Elgctron Density Distribution and Intramolecular Dynayics in Phosphorane (Cl3C)2PCl3

Abstract

The trigonal-bipyramidal structure of phosphorane (Cl₃C)₂PCl₃ (I) with two non-equivalent axial Cl₃C-groups at the P atom was established by the X-ray diffraction method. At 293°K these groups are involved in independent libration around the longest molecular axis and some characteristics of these motions were estimated from diffraction data. Electron density distribution in I was studied at 153°K (λMo, ca. 7000 reflections, “high-angle” refinement to R=0.027 using 1310 reflections with sinθ/λ ≥ 0.70 A°^?1). At low temperature tile above-mentioned independent librations of the Cl₃C-groups become frozen, which is proved by the rigid-body analysis of the anisotropic thermal parameters of I, and also by the NQR ³⁵Cl spectral data. All chemical bonds in I are characterized by peaks of positive deformation electron density (DED). Positive DED peaks are also found near C1-atoms and attributed to the lone pairs of C1-atoms. Elongation of the P-C bonds (2.000 (2) and 1.992 (2) A°) is caused by electrostatic repulsion of the positively charged P and C atoms, whose charges were estimated from diffraction data. The character of the electron density distribution in I is in accordance with the generally accepted notion on the nature of chemical bonds in pentacovalent phosphoranes.