The Binary Iodine-Chlorine Octahalide Series [I_n Cl_8-n ]^2- (n=3, 3.6, 4)

The octanuclear iodine-chlorine interhalides [I₄ Cl₄ ]^2- and [I₃ Cl₅ ]^2- were prepared in two steps. Firstly, addition of ICl to the triaminocyclopropenium chloride salt [C₃ (NEt₂ )₃ ]Cl forms the trihalide ICl₂ ^- salt, secondly, addition of half an equivalent of I₂ or ICl, respectively, gave the desired products upon crystallization at low temperature. The non-stoichiometric octahalide [I_3.6 Cl_4.4 ]^2- was obtained after heating a CH₂ Cl₂ solution of the ICl₂ ^- salt to reflux for 2 hours followed crystallization. [I₄ Cl₄ ]^2- is best described as two ICl₂ ^- anions bridged by I₂ , whereas [I₃ Cl₅ ]^2- is best described as an [I₂ Cl₃ ]^- pentahalide with a weak halogen bond to an ICl₂ ^- trihalide. The octahalides were characterized by X-ray crystallography, computational studies, Raman and Far-IR spectroscopies, as well as by TGA and melting point.