The molecular structures of gaseous tetrafluorohydridophosphorane, HPF4, and trifluorodihydridophosphorane, H2PF3, as determined by electron diffraction

Abstract

The structures of gaseous tetrafluorohydridophosphorane, HPF₄, and trifluorodihydridophosphorane, H₂PF₃, have been determined by electron diffraction. The results indicate that both molecules adopt structures based on a trigonal bipyramid centred on the phosphorus atom, with the hydrogen atoms occupying equatorial sites, in conformity with C_2v symmetry. Salient structural parameters (r_a) are: (i) for HPF₄, r(P–F_eq) 153.7(0.4), r(P–F_ax) 159.1 (O.4), and r(P–H) 132.4(4.6) pm; H–P–F_eq 123.0(0.9) and H–P–F_ax 87.8(0.2)°; (ii) for H₂PF₃, r( P–F_aq) 154.4(0.4), r(P–F_ax) 161.3(0.2), and r( P–H) 132.2(1.1 ) pm; H–P–F_eq 119.6(4.4) and F_eq–P–F_ax 91.7(0.2)°. Replacement of fluorine by hydrogen thus results in unusually short P–H bonds, attenuation of the apical P–F bonds, and distortion of the PF_n fragment (n= 4 or 3) so that the apical P–F bonds are bent towards, while the equatorial P–F bonds in HPF₄ are bent away from, the hydrogen substituents.