Properties of New Asymmetrically Quaternized Dicationic Ammonium Based Room-Temperature Ionic Liquids with Ether Functionality

Eleven asymmetrically quaternized dicationic ammonium-based room-temperature ionic liquids (DRTILs) with bis­(trifluoromethanesulfonyl)­imide (TFSI) were synthesized and characterized, along with 11 analogous dibromide precursors. Two-step synthesis was used to diquaternize tetramethyl-1,3-propanediamine and 2-(dimethylamino)-ethyl ether amines with a variety of alkyl and ether functionalized side chain groups (R₁ ≠ R₂). Each salt contain 1 to 3 ether groups located either in a linkage or in a side chain moieties. Structural and thermoanalytical properties, water content, and viscosity have been characterized using, for example, NMR, mass spectrometry (MS), X-ray diffraction, and thermal analysis (TG/DTA, DSC). DRTILs have extensive fluid ranges [(∼330 to 370) °C], which are the consequence of low glass transition [(−60 to −40) °C] and high thermal degradation temperatures of the salts [(279 to 325) °C; heating rate 1.25 °C·min^–1]. Thermal stabilities of DRTILs were examined as a function of a heating rate [(1.25, 2.5, 5, 10, and 20) °C·min^–1], and degradation onset temperature overshoots of about (45 to 55) °C were observed between the slowest and the fastest heating rates. Thereby it is suggested that ILs should preferably be analyzed by TG using heating rates of ≤ 5 °C·min^–1 in order to reduce the possibility of an erroneous interpretation of the thermal stability. The ether group count and its location affected the viscosities significantly, which varied between (1150 and 6670) mPa·s at RT and lowered significantly when heated at 60 °C, being typically ≤ 200 mPa·s. The ether-functionalized DILs are potentially applicable in various IL applications, such as lubricants, heat transfer fluids, high temperature synthesis solvents, or as stationary phase in applications such as gas chromatography, MS, and capillary electrophoresis

Se-77 NMR spectroscopic, DFT MO, and VBT investigations of the reversible dissociation of solid (Se6I2)[AsF6](2)center dot 2SO(2) in liquid SO2 to solutions containing 1,4-Se6I22+ in equilibrium with Se-n(2+) (n=4, 8, 10) and seven binary selenium iodine cations: preliminary evidence for 1,1,4,4-Se4Br42+ and cyclo-Se7Br+

The composition of a complex equilibrium mixture formed upon dissolution of (Se6I2)[AsF6](2)center dot 2SO(2) in SO2(l) was studied by Se-77 NMR spectroscopy at -70 degrees C with both natural-abundance and enriched Se-77-isotope samples (enrichment 92%). Both the natural-abundance and enriched NMR spectra showed the presence of previously known cations 1,4-Se6I22+, SeI3+, 1,1,4,4-Se4I42+ Se-10(2+), Se-8(2+), and Se-4(2+). The structure and bonding in 1,4-Se6I22+ and 1,1,4,4-Se4I42+ were explored using DFT calculations. It was shown that the observed Se-Se bond alternation and presence of thermodynamically stable 4p pi-4p pi Se-Se and 4p pi-5p pi Se-I bonds arise from positive charge delocalization from the formally positively charged tricoordinate Se+. The Se-77 chemical shifts for cations were calculated using the relativistic zeroth-order regular approximation (ZORA). In addition, calculations adding a small number of explicit solvent molecules and an implicit conductor-like screening model were conducted to include the effect that solvent has on the chemical shifts. The calculations yielded reasonable agreement with experimental chemical shifts, and inclusion of solvent effects was shown to improve the agreement over vacuum values. The Se-77 NMR spectrum of the equilibrium solution showed 22 additional resonances. These were assigned on the basis of Se-77-Se-77 correlation spectroscopy, selective irradiation experiments, and spectral simulation. By combining this information with the trends in the chemical shifts, with iodine, selenium, and charge balances, as well as with ZORA chemical shift predictions, these resonances were assigned to acyclic 1,1,2-Se2I3+, 1,1,6,6-Se6I42+, and 1,1,6-Se6I3+, as well as to cyclic Se7I+ and (4-Se7I)(2)I3+. A preliminary natural-abundance Se-77 NMR study of the soluble products of the reaction of (Se-4)[AsF6](2) and bromine in liquid SO2 included resonances attributable to 1,1,4,4-Se4Br42+. These assignments are supported by the agreement of the observed and calculated 77Se chemical shifts. Resonances attributable to cyclic Se7Br+ were also observed. The thermal stability of (Se6I2)[AsF6](2)center dot 2SO(2)(S) was consistent with estimates of thermodynamic values obtained using volume-based thermodynamics (VBT) and the first application of the thermodynamic solvate difference rule for nonaqueous solvates. (Se6I2)[AsF6](2)center dot 2SO(2)(s) is the first example of a SO2 solvate for which the nonsolvated parent salt, (Se6I2)[AsF6](2)(s), is not thermodynamically stable, disproportionating to Se4I4(AsF6)(2)(s) and Se-8(AsF6)(2)(S) (Delta G degrees for the disproportion reaction is estimated to be -17 +/- 15 kJ mol(-1) at 298 K from VBT theory)