The Binary Iodine‐Chlorine Octahalide Series [I_nCl_8−n]²⁻ (n=3, 3.6, 4)

Abstract

The octanuclear iodine‐chlorine interhalides [I4Cl4]2− and [I3Cl5]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 [I3.6Cl4.4]2− was obtained after heating a CH2Cl2 solution of the ICl2− salt to reflux for 2 hours followed crystallization. [I4Cl4]2− is best described as two ICl2− anions bridged by I2, whereas [I3Cl5]2− is best described as an [I2Cl3]− 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.

Construction of Ternary Iodine–Bromine–Chlorine Octahalides

“…As with the binary octahalides reported earlier, [7,16] salts 1-5 crystallize readily from CH 2 Cl 2 /diethylethers olutions at low temperature and all of the salts form in the monoclinic C2/m space group with one cation and half ad ianion in the asymmetric unit. The octahalide sits on ac rystallographic inversion center and lies in am irror plane;t he trans Z-configuration is typical of octahalides.E ach octahalide is sandwiched by two cations,i na ddition to weaker interactions with other cations.…”

“…[7,16] The non-stoichiometric octahalide [I 3.6 Cl 4.4 ] 2À wasa lso isolated. [7] It is key in this process to recognize the thermodynamically-preferred positions for each halogen:t he moste lectropositive atoms prefer the central position of the trihalide units followed by the central dihalogen atom positions with the terminalt rihalide positions beingp referred by the more electronegativea toms.T his also follows the sequenceo ff ormal oxidations states: + 1, 0a nd À1. Any other arrangementw ould be unstable, and to date we have not observed such as pecies.…”

“…[2] Haller and Riedel define classical interhalides, such as [IBr 2 ] À and [ICl 4 ] À ,a s containing ac entral electropositive atom with electronegative substituents, andn on-classical interhalides, such as [Cl(I 2 ) 4 ] À and [I 4 Cl 4 ] 2À ,a st hose which contain halogen bonding; [2] in those cases, Cl À and [ICl 2 ] À ,r espectively,d onatet ot he sigma hole of I 2 . [7,8] Interestingly,t he number of confirmed (by X-ray diffraction) ternary interhalides to date has been limited to one example,t he classical [BrICl] À trihalide. [9,10] Yagi andP opov claimed the synthesis of the pentahalide [I 2 Cl 2 Br] À by the reaction of [ICl 2 ] À with IBr or [BrICl] À with ICl, which seem reasonable syntheses;h owever,t here is no structural reporta nd only one IR band (at 294 cm À1 )w as reported.…”

“…[11] As imilar claim for the [ClI 4 ] À pentahalide has been shown to be am ixture of [I 5 ] À and [ICl 2 ] À . [7,12] In 1937, Ray and Mazumdar reported the ternary interhalide [NEt 4 ][IBrCl 3 ], which was prepared by treatment of I 2 Cl 6 with [NEt 4 ]Br.I ti sl ikely that this is ac lassical interhalide containing ac entral Ia tom with as quare planar geometry; however,a gain,t he characterization was very limited. [13] The ternary interhalogen I 2 Cl 4 Br 2 is proposed to have ac lassical structure with four-coordinate Ia toms bridged by two Cl atoms.…”

Polyhalogen and Polyinterhalogen Anions from Fluorine to Iodine

“…One publication deals with binary iodine-chlorine octahalides of the series [I n Cl 8Àn ] 2À (n = 3, 3.6, 4), namely [I 3 Cl 5 ] 2À ,[ I 3.6 Cl 4.4 ] 2À ,a sw ell as [I 4 Cl 4 ] 2À . [206] Similarly,t he octahalides of the series [I n Br 8Àn ] 2À (n = 0, 2, 3, 4), namely [Br 8 ] 2À ,[I 2 Br 6 ] 2À ,[I 3 Br 5 ] 2À ,and [I 4 Br 4 ] 2À ,were investigated. [207] Lastly,five mixed iodine-bromine-chlorine octahalides were characterized: [208]…”