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

摘要

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 I-3(-) ions with I-I distances in the range 2.92-2.94 Angstrom. The pentaiodide can be described as composed of (I-3(-)). I-2, where the I-I distances in the asymmetric and slightly bent I-3 unit are 2.894(2) and 2.942(2) Angstrom and in the I-2 unit 2.763(2) Angstrom. The L-shaped I-5(-) ions are linked together forming a chain of I-10 rectangles through van der Waals interactions in the range 3.7-3.8 Angstrom. 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 (I-3(-)). 2I(2). [References: 49]