Spectroscopic and Structural Studies of Difluorophosphoryl Azide F₂P(O)N₃, Difluorophosphoryl Isocyanate F₂P(O)NCO, and Difluorophosphoric Acid Anhydride, F₂(O)POP(O)F₂

Abstract

Difluorophosphoryl azide, F(2)P(O)N(3), was fully characterized by (19)F, (31)P, (14)N, and (15)N NMR, as well as by IR (gas, Ar-matrix), and Raman (liquid, solid) spectroscopy. For comparison the vibrational spectra of the isoelectronic difluorophosphoryl isocyanate, F(2)P(O)NCO was also studied. Both molecules were found to exist as single rotamers in the gas, liquid, and solid states. Their solid-state structures were determined by X-ray crystallography as the rotamers with the P=O bond being cis to the pseudohalide groups (with respect to the P-N bond). The F(2)P(O)N(3) molecule exhibits approximate C(s) symmetry (phi(O1P1-N1N2) = -0.7(3) degrees), while F(2)P(O)NCO is significantly distorted from C(s) symmetry (phi(O1P1-N1C1) = -18.9(5) degrees) because of intermolecular C...O contacts. The crystal structure of difluorophosphoric acid anhydride, F(2)(O)POP(O)F(2), was also determined, possessing crystallographic C(2) symmetry with the two F(2)PO groups slightly staggered by 10.66(7) degrees along the P...P vector, and a P-O-P angle of 140.89(10) degrees for the bridging oxygen atom. The experimental results are supported by quantum chemical calculations, and the conformational properties of F(2)P(O)N(3) and F(2)P(O)NCO are discussed.

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

“…In the IR spectra, the observed strongest bands at 2290 cm –1 (gas phase) and 2288.6 cm –1 (Ne matrix), belong to the antisymmetric stretching vibration of the NCO group [ν as (NCO)], which appears as a very weak band at 2283 cm –1 in the Raman spectrum. The band position is red‐shifted comparing to that of F 2 P(O)NCO (gas‐phase IR: 2309 cm –1 , Ar matrix IR: 2306.9 cm –1 , liquid Raman: 2307 cm –1 ), but it is blue‐shifted compared to that of OP(NCO) 3 (liquid IR: 2265 cm –1 ) . These shifts coincide with the electronegativity order F > Cl > NCO.…”

“…It is noteworthy that in the Raman spectrum of the liquid the P=O stretching vibration shifts to 1292 cm –1 , indicating the presence of intermolecular interactions including the phosphoryl oxygen atom in the condensed phase. The P–N stretching vibration (νPN) in Cl 2 P(O)NCO (747.1 cm –1 , Ne matrix) is slightly lower in frequency than that in F 2 P(O)NCO (751.8 cm –1 , Ar matrix) . The in‐plane and out‐of‐plane deformation modes of the NCO group in the Ne matrix are observed at 629.7 and 611.5 cm –1 , and the asymmetric and symmetric stretching vibrations of the ClPCl units in the liquid state occur at 597 and 517 cm –1 , respectively.…”

“…This indicates an interaction of the phosphoryl moiety P=O with the isocyanate group. The fluorinated analogue F 2 P(O)NCO only showed a very shallow minimum for the anti ‐conformer on an energy curve calculated at the B3LYP/6‐311+G(3df) level of theory. This implies that the fluorine atoms also affect the conformational properties, which can be attributed to steric reasons because the shorter P–F bond brings the fluorine atoms closer to the isocyanate group.…”

“…However, in contrast to other α‐oxo‐isocyanates, only very few simple phosphoryl isocyanates have been isolated and structurally characterized. Recently, the vibrational spectroscopy and solid‐state structure of the simplest phosphoryl isocyanate F 2 P(O)NCO have been reported . 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.…”

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

“…The structure of F 2 P(O)N 3 in the solid state occupies C s symmetry within the error range. [14] Concerning the geometrical parameters of the isocyanate group the NÀ C and CÀ O lengths are the same within error limits for the isocyanates bound to a phosphorus atom in the formal oxidation state + V. However, in the phosphorus(III) isocyanate Cl 2 PNCO [11] the NÀ C [b] ∡(NCO) [b] ∡(YÀ PÀ Y) [a] Distances r in Å, angles and dihedral angles in deg. [b] For the azides the analogous parameters are given.…”