Microwave Spectrum, Structure, and Dipole Moment of Difluorophosphine Borane

Abstract

The structure of difluorophosphine borane (HF2P☒BH3) has been determined from the microwave spectra of six isotopic species. The expected staggered conformation and CsCs symmetry have been confirmed. The structural parameters are: d(PH) = 1.409 ± 0.004Å;d(PF) = 1.552 ± 0.006Å;d(PB) = 1.832 ± 0.009Å;d(BHa) = 1.226 ± 0.005Å;d(BHs) = 1.200 ± 0.007Å;∠HaBHa = 112.7 ± 0.5°;∠HaBHs = 115.9 ± 0.4°;∠FPF = 100.0 ± 0.5°;∠FPH = 98.62 ± 0.25°;∠BPF = 117.7 ± 0.3°d(PH)=1.409±0.004Å;d(PF)=1.552±0.006Å;d(PB)=1.832±0.009Å;d(BHa)=1.226±0.005Å;d(BHs)=1.200±0.007Å;∠HaBHa=112.7±0.5°;∠HaBHs=115.9±0.4°;∠FPF=100.0±0.5°;∠FPH=98.62±0.25°;∠BPF=117.7±0.3°. Two angles (PBHs = 109.9 ± 0.3°;PBHa = 99.89 ± 0.26°)(PBHs=109.9±0.3°;PBHa=99.89±0.26°) indicate a tilt of the borane group away from the fluorine atoms. The value of the dipole moment obtained from Stark splittings is 2.504 ± 0.030 D. A range for the barrier to internal rotation is estimated as 3600–4500 cal/mole. The change in structural parameters of HF2PBH3 compared to similar compounds, the stability of HF2PBH3 towards dissociation, and the tilted borane group are discussed