosphorus) without damaging the ultimate product, which was isolable as a yellow-orange powder. Nuclear magnetic resonance spectroscopy in conjunction with theoretical calculations revealed a figure 8-type structure, of D2d symmetry, in which a central tetracoordinate P atom bridges two clusters of four P atoms each. The salt was also characterized by mass spectrometry and infrared and Raman spectroscopy, and persisted for weeks in room-temperature solution. The authors envision prospective applications of the salt in currentless deposition protocols.

Angew. Chem. Int. Ed. 51, 6529 (2012).

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