The vibrational spectra and molecular structures of difluoro(isocyanato)phosphine and difluoro(isothiocyanato)phosphine in the gas phase

Abstract

The i.r. and Raman spectra of difluoro(isocyanato)phosphine, F₂PNCO, and difluoro(isothiocyanato)phosphine, F₂PNCS, have been recorded. Assignments have been made of all the fundamental frequencies, and normal coordinate analyses have been carried out. Mean amplitudes of vibration and perpendicular amplitude correction coefficients have been derived from the spectroscopic data. The molecular structures of the two compounds have been used to determined by the sector-microphotometer method of electron diffraction, and the spectroscopic data have been used to determine average interatomic distances. The principal parameters (r_a) for F₂PNCO are: r(P–F) 1·563 ± 0·003, r(P–N) 1·683 ± 0·006, r(N–C) 1·256 ± 0·006, r(C–O) 1·168 ± 0·005 Å; ∠(P–N–C) 130·6 ± 0·8°. For F₂PNCS the parameters are: r(P–F) 1·566 ± 0·003, r(P–N) 1·686 ± 0·007, r(N–C) 1·221 ± 0·006 Å; ∠(P–N–C) 140·5 ± 0·7°. In each case the pseudohalide group is approximately trans to the bisector of the FPF angle, with the molecules possessing overall C_s symmetry.