Spectroscopic Studies of Antimony III and V Halide Complexes

Abstract

<p>Antimony-121 Mössbauer spectra have been recorded at liquid-helium temperatures for a number of complex anions derived from SbF₃: M₂[SbF₅] (M₂ = Na₂, K₂, or N₂H₆); NaSbF₄; M[SbClF₃] (M = K or NH₄); Na[SbClF₃]·H₂O; M[Sb₃F₁₀] (M = Na, T1, or NH₄); M[Sb₄F₁₃] (M = K or Cs); and [NH₄]₄[Sb₅F₁₉]. The data were consistent with the known stereo-chemistry of these compounds in which the anitmony 5s electron pair is stereochemically active in a distorted AX₆E environment with a 3:3:1 arrangement or monocapped octahedron, the lone pair in the 1 position.</p> <p>The ¹²¹Sb Mössbauer spectra of a number of [SbX⁻₄] (X = Cl, Br, or I) and [Sb₂X₉³⁻] (X = F, Cl, Br, or I) salts have been reported. Only [Sb₂F₉³⁻] shows a significantly large quadrupole splitting with the 5s electrons being stereochemically active.</p> <p>The nature of the compounds of the series SbCl₅₋ᵪFᵪ have been in dispute in the literature for several years, but only SbCl₄F, which has been identified as a cis-fluorine bridged tetramer, and "SbCl₂F₃", which has been shown to exist with the ionic formulation [SbCl₄⁺][Sb₂Cl₂F₉⁻], are well characterized. It was found in this work that a fluorine bridged [SbCl⁺₄][Sb₂Cl₂F₉⁻] species in the solid state is more consistent with the chemistry of this compound. The previously unknown Sb₃Cl₁₀.₇₅F₄.₂₅ was prepared and found from X-ray crystallography to exist as a disordered cis-fluorine bridged trimer in the solid state. SbCl₃F₂ was prepared and characterized as a cis-fluorine bridged tetramer in the solid state. An attempt to prepare SbClF₄ always resulted in the formation of [SbCl⁺₄][Sb₂F₁₁⁻], which previously had been little studied. These SbCl₅₋ᵪFᵪ compounds have been characterized using Mössbauer and Raman spectroscopy, and Mass spectrometry. The reaction of SbCl₄F with strong Lewis acids was also investigated. SbCl₄F was found to form [AsCl₄⁺]-[SbF⁻₆] with AsF₅, [SbCl₄⁺][Sb₂Cl₂F⁻₉] with SbF₅, and a polymeric complex of the type [SbCl₄F.(NbF₅)ᵪ] (x = 1, or 2) with NbF₅.</p> <p>The reaction of alkali metal halides with antimony(V) halides in liquid SO₂ at room temperature yielded the salts: M[SbCl₆] (M = Na or K); Na[SbCl₄F₂]; Na[SbCl₂F₄]; and M[SbF₆] (M = K or Cs). The variation of ¹²¹Sb Mössbauer isomer shifts and quadrupole coupling constants are discussed in terms of molecular geometry. The salt Na[SbCl₄F₂] has been shown by Raman spectroscopy to exist as the trans isomer in the solid state.</p> <p>Mössbauer data are reported for pure SbF₅ and SbCl₅, and when intercalated into graphite the spectra show that these halides do not enter the graphite lattice without some reduction to Sb(III) occurring.</p> <p>Data are reported for a number of SbF₅·X adducts, where X represents SbF₃, AsF₃, or SO₂ at 4ºK. The Mössbauer parameters of SbF₅·SbF₃ (type A), and the SbF₅-SbF₃ 1:1 adduct, [Sb₂F²⁺₄][SbF₆⁻]₂, do not support the contention that these forms are identical.</p> <p>The complex anions of [Te₂Se₂²⁺][Sb₃F₁₄⁻][SbF₆⁻] and [Te₃.₃Se₀.₇²⁺]-[Sb₃F₁₄⁻][SbF₆⁻] have also been investigated by the Mössbauer method. The magnitude of the n values calculated for the Sb(III) sites are interpreted in terms of the varying asymmetry about the principle axis, which passes through the lone pair of electrons.</p>