Weakly coordinating borate or aluminate anions have recently been shown to yield interesting properties of the resulting ionic liquids (ILs). The same is true for large phenyl-substituted imidazolium cations, which can be tuned by the choice, position, or number of substituents on the aromatic ring. We were therefore interested to combine these aryl alkyl imidazolium cations with the weakly coordinating tetrakis((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)borate [B(hfip)₄]⁻ anions to study the physical properties and viscosities of these ionic liquids. Despite the large size and high molecular weight of these readily available ILs, they are liquid at room temperature and show remarkably low glass transition points and relatively high decomposition temperatures.

The perfluorohexane-soluble and donor-free silver compound Ag(A) (A=Al(OR^F)₄; R^F=C(CF₃)₃) prepared using a facile novel route has unprecedented capabilities to form unusual and weakly bound complexes. Here, we report on the three dihalogen–silver complexes Ag(Cl₂)A, Ag(Br₂)A, and Ag(I₂)A derived from the soluble silver compound Ag(A) (characterized by single-crystal/powder XRD, Raman spectra, and quantum-mechanical calculations).

The synergistic Ag⁺/X₂ system (X=Cl, Br, I) is a very strong, but ill-defined oxidant—more powerful than X₂ or Ag⁺ alone. Intermediates for its action may include [Ag_m(X₂)_n]^m+ complexes. Here, we report on an unexpectedly variable coordination chemistry of diiodine towards this direction: (A)Ag-I₂-Ag(A), [Ag₂(I₂)₄]²⁺(A⁻)₂ and [Ag₂(I₂)₆]²⁺(A⁻)₂⋅(I₂)_x≈0.65 form by reaction of Ag(A) (A=Al(OR^F)₄; R^F=C(CF₃)₃) with diiodine (single crystal/powder XRD, Raman spectra and quantum-mechanical calculations). The molecular (A)Ag-I₂-Ag(A) is ideally set up to act as a 2 e⁻ oxidant with stoichiometric formation of 2 AgI and 2 A⁻. Preliminary reactivity tests proved this (A)Ag-I₂-Ag(A) starting material to oxidize n-C₅H₁₂, C₃H₈, CH₂Cl₂, P₄ or S₈ at room temperature. A rough estimate of its electron affinity places it amongst very strong oxidizers like MF₆ (M=4d metals). This suggests that (A)Ag-I₂-Ag(A) will serve as an easily in bulk accessible, well-defined, and very potent oxidant with multiple applications.

The synthesis and characterization of Li[O₂P{OCH(CF₃)₂}₂] (1) was investigated together with a new synthesis for Li[O₂P(OCH₂CF₃)₂] (2). The electrochemical properties of both lithium bis(fluoroalkyl)phosphates were investigated. Compound 2 was prepared by deprotonation of the conjugate acid HO(O)P(OCH₂CF₃)₂ (3), of which the crystal structure was solved. Lithium bis(fluoroalkyl)phosphates 1 and 2 were used to prepare gel electrolytes on the basis of a coordination network held together solely by ionic interactions between the lithium ions and the anions. The preparation of the gel electrolytes produced with 2 and their properties were explored.

The synergistic Ag⁺/X₂ system (X=Cl, Br, I) is a very strong, but ill-defined oxidant—more powerful than X₂ or Ag⁺ alone. Intermediates for its action may include [Ag_m(X₂)_n]^m+ complexes. Here, we report on an unexpectedly variable coordination chemistry of diiodine towards this direction: (A)Ag-I₂-Ag(A), [Ag₂(I₂)₄]²⁺(A⁻)₂ and [Ag₂(I₂)₆]²⁺(A⁻)₂⋅(I₂)_x≈0.65 form by reaction of Ag(A) (A=Al(OR^F)₄; R^F=C(CF₃)₃) with diiodine (single crystal/powder XRD, Raman spectra and quantum-mechanical calculations). The molecular (A)Ag-I₂-Ag(A) is ideally set up to act as a 2 e⁻ oxidant with stoichiometric formation of 2 AgI and 2 A⁻. Preliminary reactivity tests proved this (A)Ag-I₂-Ag(A) starting material to oxidize n-C₅H₁₂, C₃H₈, CH₂Cl₂, P₄ or S₈ at room temperature. A rough estimate of its electron affinity places it amongst very strong oxidizers like MF₆ (M=4d metals). This suggests that (A)Ag-I₂-Ag(A) will serve as an easily in bulk accessible, well-defined, and very potent oxidant with multiple applications.

The perfluorohexane-soluble and donor-free silver compound Ag(A) (A=Al(OR^F)₄; R^F=C(CF₃)₃) prepared using a facile novel route has unprecedented capabilities to form unusual and weakly bound complexes. Here, we report on the three dihalogen–silver complexes Ag(Cl₂)A, Ag(Br₂)A, and Ag(I₂)A derived from the soluble silver compound Ag(A) (characterized by single-crystal/powder XRD, Raman spectra, and quantum-mechanical calculations).

Lithium chloro- and bromoaluminates were prepared, fully characterized, and investigated as conducting salts for battery applications. In addition, thermodynamic investigations of their lattice enthalpies and other quantities were carried out. The Li[AlX₄] salts also show very high conductivities in solvents of very low polarity, which makes them suitable candidates for conducting salts and battery systems working with voltages below ca. 3.5 V (X = Br) or ca. 4.4 V (X = Cl), such as lithium-sulfur batteries (LSBs). In particular, the bromoaluminates, with their Pearson-soft character, which prevents ion-pair formation with the Pearson-hard lithium ion, are promising for this purpose. An interesting alternative solvent for LSBs might be o-difluorobenzene, in which Li[AlBr₄] shows very high solubility and conductivity. The carbonate solvents typically used for LIBs are not suitable for the bromoaluminates, and Li[AlCl₄] also shows corrosive behavior towards aluminum at potentials higher than 2.5 V. This can be prevented by, for example, addition of Li[PF₆].

Using [Ga(C₆H₅F)₂]⁺[Al(OR^F)₄]⁻(1) (R^F=C(CF₃)₃) as starting material, we isolated bis- and tris-η⁶-coordinated gallium(I) arene complex salts of p-xylene (1,4-Me₂C₆H₄), hexamethylbenzene (C₆Me₆), diphenylethane (PhC₂H₄Ph), and m-terphenyl (1,3-Ph₂C₆H₄): [Ga(1,4-Me₂C₆H₄)_2.5]⁺ (2⁺), [Ga(C₆Me₆)₂]⁺ (3⁺), [Ga(PhC₂H₄Ph)]⁺ (4⁺) and [(C₆H₅F)Ga(μ-1,3-Ph₂C₆H₄)₂Ga(C₆H₅F)]²⁺ (5²⁺). 4⁺ is the first structurally characterized ansa-like bent sandwich chelate of univalent gallium and 5²⁺ the first binuclear gallium(I) complex without a GaGa bond. Beyond confirming the structural findings by multinuclear NMR spectroscopic investigations and density functional calculations (RI-BP86/SV(P) level), [Ga(PhC₂H₄Ph)]⁺[Al(OR^F)₄]⁻(4) and [(C₆H₅F)Ga(μ-1,3-Ph₂C₆H₄)₂Ga(C₆H₅F)]²⁺{[Al(OR^F)₄] ⁻}₂ (5), featuring ansa-arene ligands, were tested as catalysts for the synthesis of highly reactive polyisobutylene (HR-PIB). In comparison to the recently published 1 and the [Ga(1,3,5-Me₃C₆H₃)₂]⁺[Al(OR^F)₄]⁻ salt (6) (1,3,5-Me₃C₆H₃=mesitylene), 4 and 5 gave slightly reduced reactivities. This allowed for favorably increased polymerization temperatures of up to +15 °C, while yielding HR-PIB with high contents of terminal olefinic double bonds (α-contents=84–93 %), low molecular weights (M_n=1000–3000 g mol⁻¹) and good monomer conversions (up to 83 % in two hours). While the chelate complexes delivered more favorable results than 1 and 6, the reaction kinetics resembled and thus concurred with the recently proposed coordinative polymerization mechanism.

The straightforward synthesis of the cationic, purely organometallic Ni^I salt [Ni(cod)₂]⁺[Al(OR^F)₄]⁻ was realized through a reaction between [Ni(cod)₂] and Ag[Al(OR^F)₄] (cod=1,5-cyclooctadiene). Crystal-structure analysis and EPR, XANES, and cyclic voltammetry studies confirmed the presence of a homoleptic Ni^I olefin complex. Weak interactions between the metal center, the ligands, and the anion provide a good starting material for further cationic Ni^I complexes.

Bulk protonated mesitylene, toluene, and benzene bromoaluminate salts were stabilized and characterized in the superacidic system HBr/n AlBr₃ with NMR spectroscopy and X-ray analysis of [HC₆H₃(CH₃)₃]⁺[AlBr₄]⁻ (1), [HC₆H₅(CH₃)]⁺[AlBr₄]⁻ (2), and [C₆H₇]⁺[Al₂Br₇]⁻⋅C₆H₆ (3). Protonation attempts in bromoaluminate ILs led to a complete protonation of mesitylene, and a protonation degree of up to 15 % for toluene in the IL BMP⁺[Al₂Br₇]⁻. Benzene could only be protonated in the more acidic IL BMP⁺[Al₃Br₁₀]⁻, with a degree of 25 %. Protonation attempts on aromatics provide evidence that the bromoaluminate ILs tolerate superacidic environments. On the basis of the absolute Brønsted acidity scale, quantum chemical calculations confirmed the superacidic properties, and rank the acidities in ILs down to a pH_abs value of 164 with an error of less than one pH unit compared with experimental findings. The neat AlBr₃/HBr system even may reach acidities down to pH_abs 163.

A new Li salt with views to success in electrolytes is synthesized in excellent yields from lithium borohydride with excess 2,2,2-trifluorethanol (HOTfe) in toluene and at least two equivalents of 1,2-dimethoxyethane (DME). The salt Li[B(OTfe)₄] is obtained in multigram scale without impurities, as long as DME is present during the reaction. It is characterized by heteronuclear magnetic resonance and vibrational spectroscopy (IR and Raman), has high thermal stability (T_{decomposition}>271 °C, DSC) and shows long-term stability in water. The concentration-dependent electrical conductivity of Li[B(OTfe)₄] is measured in water, acetone, EC/DMC, EC/DMC/DME, ethyl acetate and THF at RT In DME (0.8 mol L⁻¹) it is 3.9 mS cm⁻¹, which is satisfactory for the use in lithium-sulfur batteries (LiSB). Cyclic voltammetry confirms the electrochemical stability of Li[B(OTfe)₄] in a potential range of 0 to 4.8 V vs. Li/Li⁺. The performance of Li[B(OTfe)₄] as conducting salt in a 0.2 mol L⁻¹ solution in 1:1 wt % DME/DOL is investigated in LiSB test cells. After the 40th cycle, 86 % of the capacity remains, with a coulombic efficiency of around 97 % for each cycle. This indicates a considerable performance improvement for LiSB, if compared to the standard Li[NTf₂]/DOL/DME electrolyte system.

Although receiving large interest over the last years, some fundamental aspects of Brønsted acidity in ionic liquids (ILs) have up to now been insufficiently highlighted. In this work, standard states, activity, and activity coefficient definitions for IL solvent systems were developed from general thermodynamic considerations and then extended to a general mixed solvent standard state. By using the bromide/bromoaluminate systems as representative ILs, formulae for thermodynamically consistent pH scales for ILs with simple (Br⁻) and complex ([Al_nBr_3n+1]⁻) anions were derived on the basis of the chemical potential of the proton. Supported by quantum chemical [ccsd(t)/MP2/DFT/COSMO-RS] calculations, Gibbs solvation energies of the proton were calculated, which allowed the ILs to be ranked in absolute acidity, that is, pH_abs or μ_abs(H⁺, IL), and additionally allowed their acidity to be compared with molecular Brønsted acid systems. It was shown that bromoaluminate ILs are suited for reaching superacidic conditions. The complexity of autoprotolysis processes in C₆MIM⁺[AlBr₄]⁻ (C₆MIM=1-hexyl-3-methylimidazolium) with or without the addition of basic (i.e. Br⁻) or acidic (AlBr₃ and/or HBr) solutes was examined in detail by model calculations, and they indicated a large thermodynamic influence of small deviations from the exact stoichiometric composition.

Several ionic liquids (ILs) comprising [B(hfip)₄]⁻ [hfip=OCH(CF₃)₂] or [Al(hfip)₄]⁻ anions and imidazolium or ammonium cations were prepared and mixed with up to 270 mol % of dimethyl carbonate (DMC). The viscosities, conductivities, and self-diffusion constants of these mixtures and, where possible, of the neat ILs were measured and compared with common [NTf₂]⁻ based ILs and their mixtures with DMC. A tremendous decrease of the viscosities and a likewise increase of the conductivities and diffusion constants can be achieved for all classes of ILs. However, the order of the conductivities is partially reversed in the diffusion data. This is probably due to the low dielectric constant of DMC and the, thus, favored ion pairing, as evidenced, for example, by the calculated ionicities. Altogether, our data show that the chemically robust, but high-melting and more viscous [B(hfip)₄]⁻ ILs might be candidates for electrolytes when mixed with suitable molecular solvents.

The straightforward synthesis of the cationic, purely organometallic Ni^I salt [Ni(cod)₂]⁺[Al(OR^F)₄]⁻ was realized through a reaction between [Ni(cod)₂] and Ag[Al(OR^F)₄] (cod=1,5-cyclooctadiene). Crystal-structure analysis and EPR, XANES, and cyclic voltammetry studies confirmed the presence of a homoleptic Ni^I olefin complex. Weak interactions between the metal center, the ligands, and the anion provide a good starting material for further cationic Ni^I complexes.

To answer the question as to whether gallium in its oxidation state +1 favors a σ- or a π-coordination of aromatic nitrogen bases, we reacted [Ga(C₆H₅F)₂]⁺[Al(OR^F)₄]^– {R^F = C(CF₃)} with pyrazine and 2,6-di-tert-butyl-4-methylpyridine (DTBMP). In doing so, we obtained the first tricoordinate, nonchelated, homoleptic N-donor complex of gallium(I): [Ga(pyrazine)₃]⁺[Al(OR^F)₄]^–, in which each gallium(I) cation is coordinated in a trigonal-pyramidal fashion by three η¹-donating pyrazine ligands. Hence, the gallium(I) cations favor σ- over π-coordination. Depending on the reaction conditions, and due to the bifunctionality of pyrazine, 1D coordination polymers of {[Ga(μ-pyrazine)₂(η¹-pyrazine)]⁺[Al(OR^F)₄]^–}_∞ were also obtained. With the sterically demanding DTBMP, which is conventionally used as a proton scavenger, the mixed complex [Ga(C₆H₅F)₂(DTBMP)]⁺[Al(OR^F)₄]^– was isolated, thus proving incorrect the perception of DTBMP being “non-nucleophilic”. The structural findings were confirmed by multinuclear NMR investigations and density functional performed at the RI-BP86/SV(P) level.

Density functional theory (DFT) calculations for the six-membered ring 1,4-(CH₂)₂(P^tBu)₄ (1), the dimer (P^tBu₂)₂ (2) and the 2,5-chalcogenated derivatives of 1, 3a (E = S) and 3b (E = Se), and the corresponding cation radicals and dications predict significant structural changes upon oxidation. The formation of a transannular P–P single bond (ca. 2.25 Å) in the three cyclic dications 1²⁺, 3a²⁺, and 3b²⁺ is indicated by geometry and consideration of the frontier orbitals. The calculations also indicate a weak transannular interaction in the cyclic cation radicals. The nature of these transannular P–P bonding interactions is analyzed through a consideration of the molecular orbitals involved. Cyclic Voltammetry studies of 1 and 2 reveal two well-separated oxidation processes. Both processes are irreversible for 1 at normal scan rates, whereas for 2 the first process is quasi-reversible. The cation radical 1^+• could not be detected by in situ electron paramagnetic resonance studies of the first electrochemical oxidation, but a spectrum for the radical cation 2^+• could be observed. The difference in the redox behavior of 1 and 2 is considered with respect to the structural parameters and DFT calculations. Chemical oxidation of 1 with NO⁺[Al(OR^F)₄]⁻ (R^F = C(CF₃)₃) in CH₂Cl₂ led to a complex mixture; the protonated cation H1⁺ (1,4-(CH₂)₂(P^tBu)₃(HP^tBu)⁺) was identified as one of the major products on the basis of multinuclear NMR spectra.

The molecular interaction potentials, including S (dipolarity/polarizability), A (hydrogen bonding acidity), and B (hydrogen bonding basicity), of anions are experimentally determined using multi-functionalized stationary phases in high-performance liquid chromatography (HPLC) systems. We employ three different multi-functionalized stationary phase columns (Obelisc R, Obelisc N, and Acclaim Trinity-P1) combined with two ingredients, namely, acetonitrile (ACN) and methanol (MeOH). These conditions can cause neutral, cationic, and anionic compounds to be retained. By using the retention characteristics of calibration compounds, including cations, anions, and neutral compounds, system parameters including the ionic interaction terms (z_cZ_c, z_aZ_a) are evaluated using multiple linear regression, resulting in a standard deviation (SD) of 0.090–0.158 log units. Based on the system parameters and retention characteristics of the anions of interest, their molecular interaction potentials are characterized on the same scale for neutral and cationic molecules. Furthermore, to verify the determined molecular interaction potentials, we predict anion hydrophobicity. The results show that the determined S, A, and B, together with the computable descriptors E (excess molar refraction) and V (McGowan volume), can predict anion hydrophobicity with R²=0.982 and SD=0.167 (dimensionless).

Upon reaction of gaseous Me₃SiF with the in situ prepared Lewis acid Al(OR^F)₃, the stable ion-like silylium compound Me₃Si-F-Al(OR^F)₃ 1 forms. The Janus-headed 1 is a readily available smart Lewis acid that differentiates between hard and soft nucleophiles, but also polymerizes isobutene effectively. Thus, in reactions of 1 with soft nucleophiles (Nu), such as phosphanes, the silylium side interacts in an orbital-controlled manner, with formation of [Me₃SiNu]⁺ and the weakly coordinating [FAl(OR^F)₃]^– or [(^FRO)₃Al-F-Al(OR^F)₃]^– anions. If exchanged for hard nucleophiles, such as primary alcohols, the aluminum side reacts in a charge-controlled manner, with release of FSiMe₃ gas and formation of the adduct R(H)OAl(OR^F)₃. Compound 1 very effectively initiates polymerization of 8 to 21 mL of liquid C₄H₈ in 50 mL of CH₂Cl₂ already at temperatures between −57 and −30 °C with initiator loads as low as 10 mg in a few seconds with 100 % yield but broad polydispersities.

The easily accessible hexafluoroisopropoxysulfuric acid (1, hfipOSO₃H; hfip=C(H)(CF₃)₂) was synthesized by the reaction of hexafluoroisopropanol and chlorosulfonic acid on the kilogram scale and isolated in 98 % yield. The calculated gas-phase acidity (GA) value of 1 is 58 kJ mol⁻¹ lower in ΔG° than that of sulfuric acid (GA value determined by a CCSD(T)-MP2 compound method). Considering the gas-phase dissociation constant as a measure for the intrinsic molecular acid strength, a hfipOSO₃H molecule is more than ten orders of magnitude more acidic than a H₂SO₄ molecule. The acid is a liquid at room temperature, distillable at reduced pressure, stable for more than one year in a closed vessel, reactive towards common solvents, and decomposes above 180 °C. It is a versatile compound for further applications, such as the synthesis of ammonium- and imidazolium-based air- and moisture-stable protic ionic liquids (pILs). Among the six synthesized ionic compounds, five are pILs with melting points below 100 °C and three of them are liquids at nearly room temperature. The conductivities and viscosities of two representative ILs were investigated in terms of Walden plots, and the pILs were found to be little associated ILs, comparable to conventional aprotic ILs.

Crystalline and properly ordered protonated benzene as the [C₆H₇]⁺[Al₂Br₇]⁻⋅(C₆H₆) salt 1 are obtained by the combination of solid AlBr₃, benzene, and HBr gas. Compound 1 was characterized and verified by NMR, Raman and X-Ray spectroscopy. This unexpected simple and straight forward access shows that HBr/AlBr₃ is an underestimated superacid that should be used more frequently.

The charge scaling effect in ionic liquids was explored on the basis of experimental and theoretical charge-density analyses of [C₁MIM][C₁SO₄] employing the quantum theory of atoms in molecules (QTAIM) approach. Integrated QTAIM charges of the experimental (calculated) charge density of the cation and anion resulted in non-integer values of ±0.90 (±0.87) e. Efficient charge transfer along the bond paths of the hydrogen bonds between the imidazolium ring and the anion was considered as the origin of these reduced charges. In addition, a detailed QTAIM analysis of the bonding situation in the [C₁SO₄]⁻ anion revealed the presence of negative π_Oσ*_S-O hyperconjugation.

Die Reaktion von festem AlBr₃, Benzol und HBr-Gas führte zur ausgeordneten Kristallstruktur des protonierten Benzols der Zusammensetzung [C₆H₇]⁺[Al₂Br₇]⁻⋅(C₆H₆) (1). Die Verbindung konnte mittels Röntgenstrukturanalyse, NMR- und Raman-Spektroskopie zweifelsfrei nachgewiesen werden. Dieser unerwartet einfache und leicht zugängliche Syntheseweg zeigt, dass HBr/AlBr₃ eine Supersäure ist, deren Potential bisher unterschätzt wurde und noch weiter untersucht werden sollte.

The easily accessible hexafluoroisopropoxysulfuric acid (1, hfipOSO₃H; hfip=C(H)(CF₃)₂) was synthesized by the reaction of hexafluoroisopropanol and chlorosulfonic acid on the kilogram scale and isolated in 98 % yield. The calculated gas-phase acidity (GA) value of 1 is 58 kJ mol⁻¹ lower in ΔG° than that of sulfuric acid (GA value determined by a CCSD(T)-MP2 compound method). Considering the gas-phase dissociation constant as a measure for the intrinsic molecular acid strength, a hfipOSO₃H molecule is more than ten orders of magnitude more acidic than a H₂SO₄ molecule. The acid is a liquid at room temperature, distillable at reduced pressure, stable for more than one year in a closed vessel, reactive towards common solvents, and decomposes above 180 °C. It is a versatile compound for further applications, such as the synthesis of ammonium- and imidazolium-based air- and moisture-stable protic ionic liquids (pILs). Among the six synthesized ionic compounds, five are pILs with melting points below 100 °C and three of them are liquids at nearly room temperature. The conductivities and viscosities of two representative ILs were investigated in terms of Walden plots, and the pILs were found to be little associated ILs, comparable to conventional aprotic ILs.

For heterogeneous catalysts, the constitution of the precursor is an important parameter to adjust the properties of the active catalyst. Therefore, we examined the influence of the temperature during the precipitation process and during the ageing time in the mother liquor for a Cu/ZnO/ZrO₂ catalyst system obtained through a coprecipitation route. The variation of the temperature affects the ratio and crystallinity of the precursor phases zincian malachite and aurichalcite, as detected by powder XRD (phase and line width) and FTIR spectroscopy (characteristic asymmetric CO stretching modes of the carbonate anions at =1600–1100 cm⁻¹). Therefore, the precatalyst surface area (A_s,BET) and pore distribution are adjustable (i.e., A_s,BET of 190 m² g⁻¹ was reached). The influence of the synthesis conditions on the catalysts activity for methanol production was analyzed and discussed up to the level of productivity/activity testing at 413/513 K and 40 bar total H₂/CO₂ pressure. The best catalyst showed a methanol productivity of 9.16 mmol g_cat⁻¹ h⁻¹ (513 K, 40 bar, and gas hourly space velocity=8000) and is better than an industrial catalyst tested under the same conditions (8.34 mmol g_cat⁻¹ h⁻¹). However, despite considerable differences in the precursor and precatalyst structure and morphology, their influence on the methanol productivity is only small. This demonstrates that the active catalyst is formed under reaction conditions.

The room-temperature ionic liquid (RT-IL) [C(CH₃)₃]⁺ [Al₂Br₇]⁻ (m.p. 2 °C) was generated by bromide abstraction from tert-butyl bromide with the Lewis acid aluminum bromide in the absence of solvent. The crystal structure of the tert-butyl cation salt was determined by X-ray diffraction. NMR, IR, and Raman spectroscopy, as well as quantum-chemical and thermodynamic calculations, confirm the composition of this RT-IL. Thus, one may consider this RT-IL to be a readily accessible (and on a large scale) cationic Brønsted acid (protonated isobutene) with the potential for further reactivity. Based on the new absolute Brønsted acidity scale, we calculated an absolute pH_abs value of 171 for liquid bulk [C(CH₃)₃]⁺ [Al₂Br₇]⁻. This value is about as acidic as 100 % sulfuric acid (pH_abs=171) and, thus, on the edge of superacidity.

A novel minireactor for direct fluorination of organic and inorganic substances was tested. The reactor consists of nickel-coated copper blocks with mechanically machined 1 mm channels and is equipped with an active cooling system. The direct fluorination of ethylene carbonate and propylene carbonate is described. For the fluorinated propylene carbonate, the NMR data of various fluorinated isomers were determined. The Gibbs reaction energies for the direct fluorination of ethylene and propylene carbonate were calculated at the reliable G3 level of theory. The excellent decomposition stability of the cyclic carbonates against high fluorine and HF concentrations also qualifies them as good solvents for direct fluorination processes, especially for ionic substrates. In this respect, the direct fluorination of the inorganic salt closo-K₂[B₁₂H₁₂] in cyclic carbonates is presented.

Invited for this month’s cover are the groups of Prof. Ingo Krossing and Prof. Peter Woias based at Albert-Ludwigs-Universität Freiburg as well as Prof. Carsten Knapp who is now at Bergische Universität Wuppertal. The background of the cover picture shows the Rhine Falls (Schaffhausen, Switzerland), which is the largest waterfall in Europe and only one hour away from the laboratories in Freiburg. The waterfall symbolizes flow chemistry and the wild nature of direct fluorination reactions.

In order to understand molecular interaction potentials of 30 cations of ionic liquids (ILs), the well-known linear free energy relationship concept (LFER) was applied. The LFER descriptors for the excess molar refractivity and the molar volume were calculated in silico and for hydrogen-bonding acidity and basicity, and the polarizability/dipolarity of IL cations were experimentally determined through high performance liquid chromatography (HPLC) measurements. For the study, three different columns (RP-select B, Cyan, and Diol) and buffered mobile phases, based on two organic solvents acetonitrile (ACN) and methanol (MeOH), were selectively combined to the HPLC separation systems RP-select B-ACN, RP-select B-MeOH, Cyan-MeOH, Diol-ACN, and Diol-MeOH. By measuring the retention factors of 45 neutral calibration compounds and calculating LFER descriptors of three cations in the HPLC systems, the system parameters, including an ionic z coefficient, were determined. Conversely, the LFER descriptors of 30 ionic liquid cations were determined, based on the parameters of five systems and their retention factors in the HPLC systems. The results showed that the type of head group, alkyl chain length and further substituents of the cation have a significant influence on the dipolarity/polarizability and the hydrogen-bonding acidity, and functionalized groups (hydroxyl, ether, and dimethylamino) lead to hydrogen-bonding basicity of the cation. The characterization of cationic LFER descriptors opens up the chance for a more quantitative understanding of molecular interaction potentials and physicochemical properties of ILs.

Straightforward access to hydridoborate-based ionic liquids (BILs) is provided. They fall into a barely developed area of research and are of interest as, for example, reagents for organic synthesis. A series of pure [BH₄]⁻ ILs with 1-butyl-2,3-dimethylimidazolium (BMMIM), 1-ethyl-3-methylimidazolium (EMMIM), 1-propyl-1-methylpiperidinium (PropMPip), and1-butyl-1-methylpyrrolidinium (BMP) cations were prepared. All synthesized ILs are well soluble in CH₂Cl₂. We developed a procedure that gives clean products with correct elemental analyses. In contrast to earlier reports, which when conducted by us yielded only mixtures of the boranate anion with major halide contamination (maximum [BH₄]⁻ content: 77.5 %). These materials can be viewed as the starting material for the (hypothetical) hydrogen-storage redox shuttling sequence between [BH₄]⁻ and [B₁₂H₁₂]²⁻, in which the triboranate anion [B₃H₈]⁻ is a formal intermediate. Here we also developed a facile route to [B₃H₈]⁻ ILs with [BMMIM]⁺, [EMMIM]⁺, [PropMPip]⁺, and [NBu₄]⁺, in which Na[BH₄] reacts in situ (enhanced by ultrasound) with the solvent CH₂Cl₂ as the oxidizing agent to give the triboranate IL in high yield and purity according to the equation: 3 [BH₄]⁻+2 CH₂Cl₂+[Cat]⁺[B₃H₈]⁻[Cat]⁺+H₂+2 CH₃Cl+2 Cl⁻. We further investigated this reaction path by additional NMR spectroscopic experiments, powder-XRD analysis, and quantum chemical DFT calculations.

The capability of a gaseous Brønsted acid HB to deliver protons to a base is usually described by the gas-phase acidity (GA) value of the acid. However, GA values are standard Gibbs energy differences and refer to individual gas pressures of 1 bar for acid HB, base B⁻, and proton H⁺. We show that the GA value is not suited to describe the bulk acidity of a gaseous acid. Here the pressure dependence of the activities of HB, H(HB)_n⁺, and B(HB)_m⁻ that result from gaseous autoprotolysis have to be considered. In this work, the pressure-dependent absolute chemical potential of the proton in the representative gaseous proton acids CH₄, NH₃, H₂O, HF, and HCl was worked out and the general theory to describe bulk gas phase acidity—that can directly be compared with solution acidity—was developed.

Two new ionic liquids (ILs) with siloxane-functionalized cations and the weakly coordinating tetraalkoxyaluminate [Al(hfip)₄]⁻ (hfip=hexafluoroisopropoxy) are prepared and characterized by nuclear magnetic resonance (NMR), infrared (IR) and Raman spectroscopy. With melting points below 0 °C they qualify as room temperature ILs (RTILs). Their temperature-dependent viscosities and conductivities, together with those of two [Tf₂N]⁻ ILs with the same cations and a further siloxane-functionalized [Tf₂N]⁻ IL, are measured between 0 and 80 °C, and all are described by the Vogel–Fulcher–Tammann (VFT) equations. We note that the [Al(hfip)₄]⁻ ILs have lower viscosities than their [Tf₂N]⁻ analogues at all measured temperatures and higher conductivities at room temperature.

In a new oxidative route, Ag⁺[Al(OR^F)₄]⁻ (R^F=C(CF₃)₃) and metallic indium were sonicated in aromatic solvents, such as fluorobenzene (PhF), to give a precipitate of silver metal and highly soluble [In(PhF)_n]⁺ salts (n=2, 3) with the weakly coordinating [Al(OR^F)₄]⁻ anion in quantitative yield. The In⁺ salt and the known analogous Ga⁺[Al(OR^F)₄]⁻ were used to synthesize a series of homoleptic PR₃ phosphane complexes [M(PR₃)_n]⁺, that is, the weakly PPh₃-bridged [(Ph₃P)₃In–(PPh₃)–In(PPh₃)₃]²⁺ that essentially contains two independent [In(PPh₃)₃]⁺ cations or, with increasing bulk of the phosphane, the carbene-analogous [M(PtBu₃)₂]⁺ (M=Ga, In) cations. The M^IP distances are 27 to 29 pm longer for indium, and thus considerably longer than the difference between their tabulated radii (18 pm). The structure, formation, and frontier orbitals of these complexes were investigated by calculations at the BP86/SV(P), B3LYP/def2-TZVPP, MP2/def2-TZVPP, and SCS-MP2/def2-TZVPP levels.

TeX₃[Al(OR^F)₄] (X=Cl, Br, I; R^F=C(CF₃)₃) were synthesized by the reaction of Ag[Al(OR^F)₄] and TeX₄ or the reaction of AuX, Ag[Al(OR^F)₄], and elemental tellurium in liquid SO₂. The compounds were characterized by ¹²⁵Te NMR in solution and by X-ray diffraction, Raman, and IR spectroscopy in the solid state. The vibrational spectra and the crystal structure show very weak secondary interactions, indicating “pseudo gas phase conditions” in the condensed phase. The observed trend of the ¹²⁵Te NMR chemical shifts along the [TeX₃]⁺ series follows neither the monotonous decrease known as “normal halogen dependence” nor the increase known as “inverse halogen dependence”. By relativistic two-component calculations based on the ZORA approach, we find that this “abnormal halogen dependence” results from an interplay of relativistic and solvent effects, where non-negligible scalar relativistic effects and intermediate-sized spin-orbit effects compensate to some extent. The reasons for these trends are evaluated in the context of the Te s-orbital character of the TeX bonds and compared with the halogen dependence(s) within the isoelectronic [SeX₃]⁺ and PX₃ series and related trihalomethyl [CX₃]⁺ cations.

A series of bis(trifluoromethylsulfonyl)imide ionic liquids (ILs) with classical as well as mildly functionalized cations was prepared and their viscosities and conductivities were determined as a function of the temperature. Both were analyzed with respect to Arrhenius, Litovitz and Vogel–Fulcher–Tammann (VFT) behaviors, as well as in the context of their molecular volume (V_m). Their viscosity and conductivity are highly correlated with V_m/T or related expressions (R²≥0.94). With the knowledge of V_m of new cations, these correlations allow the temperature-dependent prediction of the viscosity and conductivity of hitherto unknown, non- or mildly functionalized ILs with low error bars (0.05 and 0.04 log units, respectively). The influence of the cation structure and mild functionalization on the physical properties was studied with systematically altered cations, in which V_m remained similar. The T_o parameter obtained from the VFT fits was compared to the experimental glass temperature (T_g) and the T_g/T_o ratio for each IL was calculated using both experimental values and Angell’s relationship. With Walden plots we investigated the IL ionicity and interpreted it in relation to the cation effects on the physical IL properties. We checked the validity of these V_m/T relations by also including the recently published variable temperature viscosity and conductivity data of the [Al(OR^F)₄]⁻ ILs with R^F=C(H)(CF₃)₂ (error bars for the prediction: 0.09 and 0.10 log units, respectively).

An investigation of the melting points of 520 organic 1:1 salts is presented with the aim of developing a universal, simple, physically well-founded prediction scheme. The general reliability and reproducibility of the recorded experimental data are discussed with respect to purity, phase behavior, disorder and thermal history of a given substance. Additionally, mistakes, systematic errors, or lack of conventions can lead to considerable differences in the experimental measurements. A rough error bar for the reproducibility of the melting points of organic salts of ±5 to ±15 °C can be assigned. With this restraint, we developed two simple, semiempirical, five- and nine-parameter schemes with easy-to-calculate quantities. With these, we could predict the melting temperature of a given organic salt in the temperature range of −25 to +300 °C with an average error of 33.5 °C and a relative error of 9.3 %. All calculated quantities are assessed with the help of conventional DFT, COSMO and COSMO-RS calculations, and are currently implemented into the IL-Prop module of the upcoming version of COSMOtherm. These prediction schemes are suitable for high-throughput computational screening of substances in the context of “computer-aided synthesis”. Therefore, they are valuable tools to find a compound with a suitable melting point before its first synthesis.

The COSMO cluster-continuum (CCC) solvation model is introduced for the calculation of standard Gibbs solvation energies of protons. The solvation sphere of the proton is divided into an inner proton–solvent cluster with covalent interactions and an outer solvation sphere that interacts electrostatically with the cluster. Thus, the solvation of the proton is divided into two steps that are calculated separately: 1) The interaction of the proton with one or more solvent molecules is calculated in the gas phase with high-level quantum-chemical methods (modified G3 method). 2) The Gibbs solvation energy of the proton–solvent cluster is calculated by using the conductor-like screening model (COSMO). For every solvent, the solvation of the proton in at least two (and up to 11) proton–solvent clusters was calculated. The resulting Gibbs solvation energies of the proton were weighted by using Boltzmann statistics. The model was evaluated for the calculation of Gibbs solvation energies by using experimental data of water, MeCN, and DMSO as a reference. Allowing structural relaxation of the proton–solvent clusters and the use of structurally relaxed Gibbs solvation energies improved the accordance with experimental data especially for larger clusters. This variation is denoted as the relaxed COSMO cluster-continuum (rCCC) model, for which we estimate a 1σ error bar of 10 kJ mol⁻¹. Gibbs solvation energies of protons in the following representative solvents were calculated: Water, acetonitrile, sulfur dioxide, dimethyl sulfoxide, benzene, diethyl ether, methylene chloride, 1,2-dichloroethane, sulfuric acid, fluorosulfonic acid, and hydrogen fluoride. The obtained values are absolute chemical standard potentials of the proton (pH=0 in this solvent). They are used to anchor the individual solvent specific acidity (pH) scales to our recently introduced absolute acidity scale.

The pnictocenium salts [Cp*PCl]⁺[μCl]⁻ (1 a), [Cp*PCl]⁺[ClAl(OR^F)₃]⁻ (1 b), [Cp*AsCl]⁺[ClAl(OR^F)₃]⁻ (2), and [(Cp*)₂P]⁺[μCl]⁻ (3), in which Cp*=Me₅C₅, μCl=(^FRO)₃AlClAl(OR^F)₃, and OR^F=OC(CF₃)₃, were prepared by halide abstraction from the respective halopnictines with the Lewis superacid PhFAl(OR^F)₃.1 The X-ray crystal structures of 1 a, 2, and 3 established that in the half as well as in the sandwich cations the Cp* rings are attached in an η²-fashion. By using one or two equivalents of the Lewis acid, the two new weakly coordinating anions [μCl]⁻ and [ClAl(OR^F)₃]⁻ resulted. They also stabilize the highly reactive cations in PhF or 1,2-F₂C₆H₄ solution at room temperature. The chloride ion affinities (CIAs) of a range of classical strong Lewis acids were also investigated. The calculations are based on a set of isodesmic BP86/SV(P) reactions and a non-isodesmic reference reaction assessed at the G3MP2 level.

We present the full enthalpic phase transition cycle for ionic liquids (ILs) as examples of non-classical salts. The cycle was closed for the lattice, solvation, dissociation, and vaporization enthalpies of 30 different ILs, relying on as much experimental data as was available. High-quality dissociation enthalpies were calculated at the G3 MP2 level. From the cycle, we could establish, for the first time, the lattice and solvation enthalpies of ILs with imidazolium ions. For vaporization, lattice, and dissociation enthalpies, we also developed new prediction methods in the course of our investigations. Here, as only single-ion values need to be calculated and the tedious optimization of an ion pair can be circumvented, the computational time is short. For the vaporization enthalpy, a very simple approach was found, using a surface term and the calculated enthalpic correction to the total gas-phase energy. For the lattice enthalpy, the most important constituent proved to be the calculated conductor-like screening model (COSMO) solvation enthalpy in the ideal electric conductor. A similar model was developed for the dissociation enthalpy. According to our assessment, the typical error of the lattice enthalpy would be 9.4 kJ mol⁻¹, which is less than half the deviation we get when using the (optimized) Kapustinskii equation or the recent volume-based thermodynamics (VBT) theory. In contrast, the non-optimized VBT formula gives lattice enthalpies 20 to 140 kJ mol⁻¹ lower than the ones we assessed in the cycle, because of the insufficient description of dispersive interactions. Our findings show that quantum-chemical calculations can greatly improve the VBT approaches, which were parameterized for simple, inorganic salts with ideally point-shaped charges. In conclusion, we suggest the term “augmented VBT”, or “aVBT”, to describe this kind of theoretical approach.

A large series of ionic liquids (ILs) based on the weakly coordinating alkoxyaluminate [Al(hfip)₄]⁻ (hfip: hexafluoroisopropoxy) with classical as well as functionalized cations were prepared, and their principal physical properties determined. Melting points are between 0 ([C₄MMIM][Al(hfip)₄]) and 69 °C ([C₃MPip][Al(hfip)₄]); three qualify as room-temperature ILs (RTILs). Crystal structures for six ILs were determined; their structural parameters and anion–cation contacts are compared here with known ILs, with a special focus on their influence on physical properties. Moreover, the biodegradability of the compounds was investigated by using the closed-bottle and the manometric respirometry test. Temperature-dependent viscosities and conductivities were measured between 0 and 80 °C, and described by either the Vogel–Fulcher–Tammann (VFT) or the Arrhenius equations. Moreover, conductivities and viscosities were investigated in the context of the molecular volume, V_m. Physical property–V_m correlations were carried out for various temperatures, and the temperature dependence of the molecular volume was analyzed by using crystal structure data and DFT calculations. The IL ionicity was investigated by Walden plots; according to this analysis, [Al(hfip)₄]⁻ ILs may be classified as “very good to good ILs”; while [C₂MIM][Al(hfip)₄] is a better IL than [C₂MIM][NTf₂]. The dielectric constants of ten [Al(hfip)₄]⁻ ILs were determined, and are unexpectedly high (ε_r=11.5 to 16.8). This could be rationalized by considering additional calculated dipole moments of the structures frozen in the solid state by DFT. The determination of hydrogen gas solubility in [Al(hfip)₄]⁻ RTILs by high-pressure NMR spectroscopy revealed very high hydrogen solubilities at 25 °C and 1 atm. These results indicate the significant potential of this class of ILs in manifold applications.

Modeling of the temperature-dependent liquid entropy of ionic liquids (ILs) with great accuracy using COSMO-RS is demonstrated. The minimum structures of eight IL ion pairs are investigated and the entropy, calculated from ion pairs, is found to differ on average only 2 % from the available experimental values (119 data points). For calculations with single ions, the average error amounts to 2.6 % and stronger-coordinating ions tend to give higher deviations. Additionally, the first parameterization of the standard liquid entropy for ILs is presented in the context of traditional volume-based thermodynamics (S_l⁰=1.585 kJ mol⁻¹ K⁻¹ nm⁻³⋅r_m³+14.09 J mol⁻¹ K⁻¹), which sheds light on the statistical treatment of ionic interactions. The findings provide the first direct access to accurate predictions of liquid entropies of ILs, which are tedious and time-consuming to measure.

Structures of the reactive intermediates (enamines and iminium ions) of organocatalysis with diarylprolinol derivatives have been determined. To this end, diarylprolinol methyl and silyl ethers, 1, and aldehydes, PhCH₂CHO, ^tBuCH₂CHO, PhCH=CHCHO, are condensed to the corresponding enamines, A and 3 (Scheme 2), and cinnamoylidene iminium salts, B and 4 (Scheme 3). These are isolated and fully characterized by melting/decomposition points, [α]_D, elemental analysis, IR and NMR spectroscopy, and high-resolution mass spectrometry (HR-MS). Salts with BF₄, PF₆, SbF₆, and the weakly coordinating Al[OC(CF₃)₃]₄ anion were prepared. X-Ray crystal structures of an enamine and of six iminium salts have been obtained and are described herein (Figs. 2 and 4–8, and Tables 2 and 7) and in a previous preliminary communication (Helv. Chim. Acta2008, 91, 1999). According to the NMR spectra (in CDCl₃, (D₆)DMSO, (D₆)acetone, or CD₃OD; Table 1), the major isomers 4 of the iminium salts have (E)-configuration of the exocyclic NC(1′) bond, but there are up to 11% of the (Z)-isomer present in these solutions (Fig. 1). In all crystal structures, the iminium ions have (E)-configuration, and the conformation around the exocyclic N-CC-O bond is synclinal-exo (cf.C and L), with one of the phenyl groups over the pyrrolidine ring, and the RO group over the π-system. One of the meta-substituents (Me in 4b, CF₃ in 4c and 4e) on a 3,5-disubstituted phenyl group is also located in the space above the π-system. DFT Calculations at various levels of theory (Tables 3–6) confirm that the experimentally determined structures (cf. Fig. 10) are by far (up to 8.3 kcal/mol) the most stable ones. Implications of the results with respect to the mechanism of organocatalysis by diarylprolinol derivatives are discussed.

Some ionic liquids (ILs) are structurally analogous to surfactants, especially those that consist of a combination of organic and inorganic ions. The critical micelle concentration (CMC) is a basic parameter of surface chemistry and colloid science. A significant amount of research has already been carried out to determine the CMCs of ILs. However, because of the many varied cation/anion combinations, it is a daunting task to measure the CMCs of all possible ILs. Herein we suggest a general rule for predicting the CMCs of ionic surfactants in water based on data from COSMO-RS calculations. In accordance with the Stauff–Klevens rule, the molecular volume (V_m) is sufficient to describe similar homologous series of cationic surfactants such as imidazolium- and ammonium-based ionic liquids with varying side-chain lengths. However, to also include anionic surfactants like Na[C_nSO₄] in a more general correlation, V_m has to be exchanged by the cubed molecular radius () and the molecular surface has to be used as an additional descriptor. Furthermore, to describe double amphiphilic compounds like [C₄MIm][C₈SO₄], the enthalpies of mixtures calculated by COSMO-RS have to be taken into account. The resulting equation had allowed us to predict the CMCs of all of the 36 tested surfactants with an error similar to or smaller than the usual experimental errors (18 different cations, 10 different anions: root mean squared error (rmse)=0.191 logarithmic units; R²=0.994). We discuss the factors governing micelle formation on the basis of our calculations and show that the structure of our equation can be related to Gibbs’ theory of crystallization.

Compounds including the free or coordinated gas-phase cations [Ag(η²-C₂H₄)_n]⁺ (n=1–3) were stabilized with very weakly coordinating anions [A]⁻ (A=Al{OC(CH₃)(CF₃)₂}₄, n=1 (1); Al{OC(H)(CF₃)₂}₄, n=2 (3); Al{OC(CF₃)₃}₄, n=3 (5); {(F₃C)₃CO}₃Al-F-Al{OC(CF₃)₃}₃, n=3 (6)). They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of ethene in CH₂Cl₂ solution. As a reference we also prepared the isobutene complex [(Me₂CCH₂)Ag(Al{OC(CH₃)(CF₃)₂}₄)] (2). The compounds were characterized by multinuclear solution-NMR, solid-state MAS-NMR, IR and Raman spectroscopy as well as by their single crystal X-ray structures. MAS-NMR spectroscopy shows that the [Ag(η²-C₂H₄)₃]⁺ cation in its [Al{OC(CF₃)₃}₄]⁻ salt exhibits time-averaged D_3h-symmetry and freely rotates around its principal z-axis in the solid state. All routine X-ray structures (2θ_max.<55°) converged within the 3σ limit at CC double bond lengths that were shorter or similar to that of free ethene. In contrast, the respective Raman active CC stretching modes indicated red-shifts of 38 to 45 cm⁻¹, suggesting a slight CC bond elongation. This mismatch is owed to residual librational motion at 100 K, the temperature of the data collection, as well as the lack of high angular data owing to the anisotropic electron distribution in the ethene molecule. Therefore, a method for the extraction of the CC distance in [M(C₂H₄)] complexes from experimental Raman data was developed and meaningful CC distances were obtained. These spectroscopic CC distances compare well to newly collected X-ray data obtained at high resolution (2θ_max.=100°) and low temperature (100 K). To complement the experimental data as well as to obtain further insight into bond formation, the complexes with up to three ligands were studied theoretically. The calculations were performed with DFT (BP86/TZVPP, PBE0/TZVPP), MP2/TZVPP and partly CCSD(T)/AUG-cc-pVTZ methods. In most cases several isomers were considered. Additionally, [M(C₂H₄)₃] (M=Cu⁺, Ag⁺, Au⁺, Ni⁰, Pd⁰, Pt⁰, Na⁺) were investigated with AIM theory to substantiate the preference for a planar conformation and to estimate the importance of σ donation and π back donation. Comparing the group 10 and 11 analogues, we find that the lack of π back bonding in the group 11 cations is almost compensated by increased σ donation.