| Abstract
| - The Me4PF has an ionic structure in the solid with a weakly coordinated fluoride ion and it can be considered as a source for the “naked” fluoride. It possesses unique properties compared to the known sources for the naked fluoride due to its volatility in a vacuum. Gaseous Me4PF has a trigonal-bipyramidal structure with an exceptionally long P−Fax bond. It is also the first example of a phosphorane with an axial methyl group.
- Me4PF was investigated in the solid state, in the gas phase, and in solutions. Vibrational spectra of the solid anda single-crystal structure show an ionic tetramethylphosphonium fluoride. The compound crystallizes in the spacegroup Pbca with a = 1016.0(1), b = 1018.0(1), c = 1205.8(4) pm, and Z = 8. The fluoride ion is nearly trigonalplanar surrounded by three Me4P+ cations forming six H···F contacts between 218 and 240 pm. The compoundis stable below 120 °C and sublimes in a vacuum. It possesses a phosphorane structure in the gas phase that wasstudied by electron diffraction and vibrational spectra, and additionally by theoretical calculations. The Me4PF moleculehas a trigonal bipyramidal structure with one methyl group and the fluorine atom in axial positions and bondlengths of d(PCeq) = 182.6(4) pm, d(PCax) = 188.4(8) pm, and d(PF) = 175.3(6) pm. The compound is remarkablysoluble in acetonitrile, water, and alcohols, and slightly soluble in benzene, dimethyl ether, and diethyl ether. Thesolutions were studied by 1H, 13C, 19F, and 31P NMR spectroscopy. The hygroscopic Me4PF forms a tetrahydratewhich crytallizes in the space group I41/a with a = 1106.1(1) pm, c = 816.3(1) pm, and Z = 4. The fluoride ionin Me4PF·4 H2O is surrounded by four water molecules. These units form a three-dimensional network in which theMe4P+ cations are embedded without any contacts.
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