DOROTHY J. BEARCROFT AND NORMAN H. NACHTRIEB
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Electrical Conductance of Salts in Liquid Iodine. 11. Iodide Acceptor Solutes1
by Dorothy J. Bearcroft and Norman H. Nachtrieb Institute for the Study of Metals and Department of Chemistry, The University of Chicago, Chicago, Illinois (Received May 22, 1967)
Electrical conductance measurements are reported for solutions of iodine monochloride, iodine monobromide, indium(II1) iodide, and gallium(II1) iodide in liquid iodine a t 140". The interhalogens cause a monotonic decrease in the solution conductance, while the metal iodide salts produce a deep minimum which is followed by a rapid rise in conductance. The results are interpreted in terms of a model in which iodine dissociates into If and polyiodide ions, whose high mobility is due to their ability to transfer iodide ions to iodine molecules. The interhalogens repress the ionization of the solvent by their own dissociation into I+ and X-. Indium(II1) iodide and gallium(II1) iodide behave as iodide ion acceptors, reacting with the solvent to form I+ and MI4- species. The latter behave like polyiodide ions in the charge transport process, but with lower apparent mobilities. Equilibrium constants for the dissociation of the interhalogens and for the reaction of the metallic iodides with the solvent are given.
Introduction I n an earlier publication2 we reported the results of a study of the electrical conductance of solutions of potassium iodide, thallium(1) iodide, silver iodide, and antimony(II1) iodide in liquid iodine a t 140". These solutions display the common characteristic of a monotonically increasing specific conductance with increasing salt' concentration. At very low solute concentration this dependence is linear, but positive deviations become apparent for concentrations exceeding several hundredths molar. Our interpretation was based upon the assumption that liquid iodine dissociates ionically and that the solute furnishes ions, ion pairs, and higher ion aggregates. The principal charge carrier was assumed to be the triiodide ion, 13-, or higher polyiodides, with the high mobility attributed to the rapid transfer of Iions from such anions to iodine molecules. The distinguishing property of these salts, as contrasted with those to be discussed in the present paper, is their high capacity to furnish I- ions to the solvent to form the highly mobile polyiodide species. I n the present paper, we report the results of an extension of this study to two different classes of solutes: The Journal of Physical Chemistry
(1) the interhalogens, IC1 and IBr, and ( 2 ) the iodide ion acceptor salts, Ga13 and In13. These two classes of solutes differ from one another and from the iodide ion donor salts (e.g., I
