Synthesis, Structure and Bonding in Polyiodides and Binary Metal Iodide-Iodine Systems

Abstract: Polyiodides and binary metal iodide-iodine compounds have been prepared and investigated by means of X-ray diffraction, EXAFS, far-IR, Raman, UV-vis and NMR spectroscopy and quantum chemical calculations. (Et3S)[AuI4].2I2 and (Me3S)[Cd2I6]1/2.3I2 were synthesised through the reaction between the room temperature melt of trialkylsulfonium polyiodides and the corresponding metal iodides. The structure of (Et3S)[AuI4].2I2 consists of AuI4- units coordinated by I2 forming infinite zigzag chains, while (Me3S)[Cd2I6]1/2.3I2 has a network structure. [hmtH]2(Hg2I6)1/2(HgI3).1/2I2, stable at ambient conditions, was made through the reaction between hmt.HgI2 and HI. The structure consists of infinite linear chains of iodine coordinated to the bridging iodide of Hg2I62-. Raman and far-IR spectra of the binary metal iodide-iodine compounds show features in the 180 cm-1 region characteristic for charge-transfer coordinated iodine. The polyiodide (Me3S)3I26 was prepared by the reaction between TlI and (Me3S)I7. The structure consists of a complicated network. A spectroscopic and quantum chemical study of the trialkylsulfonium polyiodide reaction medium indicate that the spectral features can be explained by the presence of both asymmetric and symmetric triiodides and a small amount of higher polyiodides formed by the decomposition of the triiodide. These results were also supported by the spectroscopic and structural investigation of dibenzo-18-crown-6 polyiodides and mixed polyhalides. A quantum chemical study of polyiodides and gold iodides shows that they are closely related and that AuI2- and AuI4- are appropriate guest molecules in polyiodide structures. A structural statistical and quantum chemical investigation of the intermolecular bonding in polyiodides indicate that these are best characterised as weak covalent bonds. (DodMe2)SI has a bilayered structure which indicate potential use as medium for inorganic liquid crystals based on the corresponding polyiodides.