Construction of Ternary Iodine-Bromine-Chlorine Octahalides

A series of five ternary octanuclear iodine-bromine-chlorine interhalides, [I₂ Br₂ Cl₄ ]^2- (1), [I₃ BrCl₄ ]^2- (2), [I₄ Br₂ Cl₂ ]^2- (3), [I₂ Br₄ Cl₂ ]^2- (4) and [I₃ Br₃ Cl₂ ]^2- (5), have been rationally constructed in two steps. Firstly, addition of a dihalogen (ICl or IBr) to the triaminocyclopropenium chloride salt [C₃ (NEt₂ )₃ ]Cl forms the corresponding trihalide salt with [ICl₂ ]^- or [BrICl]^- anions, respectively. Secondly, addition of a half-equivalent of a second dihalogen, followed by crystallization at low temperature, gives the corresponding octahalide: addition of Br₂ and IBr to [ICl₂ ]^- gives 1 and 2, respectively, whereas addition of I₂ , Br₂ and IBr to [BrICl]^- gives 3, 4 and 5, respectively. The five octahalides were characterized by X-ray crystallography and far-IR spectroscopy.