A general method is described that allows experimental equilibrium structures to be determined from gas electron diffraction (GED) data. Distance corrections, starting values for amplitudes of vibration and anharmonic "Morse" constants (all required for a GED refinement) have been extracted from molecular dynamics (MD) simulations. For this purpose MD methods have significant advantages over traditional force-field methods, as they can more easily be performed for large molecules, and, as they do not rely on extrapolation from equilibrium geometries, they are highly suitable for molecules with large-amplitude and anharmonic modes of vibration. For the test case Si(8)O(12)Me(8), where the methyl groups rotate and large deformations of the Si(8)O(12) cage are observed, the MD simulations produced results markedly superior to those obtained using force-field methods. The experimental equilibrium structure of Si(8)O(12)H(8) has also been determined, demonstrating the use of empirical potentials rather than DFT methods when such potentials exist. We highlight the one major deficiency associated with classical MD--the absence of quantum effects--which causes some light-atom bonded-pair amplitudes of vibration to be significantly underestimated. However, using C(3)N(3)Cl(3) and C(3)N(3)H(3) as examples, we show that path-integral MD simulations can overcome these problems. The distance corrections and amplitudes of vibration obtained for C(3)N(3)Cl(3) are almost identical to those obtained from force-field methods, as we would expect for such a rigid molecule. In the case of C(3)N(3)H(3), for which an accurate experimental structure exists, the use of path-integral methods more than doubles the C-H amplitude of vibration.

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(C2F5)2PNEt2 represents an excellent starting material for the selective synthesis of bis(pentafluoroethyl)phosphane derivatives. The moderately air‐sensitive aminophosphane is accessible on a multi‐gram scale by treating Cl2PNEt2 with C2F5Li. Treatment with gaseous HCl or HBr yielded the corresponding phosphane halides (C2F5)2PCl and the so far unknown (C2F5)2PBr in good yields. The hitherto unknown (C2F5)2PF was obtained by treating (C2F5)2PBr with excess antimony trifluoride. Treatment of (C2F5)2PCl with Bu3SnH led to the quantitative formation of (C2F5)2PH. Deprotonation formally yielded the (C2F5)2P– anion in a form that was stabilized by coordination to mercury ions to form the complex [Hg{P(C2F5)2}2(dppe)]. An improved high‐yielding synthesis of (C2F5)2POH was achieved by treating (C2F5)2PNEt2 with p‐toluenesulfonic acid. The gas‐phase structures of (C2F5)2PH and (C2F5)2POH were determined by electron diffraction. The vibrational corrections employed in the data analysis of the diffraction data were derived from molecular dynamics calculations. Both compounds exist in the gas phase mostly as C1‐symmetric cis,cis conformers with regard the orientation of the C2F5 groups relative to the functional groups H and OH. The presence of a second conformer at ambient temperature is likely in both cases. The refined amounts of dominant conformers are 94(6) and 85(6) % for (C2F5)2PH and (C2F5)2POH, respectively. The conformational behaviour was further explored by potential energy surface scans based on DFT calculations. Important experimental structural parameters for the most stable conformers are re(P–C)average = 1.884(3) Å for (C2F5)2PH and re(P–C)average = 1.894(4) Å and re(P–O) = 1.582(3) Å for (C2F5)2POH. The different coordination properties of (C2F5)3P, (C2F5)2POH, (CF3)3P and (CF3)2POH were evaluated by complex formation with [Ni(CO)4]: the maximum achievable number of CO ligands substituted by (C2F5)3P is 1, by (C2F5)2POH is 2, by (CF3)3P is 3 and by the smallest ligand (CF3)2POH is 4.