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

The reaction between [Me2S][I-5] and CdI2 at 80 degrees C resulted in the compound [Me3S][Cd2I6](1/2). 3I(2), which has been characterised by X-ray diffraction, Raman spectroscopy and EXAFS. The structure consists of layers of I-2-bridged, dimeric Cd2I62- units interspaced with interacting I-2 molecules arranged almost perpendicularly to the cadmium-containing layers. The Cd2I62- units consist of edge-sharing CdI4 tetrahedra. The I-2 molecules have intramolecular distances ranging from 2.73 to 2.74 Angstrom and intermolecular distances ranging from 3.37 to 3.56 Angstrom. The I-2-bridged Cd2I62- dimers create a network that can be described as infinite chains of I-2 co-ordinated in a zigzag manner to the Cd2I62- dimers, interspaced by formal I-10 units. The Raman spectrum is dominated by a peak at about 185 cm(-1), which confirms the charge-transfer interaction of I-2 with the Cd(2)I(6)(2-)units. The EXAFS of Cd (K shell) was determined for a 1:10 mixture of CdI2-[Et2S][I-7] 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.