N(CH3)(4)(PF4-)-P-+, the first example of a PF4- salt, has been prepared from N(CH3)(4)F and PF3 using either CH3CN, CHF3, or excess PS as a solvent. The salt is a white, crystalline solid which is thermally stable up to 150 degrees C, where it decomposes to N(CH3)(3), CH3F, and PF3. The structure of;the PF4- anion was studied by variable temperature P-31 and F-19 NMR spectroscopy, infrared and Raman Spectroscopy, SCF, MP2, local and nonlocal density functional calculations, a normal coordinate analysis, and single-crystal X-ray diffraction. The anion possesses a pseudo trigonal bipyramidal structure with two longer axial bonds and an equatorial plane containing two shorter equatorial bonds and a sterically active free valence electron pair. In solution, it undergoes an intramolecular exchange process by the way of a Berry pseudorotation mechanism. The vibrational frequencies observed for PF4- in solid N(CH3)(4)PF4 are in excellent agreement with those calculated for free gaseous PF4-. The X-ray diffraction study (tetragonal, space group P42(1)m, a = 8.465(3) Angstrom, c = 5.674(2) Angstrom, Z = 2, R = 0.0723 for 268 observed [F greater than or equal to sigma(F)] reflections suffers from a 3-fold disorder with unequal occupancy factors for the equatorial fluorine atoms of PF4- but confirms its pseudo trigonal bipyramidal structure and the axial P-F bond length calculated for the free ion.
