Aminodifluorophosphine: crystal and molecular structure at 95 K, and vibrational spectra of condensed phases

Abstract

The crystal and molecular structure of PF₂(NH₂) has been determined at 95 K. A single crystal was grown in situ on a Weissenberg goniometer and transferred to a CAD4 diffractometer for data collection. Crystals of PF₂(NH₂) are monoclinic, space group P2₁/c, with a= 5.2125(26), b= 12.830(5), c= 4.896(4)Å, β= 115.07(6)°, and Z= 4. Two quadrants of data were collected and merged to give 1 300 reflections, of which 1 243 were considered to be above background. The final R was 0.0376. The P–N bond length is 1.6384(9)Å, while the P–F(1)[1.6083(11)Å] and P–F(2)[1.5899(6)Å] distances are inequivalent and reflect the involvement of F(1) in intermolecular hydrogen bonding. The N is also hydrogen bonded and the intermolecular bonding gives rise to a corrugated layer of PF₂(NH₂) molecules. Infrared and Raman spectra of PF₂(NH₂) in the liquid, unannealed solid, and crystalline phases have also been recorded and analysed. Spectra of the crystalline solid, formed by a spontaneous annealing process at 110 K, are consistent with the crystal structure, showing shifts in N–H stretching frequencies, and at least one band, absent for non-crystalline phases, assigned to deformations of the hydrogen-bonding network. Stretching frequencies for N–H bonds in NHD species have been used to give accurate N–H bond lengths, and the combined X-ray and spectroscopic data allow the hydrogen-bonding contacts within the crystal, which determine the overall crystal packing, to be fully characterised.