Molekülstrukturen von Phosphorverbindungen, IV / Molecular Structures of Phosphorus Compounds, IV

Abstract

The molecular structures of the two trifluoromethyl phosphoranes (CF3)2PCl3 and (CF3)3PCl2 have been determined by electron diffraction of gases. The structure of (CF3)2PCl3 was found to be a regular trigonal bipyramid with both CF3 groups in axial positions (D3h symmetry) and the fluorine atoms staggered to the equatorial chlorine atoms. The following geometric parameters (ra-values) were obtained: r(C-F) = 1.331(2) Å, r(P-C) = 1.950(II) Å, r(P-Cl) = 2.036(2) Å and ⦓ FCF = 108.3°(0.4). (CF3)3PCl2 possesses the structure of a distorted trigonal bipyramid with two CF3 groups in axial and one in equatorial position. Again the fluorine atoms of the axial CF3 groups are staggered to the equatorial atoms. The ra-values for the geometric parameters are: r(C-F)= 1.329(2) Å, r(P-C)eq= 1.938(31) Å, r(P-C)ax = 1.946(14) Å, r(P-Cl) = 2.053(6) Å, ⦓ FCF = 108.5°(0.3), ⦓ ClPCl = 133.0°(1.7) and ⦓ CaxPCeq = 95.5°(1.9). The average P-C bond length was found to be r(P-C)av = 1.943(5) A. The results for the mean square amplitudes are given in the article. It was shown that in both molecules the torsional amplitudes of the CF3 groups around the P-C bond directions are small, indicating high potential barriers to internal rotation.