Studies on peroxomolybdates. XV. Crystal structure of ammonium difluorooxodiperoxomolybdate(VI), (NH4)2[MoF2O(O2)2], and a survey of important distances in pentagonal-bipyramidal peroxomolybdates

Abstract

The crystal structure of ammonium difluorooxodiperoxomolybdate(VI), (NH4)2[MoF2O(O2)2], has been determined by single-crystal X-ray diffraction methods. The yellow compound crystallizes in the triclinic space groupP¯1 witha=7.752(2),b=7.498(3),c=6.066(2) A,α=86.37(3),β=109.60(3),γ=94.45(3)°, andZ=2. A total of 3857 reflexion intensities was recorded on a SyntexP21 diffractometer using MoKα radiation at room temperature. The structure was solved by the Patterson method and successive electron density calculations. Full-matrix least-squares refinement yielded a finalR value of 0.027 for 3729 observed [I>3σ(I)] reflexions. In the complex anion molybdenum is surrounded by a pentagonal-bipyramidal arrangement of ligand atoms. Two side-on bonded peroxo groups and a fluorine atom form the equatorial plane and one fluorine atom and a double-bonded oxygen atom occupy the apical positions. The molybdenum atom is displaced 0.311(1) A from the equatorial plane in the direction of the double-bonded oxygen atom. Bond distances: Mo-Operoxo 1.931(2)-1.976(2) A, Mo=Oapical 1.688(2) A, Mo-Fequatorial 1.979 (1) A, Mo-Fapical 2.199(1) A and (O-O)peroxo 1.474(2)-1.480(2) A.