Crystallographic, Spectroscopic and Theoretical Studies of Fluoro- Kr(II), Xe(ID, Au(V) and Halogen(VII) Compounds; and New Synthetic Developments in Bromine(VII) Oxide Fluoride Chemistry

Abstract

<p>The structures of a-KrF2, [KrF][W'6] (M = As, Sb, Bi, Au) and several salts containing the Kr₂F₃⁺ cation have been determined by use of low-temperature single-crystal X-ray diffraction. These structures account for nearly all of the crystallographic work reported for Kr(ll) compounds, and represent the first studies of heir kind for salts containing the KrF⁺ and Kr₂F₃⁺ cations. The crystallographic characterization of the strongly fluorine bridged [KrF][MF₆] ion pairs prompted a more comprehensive survey of XeF⁺ salts, which included the X-ray structure determinations of [XeF][MF₆] (M = As, Sb, Bi), and [XeF][M2FU] (M = Sb, Bi). Variations in the Ng--Fb (Ng = Kr, Xe) bridge bond lengths of the NgF+ salts were used to assess the relative fluoride ion acceptor strengths of AsF 5, SbF 5, BiP 5, AuF 5, Sb2F 10 and BhF 10 and the results were compared with a recently reported Lewis acidity scale derived from electronic structure calculations. The potent oxidizer properties of the KrF+ cation have been used to synthesize [02][AuF6] by the reaction of [KrF][AuF6] with 02. A previously unknown and ordered phase of [02][AuFd was identified by variable temperature Raman spectroscopy and by single- crystal X-ray diffraction, and resulted in the reassignment of the V2(Eg} vibrational mode of AuF6-. The limited chemistry of Br(W) has been extended in several respects. Accurate geometric parameters for the previously known BrF6 + cation and its chlorine and iodine analogues have been determined by single-crystal X-ray diffraction, allowing bond length trends among the late period 3 - 5 hexafluoro-species to be established. The octahedral geometries of the XF6 + (X = CI, Br, I) cations in solution have been confirmed by the measurement of their 35,370, 79,81Br an.d 1271 NMR spectra an.d spin.-Iattice relaxation times (T1) in HF solution. The previously un.1rnown. fluoride ion acceptor properties of Br03F have been established by its reaction.s with [N(CH3)4][F], CsF, RbF, KF an.d NOF. The resulting Br03F2- anion is only the fourth example of a Br(VTI) species, with its predicted D3h symmetry having been. confirmed by vibration.al spectroscopy, 19F NMR spectroscopy, single-crystal X-ray diffraction an.d electronic structure calculations. The internal and symmetry force constants of Br03F2- have been determined and are compared with the isostructural species Xe03F2, Os03F2 and CI03F2-. The stronger fluoride ion. acceptor properties of Br03F relative to those of CI03F have been demonstrated by use electronic structure calculations and have helped to explain. failed attempts to prepare the 003F2- anion. The fluoride ion. don.or properties of Br03F and CI03F were investigated by their reactions with SbF5(l). Whereas CI03F does not react with SbFs(l), Br03F undergoes reductive elimination of 02 to form [Br02] SbnFsn+l]. The geometric parameters of the Br02 + cation have been obtained for the first time in the solid state by the X-ray structure determination of [Br02][SbF6]. The contrasting reactivities ofBr03F and CI03F towards (SbFs)n have been addressed by use ofthermochemical calculations. Attempts to prepare Br01F3 or salts containing the Br01Ft cation by ligand exchange reactions with Br03F and oxidative fluorination of Br02F were unsuccessful, but have been accounted for by use of electronic structure calculations which were employed to evaluate the thermochemistries of the attempted reactions.</p>