Cesium fluorohydrogenate, Cs(FH)2.3F

Cs(FH)_2.3F is a liquid salt exhibiting a low viscosity of 20.1 cP and a high conductivity of 86.3 mS cm⁻¹ at 25 °C, in spite of the relatively high melting point (16.9 °C). The high density of 2.82 g cm⁻³ at the liquid state is due to the heavy atomic weight and small size of cesium atom compared to the organic cations of general ionic liquids. The infrared spectroscopy indicates that this salt contains (FH)₂F⁻ as a main anionic species. The other anionic species such as (FH)₃F⁻ found in the cases of other M⁺(HF)_2.3F (M = a univalent organic cation) ionic liquid salts is not detected, suggesting its small abundance as well as the presence of neutral HF in the form of molecular and/or oligomers. The result of ¹H NMR also suggests that the anions exchange HF between them. These observations coincide with the experimental result that Cs(FH)_2.3F acts as an acid against general ionic liquid fluorohydrogenates such as EMIm(FH)_2.3F (EMIm = 1-ethyl-3-methylimidazolium) to lose HF and give Cs(FH)₂F precipitate.     

Room temperature molten fluorometallates: 1-ethyl-3-methylimidazolium hexafluoroniobate(V) and hexafluorotantalate(V)

The first room temperature molten salts containing hexafluorometallate anions of transition metals, 1-ethyl-3-methylimidazolium (EMIm) hexafluoroniobate, EMImNb(V)F₆, and hexafluorotantalate, EMImTa(V)F₆, have been synthesized by the reactions of EMImF·2.3HF with NbF₅ and TaF₅, respectively. They exhibit similar physical properties. Viscosities and conductivities are 49 cP and 8.5 mS cm⁻¹ for EMImNbF₆ and 51 cP and 7.1 mS cm⁻¹ for EMImTaF₆, respectively at 298 K.     

A new room temperature ionic liquid of oxyfluorometallate anion: 1-Ethyl-3-methylimidazolium oxypentafluorotungstate (EMImWOF5)

The first room temperature ionic liquid (room temperature molten salt) containing oxyfluorometallate anion, 1-ethyl-3-methylimidazolium oxypentafluorotungstate (EMImWOF₅), has been synthesized and characterized compared to other known EMIm fluorocomplex salts. EMImWOF₅ is synthesized by two routes: one is the hydrolysis of EMImWF₇ and the other is the fluoroacid-base reaction of EMIm(HF)_2.3F and WOF₄. EMImWOF₅ is a hydrophilic room temperature ionic liquid but is stable in aqueous solution. From the result of DSC analysis, EMImWOF₅ exhibits a glass transition at 182 K and melts at 253 K. The density, conductivity and viscosity at 298 K are 2.25 g cm⁻³, 3.0 mS cm⁻¹ and 105.1 cP, respectively.     

Influence of hydrofluoric acid on extraction of thorium using a commercially available extraction chromatographic resin

The dependence of Th recovery on hydrofluoric acid (HF) concentration in nitric acid (HNO₃) solutions (1–5 mol/dm³) containing 1 × 10⁻⁶ mol/dm³ of Th and various concentrations of HF and the elution behavior were studied using a commercially available UTEVA (for uranium and tetravalent actinide) resin column. Thorium recovery decreased with an increase in HF concentration in the sample solutions. The concentration of HF at which Th recovery started to decrease was ∼1 × 10⁻⁴ mol/dm³ in 1 mol/dm³ HNO₃ solution, ∼1 × 10⁻³ mol/dm³ in 3 mol/dm³ HNO₃ solution, and ∼1 × 10⁻² mol/dm³ in 5 mol/dm³ HNO₃ solution. When Al(NO₃)₃ (0.2 mol/dm³) or Fe(NO₃)₃ (0.6 mol/dm³) was added as a masking agent for F⁻ to the Th solution containing 1 × 10⁻¹ mol/dm³ HF and 1 mol/dm³ HNO₃, Th recovery improved from 1.4 ± 0.3% to 95 ± 5% or 93 ± 3%. Effective extraction of Th using UTEVA resin was achieved by selecting the concentration of HNO₃ and/or adding masking agents such as Al(NO₃)₃ according to the concentration of HF in the sample solution.     

Multi-pumping flow system for the determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples

A multi-pumping flow system (MPFS) for the spectrophotometric determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples is proposed. The determination of orthophosphate is based on the vanadomolybdate method. In-line ultraviolet photo-oxidation is employed to mineralise organic phosphorus to orthophosphate prior to detection. A solenoid valve allows the deviation of the flow towards the UV-lamp to carry out the determination of organic phosphorus.Calibration was found to be linear up to 20 mg P L⁻¹, with a detection limit (3s_b/S) of 0.08 mg P L⁻¹, an injection throughput of 75 injections h⁻¹ and a repeatability (R.S.D.) of 0.6% for the direct determination of orthophosphate. On the other hand, calibration graphs were linear up to 40 mg P L⁻¹, with a detection limit (3s_b/S) of 0.5 mg P L⁻¹, an injection throughput of 11 injections h⁻¹ and a repeatability (R.S.D.) inferior to 2.3% for the procedures involving UV photo-oxidation.     

Investigation of Fe-based oxyhydroxy-fluoride with hollandite-type structure

Well crystallized Fe-based oxyhydroxy-fluoride with the FeO(OH_0.2F_0.8)·0.2H₂O chemical composition has been prepared from hydrolysis of Fe trifluoride under supercritical CO₂ conditions. Investigation by Mössbauer spectroscopy and neutron diffraction show that this compound crystallize in the monoclinic symmetry (SG: I2/m, a = 10.447(7) Å, b = 3.028(2) Å, c = 10.445(4) Å, β = 90.00(3)°). Taking into account the Fe-O(F) bond distances, F⁻ anions are mainly located on the common vertices of Fe octahedra whereas OH⁻ groups occupy mainly the shared edges of the Fe octahedra. Two various highly distorted octahedral sites have been identified with Fe-O/F bond distances varying from 1.90 Å to 2.31 Å. One Fe site is more distorted than in FeO_0.8OH_1.2·0.2Cl akaganeite because of the random distribution of F⁻/OH⁻/O²⁻ in the vicinity of this Fe cation.     

Structural and vibrational characterization of [KrF][AuF6] and α-[O2][AuF6] using single crystal X-ray diffraction, Raman spectroscopy and electron structure calculations

The salt [KrF][AuF₆] has been prepared by the direct oxidation of gold powder in anhydrous HF at 20 °C using the potent oxidative fluorinating agent KrF₂. The KrF⁺ salt readily oxidizes molecular oxygen at ambient temperature to yield [O₂][AuF₆]. Variable temperature Raman spectroscopy has been used to identify a reversible phase transition in [O₂][AuF₆], which occurs between −114 and −118 °C. Single crystal X-ray diffraction has been used to characterize the low-temperature, α-phase of [O₂][AuF₆]. The phase transition is attributed to ordering of the O₂⁺ cation in the crystal lattice, which is accompanied by minor distortions of the AuF₆⁻ anion. The α-phase of [O₂][AuF₆] crystallizes in the triclinic space group , with a=4.935(6) Å, b=4.980(6) Å, c=5.013(6) Å, α=101.18(1)°, β=90.75(2)°, γ=101.98(2)°, V=342.97 Å³, Z=1, and R₁=0.0481 at −122 °C. The structure of the precursor, [KrF][AuF₆], has also been determined by single crystal X-ray diffraction and crystallizes in the monoclinic space group Cc with a=7.992(3) Å, b=7.084(3) Å, c=10.721(4) Å, β=105.58(1)°, V=584.8(4) Å³, Z=4 and R₁=0.0389 at −125 °C. The KrF⁺ and AuF₆⁻ ions interact by means of a FKr---FAu fluorine bridge that is bent by 125.3(7)° about the bridge fluorine. The KrF_t and Kr---F_b bond lengths in [KrF][AuF₆] were determined to be 1.76(1) and 2.15(1) Å, respectively. The energy minimized structures of the [KrF][AuF₆] ion-pair and the AuF₆⁻ anion have been determined at the Hartree-Fock (HF), MP2 and local density functional (LDF) levels of theory. These calculations have also been used to assign the vibrational spectrum of the [KrF][AuF₆] ion-pair in greater detail and to reassign the vibrational spectrum of the AuF₆⁻ anion.     

Comparison of microwave-assisted digestion procedures for total trace element content determination in calcareous soils

The aim of the study was to determine total trace (Cd, Co, Cr, Cu, Mn, Pb and Zn) and major (Al and Fe) element concentrations in calcareous soils using microwave-assisted digestion procedures. The literature showing lack of consensus regarding digestion procedures and unsatisfying recoveries for calcareous materials, four procedures using various acid combinations (HCl, HNO₃, H₂O₂, HF) and volumes were tested using a certified reference material (CRM 141R) and natural calcareous soil samples. Digests were analysed by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Repeatability (R.S.D. <5%) and recoveries (82-116%) showed that the procedures were precise and accurate for most elements. Five calcareous soil samples from a Champagne vineyard plot were, then, subjected to these procedures. In calcareous materials, the presence of HF resulted in Al being severely underestimated (recovery <5%) and Co overestimated (recovery >124%) due to complex formation or spectrochemical interferences, respectively. As digestion was not significantly influenced by the addition of H₂O₂, the procedure corresponding to Aqua regia (HCl-HNO₃) appeared as the best compromise and was selected for further multielemental environmental studies on calcareous materials, even if the absence of HF could lead to incomplete digestion of accessory silicate minerals. Results for a vineyard plot showed that the soils were contaminated (3.65 mg kg⁻¹ Cd, 67 mg kg⁻¹ Cr, 278 mg kg⁻¹ Cu, 143 mg kg⁻¹ Pb and 400 mg kg⁻¹ Zn) as a consequence of urban waste and copper-treatment applications.     

Determination of total nitrogen in atmospheric wet and dry deposition samples

A microwave-assisted persulfate oxidation method followed by ion chromatographic determination of nitrate was developed for total nitrogen determination in atmospheric wet and dry deposition samples. Various operating parameters such as oxidation reagent concentrations, microwave power, and extraction time were optimized to maximize the conversion of total nitrogen to nitrate for subsequent chemical analysis. Under optimized conditions, 0.012 M K₂S₂O₈ and 0.024 M NaOH were found to be necessary for complete digestion of wet and dry deposition samples at 400 W for 7 min using microwave. The optimized extraction method was then validated by testing different forms of organic nitrogen loaded to pre-baked filter substrates and NIST SRM 1648 (urban particulate matter), and satisfactory results were obtained. In the case of wet deposition samples, standard addition experiments were performed. The suitability of the method for real-world application was assessed by analyzing a number of wet and dry deposition samples collected in Singapore during the period of March-April 2007. The organic nitrogen content was 15% (wet) and 30% (dry) of the total nitrogen. During the study period, the estimated wet fluxes for nitrate (NO₃⁻), ammonium (NH₄⁺), organic nitrogen (ON), and total nitrogen (TN) were 16.1 ± 6.5 kg ha⁻¹ year⁻¹, 11.5 ± 5.7 kg ha⁻¹ year⁻¹, 3.8 ± 1.5 kg ha⁻¹ year⁻¹and 31.5 ± 13.2 kg ha⁻¹ year⁻¹, respectively, while the dry fluxes were 2.5 ± 0.8 kg ha⁻¹ year⁻¹, 1.4 ± 0.9 kg ha⁻¹ year⁻¹, 2.3 ± 1.4 kg ha⁻¹ year⁻¹ and 7.5 ± 2.6 kg ha⁻¹ year⁻¹, respectively.     

Determination of water-soluble inorganic and organic species in atmospheric fine particulate matter

The use of ion chromatography (IC) in conjunction with ultrasonic extraction is described for the routine analysis of water-soluble major inorganic ions and organic acids in atmospheric fine particles (PM_2.5). Both the extraction method and the IC analysis were validated using NIST SRM 1648 (urban particulate matter). In addition, the reliability of the IC method was established by intercomparison of results obtained with those from suitable alternative analytical techniques (atomic absorption spectrometry (AAS), proton-induced X-ray emission (PIXE) spectrometry, and UV-Visible spectrophotometry). The validated IC method was successfully applied for field monitoring of PM_2.5 particles collected in Singapore over an extended period of time. The IC analysis revealed that the concentrations of individual ions were in the order, SO₄²⁻ > NH₄⁺ > NO₃⁻ > Na⁺ > K⁺ > Cl⁻, respectively. Among the major ionic components, SO₄²⁻ contributed 50% to the measured water-soluble aerosol mass followed by NH₄⁺ (16.5%) and NO₃⁻ (9.0%). The cations Na⁺, K⁺, Mg²⁺, and Ca²⁺ accounted for 24% of the total water-soluble mass. The IC analysis was performed to quantify the organic acids, which typically account for a small fraction of water-soluble organic compounds in PM_2.5. Oxalate was found to be the dominant species among the organic acids measured in this work.     

Single-run ion chromatographic separation of inorganic and low-molecular-mass organic anions under isocratic elution: Application to environmental samples

For the isocratic ion chromatography (IC) separation of low-molecular-mass organic acids and inorganic anions three different anion-exchange columns were studied: IonPac AS14 (9 μm particle size), Allsep A-2 (7 μm particle size), and IC SI-50 4E (5 μm particle size). A complete baseline separation for all analyzed anions (i.e., F⁻, acetate, formate, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, HPO₄²⁻ and SO₄²⁻) in one analytical cycle of shorter than 17 min was achieved on the IC SI-50 4E column, using an eluent mixture of 3.2 mM Na₂CO₃ and 1.0 mM NaHCO₃ with a flow rate of 1.0 mL min⁻¹. On the IonPac AS14 column, it was possible to separate acetate from inorganic anions in one run (i.e., less than 9 min), but not formate, under the following conditions: 3.5 mM Na₂CO₃ plus 1.0 mM NaHCO₃ with a flow rate of 1.2 mL min⁻¹. Therefore, it was necessary to adapt a second run with a 2.0 mM Na₂B₄O₇ solution as an eluent under a flow rate of 0.8 mL min⁻¹ for the separation of organic ions, which considerably enlarged the analysis time. For the Allsep A-2 column, using an eluent mixture of 1.2 mM Na₂CO₃ plus 1.5 mM NaHCO₃ with a flow rate of 1.6 mL min⁻¹, it was possible to separate almost all anions in one run within 25 min, except the fluoride-acetate critical pair. A Certified Multianion Standard Solution PRIMUS for IC was used for the validation of the analytical methods. The lowest RSDs (less than 1%) and the best LODs (0.02, 0.2, 0.16, 0.11, 0.06, 0.05, 0.04, 0.14 and 0.09 mg L⁻¹ for F⁻, Ac⁻, For⁻, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, HPO₄²⁻ and SO₄²⁻, respectively) were achieved using the IC SI-50 4E column. This column was applied for the separation of concerned ions in environmental precipitation samples such as snow, hail and rainwater.     

Intra-cluster proton transfer in anilide-(HF)n (n = 1-4): Can the size of HF cluster influence the N?H-F → N-H?F switching

The impact of the HF cluster size on the proton-transfer switch between N⁻?H-F and N-H?F⁻ in the anilide-(HF)_n = 1-4 complexes was investigated by means of the quantum chemical methods. The change in the H-bond strength due to variation of the HF cluster size was well monitored by change in the binding energy (BE), structural parameter, electron density topology, natural charge and charge transfer. For n = 1, our results at the MP2/6-311++G(2d,2p) level show that the minimum-energy structure corresponds to the H-bonded complex PhNH⁻?HF with excess negative charge localized on the N atom of the anilide anion. For n > 1, minimum energy structures correspond to PhNH₂?F⁻(HF)_1-3 ones, namely a solvated F⁻ ion. This is a case in which the relative change in the acidity of the HF is observed in the ground state as the size of cluster increases. The nature of the weak interactions in the complexes was characterized by means of atoms in molecules (AIM) and the natural bond orbital (NBO) analyses.     

Direct estimation of nitrate, total and fractionated water extractable organic carbon (WEOC) in an agricultural soil using direct UV absorbance deconvolution

In this study, a multiwavelength UV spectral deconvolution (UVSD) procedure is proposed as a robust and simple procedure for direct estimation of carbon and nitrate contents in soil water extracts. Soil samples were collected from an open-air field cultivated with maize at 3 different depths, 30 cm each, between 0 and 90 cm of soil surface during a period of 7 months. Fractionation of water extractable organic carbon (WEOC) into hydrophobic (Hpo-WEOC), transphilic (Tpi-WEOC), and hydrophilic (Hpi-WEOC) fractions is performed using XAD-8 and XAD-4 resins connected in series. In order to perform UVSD, 3 representative reference spectra of WEOC fractions were selected automatically, in addition to a 4th spectrum representative of NO₃⁻ selected manually in order to compose the deconvolution basis. The restitution of UV spectra was made in the range 235-350 nm. Through exploitation of soil water extract UV spectra, it was possible in a single-step deconvolution procedure to determine the organic carbon (mg C l⁻¹) and NO₃⁻ (mg l⁻¹) concentrations and to differentiate and to quantitatively estimate carbon content of WEOC fractions. Statistical tests indicated satisfactory correlations between values estimated using UVSD and those determined by conventional reference methods for each parameter determined. The ranges of concentrations of carbon and NO₃⁻ in the soil water extracts studied are between 3.00 and 15.00 mg C l⁻¹ and 60-300 mg l⁻¹, respectively. The limits of quantification (LQ) and of detection (LD) of WEOC and NO₃⁻ were found to be 0.10 and 0.05 mg C l⁻¹, and 0.10 and 0.03 mg l⁻¹, respectively.     

Sequential injection methodology for carbon speciation in bathing waters

A sequential injection method (SIA) for carbon speciation in inland bathing waters was developed comprising, in a single manifold, the determination of dissolved inorganic carbon (DIC), free dissolved carbon dioxide (CO₂), total carbon (TC), dissolved organic carbon and alkalinity. The determination of DIC, CO₂ and TC was based on colour change of bromothymol blue (660 nm) after CO₂ diffusion through a hydrophobic membrane placed in a gas diffusion unit (GDU). For the DIC determination, an in-line acidification prior to the GDU was performed and, for the TC determination, an in-line UV photo-oxidation of the sample prior to GDU ensured the conversion of all carbon forms into CO₂. Dissolved organic carbon (DOC) was determined by subtracting the obtained DIC value from the TC obtained value. The determination of alkalinity was based on the spectrophotometric measurement of bromocresol green colour change (611 nm) after reaction with acetic acid. The developed SIA method enabled the determination of DIC (0.24–3.5 mg C L⁻¹), CO₂ (1.0–10 mg C L⁻¹), TC (0.50–4.0 mg C L⁻¹) and alkalinity (1.2–4.7 mg C L⁻¹ and 4.7–19 mg C L⁻¹) with limits of detection of: 9.5 μg C L⁻¹, 20 μg C L⁻¹, 0.21 mg C L⁻¹, 0.32 mg C L⁻¹, respectively. The SIA system was effectively applied to inland bathing waters and the results showed good agreement with reference procedures.     

Protonated MF3 (M = N-Bi): Structure, stability, and thermochemistry of the H-MF3 and HF-MF2 isomers

The structure, stability, and thermochemistry of the H(MF₃)⁺ isomers (M = N-Bi) have been investigated by MP2 and coupled cluster calculations. All the HF-MF₂⁺ revealed weakly bound ion-dipole complexes between MF₂⁺ and HF. For M = N, As, Sb, and Bi they are more stable than the H-MF₃⁺ covalent structures (free energy differences) by 6.3, 14.3, 32.1, and 73.5 kcal mol⁻¹, respectively. H-PF₃⁺ is instead more stable than HF-PF₂⁺ by 21.8 kcal mol⁻¹. The proton affinities (PAs) of MF₃ at the M atom range from 91.9 kcal mol⁻¹ (M = Bi) to 156.5 kcal mol⁻¹ (M = P), and follow the irregular periodic trend BiF₃ < SbF₃ < AsF₃ < NF₃ < PF₃. The PAs at the F atom range instead from 131.9 kcal mol⁻¹ (M = P) to 164.9 kcal mol⁻¹ (M = Bi), and increase in the more regular order PF₃ ≈ NF₃ < AsF₃ < SbF₃ < BiF₃. This trend parallels the fluoride-ion affinities of the MF₂⁺ cations. For protonated NF₃ and PF₃, the calculations are in good agreement with the available experimental results. As for protonated AsF₃, they support the formation of HF-AsF₂⁺ rather than the previously proposed H-AsF₃⁺. The calculations indicate also that the still elusive H(SbF₃)⁺ and H(BiF₃)⁺ should be viable species in the gas phase, exothermically obtainable by various protonating agents.     

Ultra-sensitive determination of cyanide in surface water by gas chromatography–tandem mass spectrometry after derivatization with 2-(dimethylamino)ethanethiol

A gas chromatography–tandem mass spectrometric (GC–MS/MS) method has been established for the determination of cyanide in surface water. This method is based on the derivatization of cyanide with 2-(dimethylamino)ethanethiol in surface water. The following optimum reaction conditions were established: reagent dosage, 0.7 g L⁻¹ of 2-(dimethylamino)ethanethiol; pH 6; reaction carried out for 20 min at 60 °C. The organic derivative was extracted with 3 mL of ethyl acetate, and then measured by using GC–MS/MS. Under the established conditions, the detection and quantification limits were 0.02 μg L⁻¹ and 0.07 μg L⁻¹ in 10-mL of surface water, respectively. The calibration curve had a linear relationship relationship with y = 0.7140x + 0.1997 and r² = 0.9963 (for a working range of 0.07–10 μg L⁻¹) and the accuracy was in a range of 98–102%; the precision of the assay was less than 7% in surface water. The common ions Cl⁻, F⁻, Br⁻, NO₃⁻, SO₄²⁻, PO₄³⁻, K⁺, Na⁺, NH₄⁺, Ca²⁺, Mg²⁺, Ba²⁺, Mn⁴⁺, Mn²⁺, Fe³⁺, Fe²⁺ and sea water did not interfere in cyanide detection, even when present in 1000-fold excess over the species. Cyanide was detected in a concentration range of 0.07–0.11 μg L⁻¹ in 6 of 10 surface water samples.     

Potentiometric sensor using sub-micron Cu2O-doped RuO2 sensing electrode with improved antifouling resistance

A Cu₂O-doped RuO₂ sensing electrode (SE) for potentiometric detection of dissolved oxygen (DO) was prepared and its structure and electrochemical properties were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron microscopy (XPS) and energy-dispersive spectroscopy (EDS) techniques. Cu₂O-RuO₂-SE displayed a linear DO response from 0.5 to 8.0 ppm (log[O₂], −4.73 to −3.59) within a temperature range of 9-30 °C. The maximum sensitivity of −47.4 mV/decade at 7.27 pH was achieved at 10 mol% Cu₂O. Experimental evaluation of the Cu₂O-doped RuO₂-SE demonstrated that the doping of RuO₂ not only improves its structure but also enhances both sensor's selectivity and antifouling properties. Selectivity measurements revealed that 10 mol% Cu₂O-doped RuO₂-SE is insensitive to the presence of Na⁺, Mg²⁺, K⁺, Ca²⁺, NO₃⁻, PO₄²⁻ and SO₄²⁻ ions in the solution in the concentration range of 10⁻⁷-10⁻¹ mol/l.     

Determination of fluoride and oxalate using the indicator reaction of Zr(IV) with methylthymol blue adsorbed on silica gel

Solid-phase spectrophotometric and visual test-methods of fluoride and oxalate determination are proposed. The methods are based on the competitive reactions of ZrOCl₂ with methylthymol blue immobilized on silica gel and fluoride or oxalate in solution. Absorbance of the solid-phase reagent at 590 nm decreases with the growth of fluoride and oxalate contents in solution. The developed methods demonstrate high selectivity. The interference of Bi(III) and SO₄²⁻, PO₄³⁻ is eliminated by the addition of 0.01 mol L⁻¹ solution of ascorbic acid and 0.01 mol L⁻¹ of BaCl₂, respectively. To eliminate the fluoride interference with oxalate determination 1 × 10⁻³ mol L⁻¹ solution of Ca(NO₃)₂ at pH 1.5 was added. The anions of the organic acids were destructed prior to F⁻ determination by ultrasonic exposition (44 kHz, intensity of ≤10 W cm⁻² for 3 min). The proposed methods were applied to the analysis of mineral water, toothpaste and biological fluids.     

Thermal properties of N-alkyl-N-methylpyrrolidinium and N-butylpyridinium fluorometallates and physicochemical properties of their melts

A series of N-alkyl-N-methylpyrrolidinium (RMPyr⁺, where R = E: ethyl, B: butyl, and H: hexyl) and N-butylpyridinium (BPy⁺) salts based on the fluorocomplex anions, BF₄⁻, PF₆⁻, SbF₆⁻, NbF₆⁻, TaF₆⁻, and WF₇⁻, have been synthesized and their thermal behavior has been investigated. The melting points of the RMPyr⁺ salts are above room temperature with the trend; BMPyrAF₆ < HMPyrAF₆ < EMPyrAF₆ for the hexafluorocomplex salts. Some of the salts containing BMPyr⁺ and HMPyr⁺ exhibit phase transitions in the solid states. Similar melting points of BPy⁺ salts of PF₆⁻, SbF₆⁻, NbF₆⁻, TaF₆⁻, and WF₇⁻ are observed at around 350 K. Ionic conductivity and viscosity for BMPyrNbF₆ (3.0 mS cm⁻¹ and 164 cP at 328 K) are similar to those for BMPyrTaF₆ (3.0 mS cm⁻¹ and 165 cP at 328 K), resulting from the similarity of the anions in size. The activation energies of ionic conductivity for the NbF₆⁻ and TaF₆⁻ salts are 18 and 20 kJ mol⁻¹, and those for viscosity are 23 and 25 kJ mol⁻¹, respectively calculated by Arrhenius equation in the temperature range between 328 and 348 K. Electrochemical windows of BMPyrNbF₆, BMPyrTaF₆, and BMPyrWF₇ are about 4.0, 5.0 and 3.1 V, respectively.