Synthesis and Crystal Structure of Diiodine(Ⅴ/Ⅶ) Hexaoxide: An Intermediate between a Molecular and a Polymer Solid

摘要

Exploring the field of binary halogen oxides has always been a task of particular intricacy. Except for I_2O_5, which is well established, all oxides of the halogens are thermodynamically unstable. Therefore, it is not surprising that, in spite of almost 200 years of investigation, our knowledge about this important class of inorganic compounds remained rather fragmentary. Recently, significant progress has been achieved in understanding the chemistry of the oxides of chlorine and bromine. In contrast, the situation for the oxides of iodine has barely improved, so far. In the literature or even in textbooks numerous oxides of iodine are mentioned which in general are not properly confirmed. In many instances the compositions given are questionable because of preparative problems, and the proposed structures are speculative because of the lack of reliable and unambiguous experimental spectroscopic or X-ray data. Iodine oxides are usually prepared from complex mixtures, are polymeric in structure, and are thermally labile. Many experimental parameters have to be controlled precisely, and the formation of well-defined solid phases is often ruled by solubility differences. Thus, reproducible syntheses of iodine oxides as crystalline, pure samples are a real challenge.