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 Cd2I62– units interspaced with interacting I2 molecules arranged almost perpendicularly to the cadmium-containing layers. The Cd2I62– units consist of edge-sharing CdI4 tetrahedra. The I2 molecules have intramolecular distances ranging from 2.73 to 2.74 A and intermolecular distances ranging from 3.37 to 3.56 A. The I2-bridged Cd2I62– dimers create a network that can be described as infinite chains of I2 co-ordinated in a zigzag manner to the Cd2I62– 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 Cd2I62– units. The EXAFS of Cd (K shell) was determined for a 1∶10 mixture of CdI2–[Et3S][I7] confirming the structural relationship of CdII 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.