From Square‐Planar [ICl₄]⁻ to Novel Chloroiodates(III)? A Systematic Experimental and Theoretical Investigation of Their Ionic Liquids

Abstract

A systematic investigation on the existence of chloroiodates formed by reaction of Cl with I Cl , apart from the well-known [ICl ] , namely [I Cl ] and [I Cl ] , was undertaken by employing theoretical as well as experimental methods. The thermodynamic stability in terms of the complexation enthalpies and Gibbs energies, and also the decomposition of the iodine(III) polyinterhalogen anions through dichlorine elimination to form iodine (I) compounds, was studied by means of DFT and ab initio quantum-chemical calculations up to an extrapolated CCSD(T)/A'QZ level. On the experimental side, mixtures of [HMIM]Cl ([HMIM] =1-hexyl-3-methylimidazolium), [BMP]Cl ([BMP] =1-butyl-1-methylpyrrolidinium chloride) and [NEt ]Cl with 0.5, 1.0, and 1.5 equivalents of I Cl were investigated by single-crystal XRD, ion chromatography, NMR- and Raman spectroscopy. The reactions with 0.5 equivalents of I Cl resulted in the compounds [HMIM][ICl ], [BMP][ICl ], and [NEt ][ICl ], of which crystal structures were determined. The mixtures with 1.0 or 1.5 equivalents of I Cl yielded dark red liquids or suspensions of a dark red liquid with an orange solid, respectively. Both mixtures were studied by NMR-spectroscopy for the organic cation part and ion chromatography and Raman spectroscopy for the polyinterhalogen anions. The discussion of the experimental Raman spectra is supplemented with computed spectra based on the structures obtained from RI-MP2/def2-TZVPP structure optimisations. Overall [I Cl ] appears to be the predominating anionic species in mixtures with 1.0 equivalents I Cl , while mixtures with 1.5 equivalents of I Cl are suspensions of I Cl in a liquid phase containing mixed anionic interhalogen complexes.

Polyhalogen and Polyinterhalogen Anions from Fluorine to Iodine

“…However, Krossing et al. investigated mixtures of [HMIM]Cl, [BMP]Cl, or [NEt 4 ]Cl with different amounts of I 2 Cl 6 . The recorded Raman spectra of [BMP]Cl and [NEt 4 ]Cl with 1.0 equiv of I 2 Cl 6 are in agreement with quantum‐chemical calculations at the RI‐MP2/def2‐TZVPP level of theory and support the assignment of [I 2 Cl 7 ] − .…”

“…[Br 2 F 7 ] À was first described in 1976 by Sukhoverkhov et al, [184] who studied the BrF 3 /CsF/HF ternary system and reported the IR spectrum of the CsBr 2 F 7 phase.T he solid-state structure of CsBr 2 F 7 was reported in 2013 by Kraus et al [128] Thecentral fluorine atom bridges the two bromine atoms of the BrF 3 molecules and almost forms as quare-pyramidal structure.H owever,i nc ontrast to previous Raman spectroscopic investigations of Stein et al, [185] the structure neither shows aplanar anion, nor alinear Br-mF-Br unit. Stein et al also reported the Raman and IR spectra of MBr 3 F 10 (M = Cs,R b), which were both crystallized in 2016 by Kraus et al, [186] [129] Ther ecorded Raman spectra of [BMP]Cl and [NEt 4 ]Cl with 1.0 equiv of I 2 Cl 6 are in agreement with quantum-chemical calculations at the RI-MP2/def2-TZVPP level of theory and support the assignment of [I 2 Cl 7 ] À . Currently,n oc lear evidence for the formation of an [I 3 Cl 10 ] À anion has been obtained.…”

“…[124] Many of these types of anions are experimentally known and well characterized, as summarized in reviews [125] and shown in reports on higher classical interhalides. [21,124,126,[127][128][129] In nonclassical polyinterhalides,t he central halide is more electronegative than the coordinating dihalogen or interhalogen molecules ( Figure 31). [23] Thef ollowing Section focuses on non-classical polyinterhalogen anions,s tarting with compounds that are formed from either ac entral halide (X À )o rt hree-atom interhalides that are,i ne ach case,c oordinated to dihalogen molecules (Y 2 ).…”

“…Currently,n oc lear evidence for the formation of an [I 3 Cl 10 ] À anion has been obtained. [129] Polyinterhalogen dianions: To better describe the bonding situation within polyinterhalogen dianions,t he definition of non-classical polyinterhalides must be expanded. Dianions exist of several halides or interhalides,c oordinated by the same dihalogen or interhalogen.…”

Polyhalogen‐ und Polyinterhalogen‐Anionen von Fluor bis Iod

“…Die Raman‐Spektren von [BMP]Cl und [NEt 4 ]Cl mit einem Äquivalent I 2 Cl 6 stimmen gut mit quantenchemischen Rechnungen auf RI‐MP2/def2‐TZVPP‐Niveau überein und stützen die Zuordnung von [I 2 Cl 7 ] − . Ein klarer Beweis für die Existenz eines [I 3 Cl 10 ] − ‐Anions liegt gegenwärtig nicht vor …”