Structure and Conformational Properties of Azido(difluoro)phosphane, F₂PN₃

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–1 (ΔH°) 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.

Conformation and Structure of Dichlorophosphoryl Isocyanate in the Gaseous and Solid Phases

“…According to the quantum‐chemical calculations, two energetically similar conformers of F 2 P(O)NCO (Δ E cal = 4.4 kJ mol –1 , CBS‐QB3) are expected to coexist, but instead, only the lower‐energy conformer with the P=O bond being in syn configuration to the NCO group was ascertained in the solid state by low‐temperature X‐ray crystallography. The preference of a single conformation has also been observed in other phosphorus(III) isocyanates F 2 PNCO and Cl 2 PNCO, but instead, two conformers have been observed for the isoelectronic azides F 2 PN 3 . Very recently, the complex conformational landscape of triallyl phosphate has been explored by combining matrix‐isolation IR spectroscopy and density functional theory (DFT) calculations, and more than 50 conformers have been identified …”

Spectroscopic Properties, Conformation and Structure of Difluorothiophosphoryl Isocyanate in the Gaseous and Solid Phase

“…The analogous phosphorus(III) species F 2 PNCO shows only one stable conformer as well. [13,15] Dichlorophosphoryl isocyanate shows two stable conformers, syn and anti, and the barrier to rotation amounts to 2-3 kJ mol À 1 depending on the method and basis set employed for its calculation. [12] Furthermore, different basis set/method combinations predict different energetically preferred conformers for dichlorophosphanyl isocyanate.…”

“…Quantum-chemical calculations proposed the existence of syn-and anti-conformers for both compounds. [15] Anyhow, the fluorinated phosphorus(III) compound F 2 PNCO was examined solely by gas-phase electron diffraction revealing the exclusive presence of a syn-conformer. And the phosphoryl compound was examined only by X-ray diffraction of single crystals, which reveal a dimer formation comparable to the aggregation motive of Cl 2 P(O)NCO.…”

“…The corresponding fluorinated pair F 2 PNCO [13] and F 2 P(O)NCO [14] have been investigated as well. Quantum‐chemical calculations proposed the existence of syn‐ and anti‐ conformers for both compounds [15] . Anyhow, the fluorinated phosphorus(III) compound F 2 PNCO was examined solely by gas‐phase electron diffraction revealing the exclusive presence of a syn ‐conformer.…”

Anorganische Chemie 2011

“…Im Gegensatz zur vorhergesagten C3‐Symmetrie dieser Verbindungen weicht die Molekülstruktur im Festkörper davon stark ab; Ursache sind intramolekulare Wechselwirkungen 1_86. In der Verbindung F2PN3 existiert ein Gleichgewicht zwischen der syn ‐ und der anti ‐Form, wie Raman‐ und temperaturabhängige IR‐Spektroskopie in der Gasphase sowie in Ar‐Matrix, Gasphasen‐Elektronenbeugung und quantenchemische Berechnungen belegen 1_87. Die Synthese des Sulfuryldiazids O2S(N3)2 (Smp.…”