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

A systematic investigation on the existence of chloroiodates formed by reaction of Cl-with I2Cl6, apart from the well-known [ICl4](-), namely [I2Cl7]-and [I3Cl10](-), 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 [NEt4] Cl with 0.5, 1.0, and 1.5 equivalents of I2Cl6 were investigated by single-crystal XRD, ion chromatography, NMR-and Raman spectroscopy. The reactions with 0.5 equivalents of I2Cl6 resulted in the compounds [HMIM][ICl4], [BMP][ICl4], and [NEt4] [ICl4], of which crystal structures were determined. The mixtures with 1.0 or 1.5 equivalents of I2Cl6 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 [I2Cl7](-) appears to be the predominating anionic species in mixtures with 1.0 equivalents I2Cl6, while mixtures with 1.5 equivalents of I2Cl6 are suspensions of I2Cl6 in a liquid phase containing mixed anionic interhalogen complexes.