Metal iodides in polyiodide networks. The structural chemistry of CdI2 with an excess of iodine*

Abstract

The reaction between [Me₃S][I₅] and CdI₂ at 80 °C resulted in the compound [Me₃S][Cd₂I₆]_1/2·3I₂, which has been characterised by X-ray diffraction, Raman spectroscopy and EXAFS. The structure consists of layers of I₂-bridged, dimeric Cd₂I₆^2– units interspaced with interacting I₂ molecules arranged almost perpendicularly to the cadmium-containing layers. The Cd₂I₆^2– units consist of edge-sharing CdI₄ tetrahedra. The I₂ molecules have intramolecular distances ranging from 2.73 to 2.74 Å and intermolecular distances ranging from 3.37 to 3.56 Å. The I₂-bridged Cd₂I₆^2– dimers create a network that can be described as infinite chains of I₂ co-ordinated in a zigzag manner to the Cd₂I₆^2– dimers, interspaced by formal I₁₀ units. The Raman spectrum is dominated by a peak at about 185 cm^–1, which confirms the charge-transfer interaction of I₂ with the Cd₂I₆^2– units. The EXAFS of Cd (K shell) was determined for a 1∶10 mixture of CdI₂–[Et₃S][I₇] confirming the structural relationship of Cd^II in the liquid reaction medium and the isolated polyiodide compound. For comparison, the crystal structures of iodine-free [Et₃S][Cd₂I₆]_1/2 and two phases of polymeric [Me₃S][CdI₃] were also determined.