On the Reaction of Phosphorous Acid with Superacids and the Crystal Structure of H(5)O(2)(+)SbF(6)(-) and Me(4)N(+)HPF(5)(-).

Abstract

Phosphorous acid reacts with the superacidic system HF/SbF(5) with formation of HPF(4), water, and oxonium hexafluoroantimonate, which crystallizes as H(5)O(2)(+)SbF(6)(-) in the triclinic space group P&onemacr; with a = 6.492(6) Å, b = 7.469(8) Å, c = 8.095(6) Å, alpha = 116.17(7) degrees, beta = 93.90(7) degrees, and gamma = 112.34(7) degrees, with two formula units per unit cell. The unit cell contains two H(5)O(2)(+) ions of approximate symmetry C(2)(h)() with an intramolecular O.O distance of 2.418(8) or 2.40(1) Å, respectively. The reaction is discussed with regard to the formation of protonated species in various superacidic media. In addition the crystal structure of Me(4)N(+)HPF(5)(-) which is formed by the reaction of HPF(4) with Me(4)N(+)F(-) is reported. The salt crystallizes in the tetragonal space group P4/nmm with a = 8.564(5) Å and c = 5.687(2) Å, with two formula units per unit cell. The P-F distances of P-F(eq) = 1.595(6) Å and P-F(ax) = 1.594(9) Å for the psi-octahedral HPF(5)(-) show no significant interaction exercised by hydrogen on the cis- and trans-fluorine.