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Structure and Conformation of the Medium-Sized Chlorophosphazene Rings

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journal contribution
posted on 02.09.2014, 00:00 by David J. Bowers, Brian D. Wright, Vincenzo Scionti, Anthony Schultz, Matthew J. Panzner, Eric B. Twum, Lin-Lin Li, Bryan C. Katzenmeyer, Benjamin S. Thome, Peter L. Rinaldi, Chrys Wesdemiotis, Wiley J. Youngs, Claire A. Tessier
Medium-sized cyclic oligomeric phosphazenes [PCl2N]m (where m = 5–9) that were prepared from the reaction of PCl5 and NH4Cl in refluxing chlorobenzene have been isolated by a combination of sublimation/extraction and column chromatography from the predominant products [PCl2N]3 and [PCl2N]4. The medium-sized rings [PCl2N]m have been characterized by electrospray ionization–mass spectroscopy (ESI-MS), their 31P chemical shifts have been reassigned, and their T1 relaxation times have been obtained. Crystallographic data has been recollected for [PCl2N]5, and the crystal structures of [PCl2N]6, and [PCl2N]8 are reported. Halogen-bonding interactions were observed in all the crystal structures of cyclic [PCl2N]m (m = 3–5, 6, 8). The crystal structures of [P­(OPh)2N]7 and [P­(OPh)2N]8, which are derivatives of the respective [PCl2N]m, are also reported. Comparisons of the intermolecular forces and torsion angles of [PCl2N]8 and [P­(OPh)2N]8 with those of three other octameric rings are described. The comparisons show that chlorophosphazenes should not be considered prototypical, in terms of solid-state structure, because of the strong influence of halogen bonding.