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Keywords:

  • Azides;
  • Vibrational spectroscopy;
  • Electron diffraction;
  • Conformation analysis;
  • Ab initio calculations

Abstract

Azido(difluoro)phosphane, F2PN3, is a colorless gas, which freezes to a glassy solid at ca. –120 °C, and the boiling point obtained by extrapolating the vapor-pressure curve is 8 °C. It has been characterized by IR (gas phase, Ar matrix), Raman (liquid, amorphous, and crystalline solid), and 19F, 31P, 14N, and 15N NMR spectroscopy. The conformational properties of F2PN3 have been studied by vibrational spectroscopy, gas electron diffraction (GED), and quantum chemical calculations. An almost equimolar mixture of two conformers was identified in the gas and neat liquid phases, as well as in Ar matrix, for which the N3 group adopts a syn and anti orientation with respect to the bisector of the FPF angle. The syn conformer was found to be slightly more stable than the anti conformer by 2.4 ± 0.6 kJ mol–1H°) determined by gas–phase temperature-dependent IR spectroscopy, but in the crystalline state at low-temperature only the anti form is observed. The very different conformational properties of F2PN3 relative to that of the previously investigated F2PNCO are discussed, guided by a natural bond orbital (NBO) analysis of electron delocalizations and steric exchange repulsions.