A Laser Raman Spectroscopic Study of Iodine Cations

Abstract

<p>I₂⁺Sb₂F₁₁⁻, a dark blue crystalline solid, was prepared by reaction of I₂ with SbF₅ using dried liquid SO₂ as solvent. The compound melts at 122°C and is moisture-sensitive. The presence of the I₂⁺ cation was established by laser Raman spectroscopy and by X-ray crystallography. The structure determination showed that the I₂⁺ cation has an I - I bond length of 2.557(4) Å.</p> <p>The triatomic cations I₃⁺, IBr₂⁺ and ICI₂⁺ were produced in acidic solutions and their Raman spectra were obtained using specially designed spinning Raman cells. IBr₂⁺ and ICI₂⁺ were also prepared as the solid compounds IBr₂⁺SO₃F⁻ and ICI₂⁺SbCl₆⁻ and their Raman spectra were recorded. A simple valence force field treatment was applied to the Raman data for these three symmetric IX₂⁺ cations. Force constants were calculated and the bond angles of the bent structures were estimated.</p> <p>The triatomic interhalogen cation I₂Cl⁺ was prepared by direct reaction of ICI and SbCl₅ to yield solid I₂Cl⁺SbCl₆⁻. By a similar halogen transfer process I₂Br⁺SbCl₅Br⁻ was prepared from IBr and SbCl₅. The Raman spectra of both of these dark-colored, low-melting solids were obtained using spinning cell techniques. Observation of Raman bands which could be assigned to a bending mode and to I - I and I - X stretching modes established that these two iodine-containing cations have an unsymmetric angular structure.</p> <p>The existence of a new polyatomic cation Inⁿ⁺ containing iodine in a +1 oxidation state is proposed. This species has a strong Raman band at 195 cm⁻¹. The Raman evidence indicates that Inⁿ⁺ exists in H₂SO₄ and HSO₃F solutions and also in solid or molten ISO₃F.</p>