Investigations of the polyiodides H3O·Ix (x = 3, 5 or 7) as dibenzo-18-crown-6 complexes

Abstract

The compounds [H₃O(dibenzo-18-crown-6)][I_x] (x = 3,5,7) have been synthesised and investigated by X-ray diffraction as well as Raman and far-IR spectroscopy. The structure of the triiodide contains two independent, slightly asymmetric and bent I₃⁻ ions with I–I distances in the range 2.92–2.94 Å. The pentaiodide can be described as composed of (I₃⁻)·I₂, where the I–I distances in the asymmetric and slightly bent I₃ unit are 2.894(2) and 2.942(2) Å and in the I₂ unit 2.763(2) Å. The L-shaped I₅⁻ ions are linked together forming a chain of I₁₀ rectangles through van der Waals interactions in the range 3.7–3.8 Å. The structure determination supports a pyramidal geometry of the H₃O⁺ ion in the dibenzo-18-crown-6 moiety of both structures. Because of severe crystal twinning the crystal structure of the heptaiodide could not be determined. However, the results from the spectroscopic investigation are consistent with a heptaiodide of composition (I₃⁻)·2I₂.