The structure of room temperature molten polyiodides

Abstract

The structure of molten polyiodides, Et₃SI _x (l) (Et = ethyl; x = 3, 4, 5 and 7), have been investigated by liquid x-ray scattering and Raman spectroscopy techniques at room temperature. The predominant iodine-containing species in Et₃SI₃(l) is a centrosymmetric I₃ ^- ion with a closest I-I distance of 2·915(2) Å. The Raman spectra indicate a large bond flexibility of the triiodide ion. The structural results of the iodine-rich melts Et₃SI _x (l), x > 3, are consistent with a three-dimensional network of interconnected I₃ ^- ions and I₂ molecules. The short-range order bears close similarities to that of pure liquid and solid iodine. The triiodides are on the average solvated by one, two and three iodine molecules for x = 4, 5 and 7, respectively. The coordination mode is flat-on with the I₃ ^- and I₂ units almost parallel but slightly tilted away from each other like the nearest-neighbour contacts in pure iodine. Previously published conductivity results are consistent with such a structure model.