Spectra and structure of phosphorus-boron compounds, XII¹ Vibrational spectra and molecular symmetry of tetramethylbiphosphine-bisborane

Abstract

The infrared (200–3500 cm⁻¹) and Raman (50–3500 cm⁻¹) spectra of two isotopic species of tetramethylbiphosphine-bisborane, (CH₃)₄P₂·2BH₃ and (CH₃)₄P₂·2BD₃, in the solid state at low temperatures have been recorded. The spectra have been interpreted in detail on the basis ofC _2h molecular symmetry. The P-B stretching modes were assigned to bands at 599 and 567 cm⁻¹ in the Raman and infrared spectra of the “light” compound, respectively. Only one P-P stretching mode was observed in the Raman spectra. The vibrational data appear to be consistent with the presence of only one conformer in the solid state, which is at variance with the conclusions from an X-ray study. Considerable splitting of the low-frequency bending modes was observed for both compounds; this splitting has been attributed to the factor group.