Polarography in acetonitrile of some group-IV metal halides

Abstract

Summary The polarography and the conductance of solutions in acetonitrile of tin(IV) chloride and iodide, tin(II) chloride, and germanium(IV) and zirconium(IV) chlorides have been investigated. Tetraethylammonium perchlorate, chloride and iodide have been used as supporting electrolytes. With perchlorate the tetrahalides of tin and germanium yield two reduction waves, the first one corresponding to a two-electron reduction and the second wave to reduction to the metal. With chloride as supporting electrolyte only one four-electron reduction wave is observed, but two two-electron waves in iodide with tin(IV) and germanium(IV) chlorides. Tin(IV) iodide with tetraethylammonium iodide as supporting electrolyte yields a single, four-electron reduction wave, composite with the iodide wave. All compounds yield anodic waves which are poorly developed, probably because of film formation. Tin(II) chloride yields in the three supporting electrolytes an overall two-electron reduction wave. All waves appear to be irreversible and the anodic waves are of a complex nature. Contrary to the literature, zirconium tetrachloride in the presence of iodide and oxygen yields iodine, without reduction of zirconium(IV). Tin(IV) iodide reacts with chloride, the chloride replacing the iodide. From conductance data it is concluded that tin(IV) chloride and iodide dissociate into SnX3+ and X− ions, the ionization constants being 8×10−7 and 3.5×10−8, respectively. On the other hand, the dissociation of SnCl2 occurs mainly by the reaction: 2 SnCl2←SnCl++SnCl3− and to a lesser extent by the reaction SnCl2←SnCl++Cl−. The equilibrium constants for these two reactions were estimated to be 4×10−4 and 1.2×10−6, respectively.