Triethylbutylammonium bis(trifluoromethanesulphonyl)imide ionic liquid as an effective electrolyte additive for Li-ion batteries

Ionic liquids are promising additives for Li-ion batteries owing to its desirable physicochemical properties. Triethylbutylammonium bis(trifluoromethanesulphonyl)imide ([N₂₂₂₄][Tf₂N]) ionic liquid was synthesized and their physical and electrochemical properties were investigated. Among several quaternary ammonium ionic liquids, [N₂₂₂₄][Tf₂N] exhibited higher conductivity (1.31 mS?cm^?1), better thermal and electrochemical stabilities, and wide electrochemical window, i.e., more than 5.9 V. Standard solution was prepared by dissolving lithium bis(trifluoromethanesulphonyl)imide (LiTf₂N) in ethylene carbonates/dimethyl carbonate (1:1, by weight). The conductivity for the electrolyte containing [N₂₂₂₄][Tf₂N] and the mixed electrolyte without additives at 25 °C are 10.24 and 8.79 mS?cm^?1, respectively. LiFePO₄ half-cell containing 0.6 mol?L^?1 LiTf₂N-based organic electrolyte with [N₂₂₂₄][Tf₂N] showed relatively high initial discharge capacity and coulombic efficiency at first cycle. It is found that the mix [N₂₂₂₄][Tf₂N] electrolyte exhibits relatively high-rate capacity. The capacity retention of half-cell containing [N₂₂₂₄][Tf₂N] is 2 % more than without additive at 0.2 C. However, the rate capacity retention of the half-cell with mix [N₂₂₂₄][Tf₂N] electrolyte is above 10 % more than without additive at 0.5 C. The results showed that [N₂₂₂₄][Tf₂N] was an effective electrolyte additive in LiFePO₄ half-cell.     

Surface segregation in binary mixtures of imidazolium-based ionic liquids

Surface composition of binary mixtures of room-temperature ionic liquids has been investigated using time-of-flight secondary ion mass spectrometry at room temperature over a wide composition range. The imidazolium cations with longer aliphatic groups tend to segregate to the surface, and a bis(trifluoromethanesulfonyl)imide anion (Tf₂N^?) is enriched at the surface relative to hexafluorophosphate (PF₆^?). The surface of an equimolar mixture of Li[Tf₂N] and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) has a nominal composition of [bmim][Tf₂N] because of surface segregation and ligand exchange. The surface segregation of cations and anions is likely to result from alignment of specific ligand-exchanged molecules at the topmost surface layer to exclude more hydrophobic part of the molecules.     

Probing the adsorption of methylimidazole at ionic liquids/Cu electrode interface by surface‐enhanced Raman scattering spectroscopy

Two kinds of room‐temperature ionic liquids, 1‐butyl‐3‐methylimidazolium bromide ([BMIM]Br) and 1‐butyl‐3‐methylimidazolium tetrafluoroboride ([BMIM]BF₄), were used as solvent, and the adsorption of the ionic liquids themselves and of N‐methylimidazole (NMIM) were investigated by electrochemical surface‐enhanced Raman scattering (SERS) over a wide potential window. The results revealed that the cation of ionic liquid adsorbed onto Cu surface with different configurations in different potential ranges. When the potential was changed from the negative to the positive range, the orientation underwent a change from flat to vertical, and the onset potential for the orientation change was dependent on the types of anion of the ionic liquid. The ionic liquid in bulk solution exhibited a remarkable effect on the adsorption of NMIM. The electrode surface structure changed from adsorbing the ionic liquid at the negative potential to coadsorbing the ionic liquid and NMIM at relative positive potential for the [BMIM]BF₄ liquids, and formed films of NMIM at extremely positive potential. Due to the strong specific adsorption of Br⁻, the coadsorption of ionic liquid and NMIM was not observed in the system [BMIM]Br. By simulating the electrode surroundings, two surface complexes [Cu(NMIM)₄Br]Br·H₂O and [Cu(NMIM)₄](BF₄)₂ were synthesized by the electrochemical method in the corresponding ionic liquids for modeling the surface coordination chemistry of NMIM. The surface coordination configuration of NMIM and ionic liquids is proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

High‐pressure polarized Raman spectra of Gd2(MoO4)3: phase transitions and amorphization

Polarized Raman spectra of a single crystal of gadolinium molybdate [Gd₂(MoO₄)₃] were obtained between 1 atm and 7 GPa. Using a mixture of alcohols as the pressure‐transmitting medium, YY, ZZ, XY components of scattering matrices were measured. The ZZ spectra were also obtained in argon. Five phase transitions and amorphization were identified. The first and second transitions are reversible, while amorphization is not. In alcohol, amorphization is observed above 6.5 GPa. With argon as the pressure‐transmitting medium, amorphization is progressive and begins above 3 GPa. The spectral changes with pressure affect the high wavenumber bands attributed to symmetric and antisymmetric MoO₄ stretching modes as well as the very low wavenumber modes such as librations of the tetrahedra. This means that both short‐range and long‐range organizations of the tetrahedra are involved in these phase transitions. The amorphization mechanism and its dependence on the pressure‐transmitting medium are discussed, and the steric hindrance between polyhedra is believed to be the most relevant mechanism. The TO and LO low wavenumber modes of A₁ symmetry, observed in the Y(ZZ)Y and Z(YY)Z geometries, respectively, below 50 cm⁻¹, soften continuously through the first three phases when increasing pressure. The strong A₂ mode observed in the Z(XY)Z spectra exhibits the same anomalous behavior by decreasing from 53 to 46 cm⁻¹ at 2 GPa. The softening of these modes is related to the orientation change of tetrahedra observed by ab initio calculations when the volume of the cell is decreased. These orientation changes can explain the wavenumber decrease of the Mo O stretching modes above 2 GPa, which indicates an increase of Mo coordination. Copyright © 2010 John Wiley & Sons, Ltd.     

Electronic structures of imidazolium-based ionic liquids

Electronic structures of ionic liquids formed by 1-buthyl-3-alkylimidazolium ion [C_nmim]⁺ (n = 4 and 8) with various inorganic and organic anions have been investigated by ultraviolet photoemission, X-ray photoemission, inverse photoemission and soft X-ray emission spectroscopies (SXES). The comparison of the calculated density of states with the observed spectra revealed that the molecular orbital energies of these ionic liquids are significantly affected by the electrostatic Madelung potential among the ions. The SXES results clearly show that the both highest occupied and lowest unoccupied states of [C₄mim]⁺PF₆⁻ are derived from the cation as a result of strong Madelung potential. On the other hand, the SXES results show the valence electronic structures of ionic liquids with larger anion molecules, [C_nmim]⁺Tf₂N⁻ and [C_nmim]⁺OTf⁻ are contributed from the both cation and anion.     

Predicting the viscosity and electrical conductivity of ionic liquids on the basis of theoretically calculated ionic volumes

Selected physical properties of the ionic liquids might be quantitatively predicted based on the volumes of the ions these systems are composed of. It is demonstrated that the ionic volumes calculated using relatively simple theoretical quantum chemistry methods can be utilised to estimate the viscosities and electrical conductivities of various commonly used ionic liquids. The fitting formulas of the exponential form are offered and their predictive usefulness is verified. The quality of such predictions is discussed on the basis of several ionic liquids involving [Tf₂N]^? and [BF₄]^? anions and 16 various cations. The dependence of the viscosity and electrical conductivity of the ionic liquids on the temperature is also investigated and the temperature-dependent equations are derived and compared to the experimentally measured values.     

Pressure‐induced anomalous phase transformation in nano‐crystalline dysprosium sesquioxide

The phase transformation in nano‐crystalline dysprosium sesquioxide (Dy₂O₃) under high pressures is investigated using in situ Raman spectroscopy. The material at ambient was found to be cubic in structure using X‐ray diffraction (XRD) and Raman spectroscopy, while atomic force microscope (AFM) showed the nano‐crystalline nature of the material which was further confirmed using XRD. Under ambient conditions the Raman spectrum showed a predominant cubic phase peak at 374 cm⁻¹, identified as F_g mode. With increase in the applied pressure this band steadily shifts to higher wavenumbers. However, around a pressure of about 14.6 GPa, another broad band is seen to be developing around 530 cm⁻¹ which splits into two distinct peaks as the pressure is further increased. In addition, the cubic phase peak also starts losing intensity significantly, and above a pressure of 17.81 GPa this peak almost completely disappears and is replaced by two strong peaks at about 517 and 553 cm⁻¹. These peaks have been identified as occurring due to the development of hexagonal phase at the expense of cubic phase. Further increase in pressure up to about 25.5 GPa does not lead to any new peaks apart from slight shifting of the hexagonal phase peaks to higher wavenumbers. With release of the applied pressure, these peaks shift to lower wavenumbers and lose their doublet nature. However, the starting cubic phase is not recovered at total release but rather ends up in monoclinic structure. The factors contributing to this anomalous phase evolution would be discussed in detail. Copyright © 2010 John Wiley & Sons, Ltd.     

Conformational evolution of TFSI− in protic and aprotic ionic liquids

We here report on the conformational evolution of the bis(trifluoromethanesulfonyl)imide anion (TFSI⁻) in protic and aprotic TFSI⁻‐based ionic liquids as a function of temperature. The investigation is performed by Raman spectroscopy in the spectral ranges 240‐380 cm⁻¹ and 715‐765 cm⁻¹, where the interference from bands due to the cations is negligible. The contribution from each TFSI⁻ conformation, i.e. the cisoid (C₁) and the transoid (C₂), is quantified in order to estimate the enthalpy of conformational change, ΔH, which is found to be in the range 3.4–7.3 kJ/mol in the liquid state. Conformational information is for the first time determined from the 740 cm⁻¹ band, which previously mainly has been used as an indicator of ion‐ion interactions. The similarity in ΔH values obtained from the two spectral ranges demonstrates the validity of using also the 740 cm⁻¹ band for the quantification of the TFSI conformational evolution. Copyright © 2010 John Wiley & Sons, Ltd.     

Solvation of AgTFSI in 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid investigated by vibrational spectroscopy and DFT calculations

In this paper we investigate the solvation of silver bis(trifluoromethylsulfonyl)imide salt (AgTFSI) in 1‐ethyl‐3‐methylimidazolium TFSI [EMI][TFSI] ionic liquid by combining Raman and infrared (IR) spectroscopies with density functional theory (DFT) calculations. The IR and Raman spectra were measured in the 200–4000 cm⁻¹ spectral region for AgTFSI/[EMI][TFSI] solutions with different concentrations ([AgTFSI] <0.2 mole fraction). The analysis of the spectra shows that the spectral features observed by dissolution of AgTFSI in [EMI][TFSI] solution originate from interactions between the Ag⁺ cation and the first neighboring TFSI anions to form relatively stable Ag complexes. The ‘gas phase’ interaction energy of a type [Ag(TFSI)₃]²⁻ complex was evaluated by DFT calculations and compared with other interionic interaction energy contributions. The predicted spectral signatures because of the [Ag(TFSI)₃]²⁻ complex were assessed in order to interpret the main IR and Raman spectral features observed. The formation of such complexes leads to the appearance of new interaction‐induced bands situated at 753 cm⁻¹ in Raman and at 1015 and 1371 cm⁻¹ in IR, respectively. These specific spectral signatures are associated with the ‘breathing’ mode and the S–N–S and S–O stretching modes of the TFSI anions engaged in the complex. Finally, all these findings are discussed in terms of interaction mechanisms enabling the electrodeposition characteristics of silver from AgTFSI/[EMI][TFSI] IL‐based electrolytic solutions. Copyright © 2015 John Wiley & Sons, Ltd.     

ESR studies on the pressure and temperature dependence of electron self-exchange kinetics between tetrathiafulvalene (TTF) and its radical cation in ionic liquids and organic solvents

The question whether chemical reactions and diffusion processes in ionic liquids are comparable with those taking place in classical organic liquids is a current issue in the literature. Pressure- and temperature-dependent investigations on simple electron self-exchange reactions between the two partners of a redox couple are good tools to get a better understanding of how the solvent influences such reactions. The electron self-exchange reaction between tetrathiafulvalene (TTF) and its radical cation has been investigated in two ionic liquids and two organic solvents using electron spin resonance (ESR) line broadening experiments at variable temperature and pressure. Rate constants are reported for the ionic liquids 1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim⁺][Tf₂N^?]) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim⁺][Tf₂N^?]) within a temperature range of 298 K ≤ T ≤ 368 K and a pressure range of 0.1 MPa ≤ p ≤ 100 MPa. The self-exchange reaction of the redox couple [TTF/TTF^?+] has been found to be diffusion-controlled in the used ionic liquids over the entire temperature range. The observed rate constants in ionic liquids at higher pressures are larger than those predicted by common diffusion, and suggest that the electron transfer takes place within a solvent cage. Also, the self-exchange reaction of the [TTF/TTF^?+] redox couple in classical solvents (dimethylphthalate (DMP) and acetonitrile) was investigated and compared to the results with those obtained in ionic liquids. The high viscosity of the ionic liquids makes it difficult to extract the electron transfer rate constants reliably, making interpretation within the framework of the Marcus Theory impossible.     

Raman fingerprint of the interaction of K+ with the COO− group of zwitterionic alanine

The interaction of K⁺ with the zwitterionic form of alanine (ZAla) is investigated using Raman spectroscopy and density functional theory calculations. The Raman spectra of an aqueous solution of Ala and its mixture with KOH at different molar concentrations [ZAla + xKOH, x = 1–5 M] have been recorded in the spectral region 400–1800 cm⁻¹. The wavenumber position of the band at ~529 cm⁻¹ shows a red shift of 14 cm⁻¹, while the Raman band at ~634 cm⁻¹ shows a blue shift of 10 cm⁻¹ with the increasing x from 1 to 5 M. The intensity ratio I₆₃₄/I₅₂₉ is increased with increasing x, and it could be because of the increase in concentration of the [ZAla + K⁺] complex in the solution. The new Raman band appeared at ~1079 cm⁻¹ in the Raman spectra of [ZAla + xKOH, x = 1–5] complex. To determine the most probable site for the interaction of K⁺ with ZAla, the structures of ZAla and the [ZAla + K⁺] were optimized at B3LYP/6‐311++G(d,p) level of theory. The electrostatic potential calculation carried out for ZAla reveals that the maximum density of electron is lying over COO⁻, and therefore, COO⁻ would be the most probable site for the interaction of K⁺ with ZAla. The theoretically calculated Raman spectra of ZAla, [ZAla + K⁺] and the [ZAla⁻ + K⁺] are in good agreement with experimentally observed Raman spectra. Thus, the Raman bands at ~529, 634, and 1079 cm⁻¹ may be used as the Raman fingerprint for the interaction of K⁺ with COO⁻ of the ZAla and ZAla⁻. Copyright © 2015 John Wiley & Sons, Ltd.     

Lithium solvation in a PMMA membrane plasticized by a lithium‐conducting ionic liquid based on 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide

The Raman and Infrared (IR) spectra of poly(methyl methacrylate) (PMMA) membranes plasticized by ionic liquids of the (1 − x)[1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI)],xLiTFSI type, where BMI⁺ is the 1‐butyl‐3‐methylimidazolium cation and TFSI⁻ the bis(trifluoromethanesulfonyl)imide anion, are analyzed for a lithium bis(trifluoromethane sulfone)imide (LiTFSI) mole fraction x = 0.23 and PMMA contents from 0 to 50 wt%. The lithium is found to have an average coordination of about three CO groups and less than one TFSI⁻ anion. It plays the role of a cross‐linker between the ester groups of PMMA and the nonvolatile ionic liquid. Addition of PMMA to the (1 − x)(BMITFSI),xLiTFSI ionic liquid lowers the conductivity but might improve the lithium transference number by transforming the [Li(TFSI)₂]⁻ anionic clusters present in the pure ionic liquid into a mixed coordination by ester groups and TFSI⁻ anions. Copyright © 2008 John Wiley & Sons, Ltd.     

High‐pressure studies of the micro‐Raman spectra of iron cyanide complexes: Prussian blue (Fe4[Fe(CN)6]3), potassium ferricyanide (K3[Fe(CN)6]), and sodium nitroprusside (Na2[Fe(CN)5(NO)]·2H2O)

The pressure dependences of the peaks observed in the micro‐Raman spectra of Prussian blue (Fe₄[Fe(CN)₆]₃), potassium ferricyanide (K₃[Fe(CN)₆]), and sodium nitroprusside (Na₂[Fe(CN)₅(NO)]·2H₂O) have been measured up to 5.0 GPa. The vibrational modes of Prussian blue appearing at 201 and 365 cm⁻¹ show negative dν/dP values and Grüneisen parameters and are assigned to the transverse bending modes of the Fe C N Fe linkage which can contribute to a negative thermal expansion behavior. A phase transition occurring between 2.0 and 2.8 GPa in potassium ferricyanide is shown by changes in the spectral region 150–700 cm⁻¹. In the spectra of the nitroprusside ion, there are strong interactions between the FeN stretching mode and the FeNO bending and the axial CN stretching modes. The pressure dependence of the NO stretching vibration is positive, 5.6 cm⁻¹ GPa⁻¹, in contrast to the negative behavior in the iron(II)‐meso‐tetraphenyl porphyrinate complex. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman study of datolite CaBSiO4(OH) at simultaneously high pressure and high temperature

Using an in situ method of Raman spectroscopy and resistance‐heated diamond anvil cell, the system datolite CaBSiO₄(OH) – water has been investigated at simultaneously high pressure and temperature (up to Р ~5 GPa and Т ~250 °С). Two polymorphic transitions have been observed: (1) pressure‐induced phase transition or the feature in pressure dependence of Raman band wavenumbers at P = 2 GPа and constant T = 22 °С and (2) heating‐induced phase transition at T ~90 °С and P ~5 GPа. The number of Raman bands is retained at the first transition but changed at the second transition. The first transition is mainly distinguished by the changes in the slopes of pressure dependence of Raman peaks at 2 GPa. The second transition is characterized by several strong changes: the wavenumber jumps of major bands, the merging of strong doublets at 378 and 391 cm⁻¹ (values for ambient conditions), the splitting of the intermediate‐intensity band at 292 cm⁻¹, and the transformation of some low‐wavenumber bands at 160–190 cm⁻¹. No spectral and visual signs of overhydration and amorphization have been observed. No noticeable dissolution of datolite in the water medium occurred at 5 GPa and 250 °С after 3 h, which corresponds to typical conditions of the ‘cold’ zones of slab subduction. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of Ir(ppy)3 and [Ir(ppy)2 bpy]+ by infrared,Raman spectra and surface‐enhanced Raman scattering

The Raman and infrared spectra of fac ‐tris(2‐phenylpyridinato‐N,C2′)iridium(III), Ir(ppy)₃ and surface‐enhanced resonance Raman spectra of bis(2‐phenyl pyridinato‐) (2,2′bipyridine) iridium (III), [Ir(ppy)₂ (bpy)]⁺ cation were recorded in the wavenumber range 150–1700 cm⁻¹, and complete vibrational analyses of Ir(ppy)₃ and [Ir(ppy)₂ (bpy)]⁺ were performed. Most of the vibrational wavenumbers were calculated with density‐functional theory agree with experimental data. On the basis of the results of calculation and comparison of the spectra of both complexes and their analogue [Ru(bpy)₃]²⁺, we assign the vibrational wavenumbers for metal–ligand modes; metal–ligand stretching wavenumbers are 277/307 and 261/236 cm⁻¹ for Ir(ppy)₃, and 311/324, 257/270, 199/245 cm⁻¹ for [Ir(ppy)₂ bpy]⁺. Surface‐enhanced Raman scattering spectra of [Ir(ppy)₂ bpy]²⁺ were measured at two wavelengths on the red and blue edges of the low‐energy metal‐to‐ligand charge‐transfer band. According to the enhanced Raman intensities for the vibrational modes of both ligands ppy and bpy, the unresolved charge‐transfer band is deduced to consist of charge‐transfer transitions from the triplet metal to both ligands ppy and bpy. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigation of cation–anion interaction in 1‐(2‐hydroxyethyl)‐3‐methylimidazolium‐based ion pairs by density functional theory calculations and experiments

Gas‐phase structure, hydrogen bonding, and cation–anion interactions of a series of 1‐(2‐hydroxyethyl)‐3‐methylimidazolium ([HOEMIm]⁺)‐based ionic liquids (hereafter called hydroxyl ILs) with different anions (X = [NTf₂]^–, [PF₆]^–, [ClO₄]^–, [BF₄]^–, [DCA]^–, [NO₃]^–, [AC]^– and [Cl]^–), as well as 1‐ethyl‐3‐methylimizolium ([EMIm]⁺)‐based ionic liquids (hereafter called nonhydroxyl ILs), were investigated by density functional theory calculations and experiments. Electrostatic potential surfaces and optimized structures of isolated ions, and ion pairs of all ILs have been obtained through calculations at the Becke, three‐parameter, Lee–Yang–Parr/6‐31 + G(d,p) level and their hydrogen bonding behavior was further studied by the polarity and Kamlet–Taft Parameters, and ¹H‐NMR analysis. In [EMIm]⁺‐based nonhydroxyl ILs, hydrogen bonding preferred to be formed between anions and C2–H on the imidazolium ring, while in [HOEMIm]⁺‐based hydroxyl ILs, it was replaced by a much stronger one that preferably formed between anions and OH. The O–H···X hydrogen bonding is much more anion‐dependent than the C2–H···X, and it is weakened when the anion is changed from [AC]^– to [NTf₂]^–. The different interaction between [HOEMIm]⁺ and variable anion involving O–H···X hydrogen bonding resulted in significant effect on their bulk phase properties such as ¹H‐NMR shift, polarity and hydrogen‐bond donor ability (acidity, α). Copyright © 2011 John Wiley & Sons, Ltd.     

Lithium solvation and diffusion in the 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid

The Raman spectra of (1 − x)(BMITFSI), xLiTFSI ionic liquids, where 1‐butyl‐3‐methylimidazolium cation (BMI⁺) and bis(trifluoromethane‐sulfonyl)imide anion (TFSI⁻) are analyzed for LiTFSI mole fractions x < 0.4. As expected from previous studies on similar TFSI‐based systems, most lithium ions are shown to be coordinated within [Li(TFSI)₂]⁻ anionic clusters. The variation of the self‐diffusion coefficients of the ¹H, ¹⁹F, and ⁷Li nuclei, measured by pulsed‐gradient spin‐echo NMR (PGSE‐NMR) as a function of x, can be rationalized in terms of the weighted contribution of BMI⁺ cations, TFSI⁻ ‘free’ anions, and [Li(TFSI)₂]⁻ anionic clusters. This implies a negative transference number for lithium. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman and mid‐IR spectroscopic study of the magnesium carbonate minerals—brugnatellite and coalingite

Two hydrated hydroxy magnesium carbonate minerals brugnatellite and coalingite with a hydrotalcite‐like structure were studied by Raman spectroscopy. Intense bands are observed at 1094 cm⁻¹ for brugnatellite and at 1093 cm⁻¹ for coalingite attributed to the CO₃²⁻ν₁ symmetric stretching mode. Additional low intensity bands are observed at 1064 cm⁻¹. The existence of two symmetric stretching modes is accounted for in terms of different anion structural arrangements. Very low intensity bands at 1377 and 1451 cm⁻¹ are observed for brugnatellite, and the Raman spectrum of coalingite displays two bands at 1420 and 1465 cm⁻¹ attributed to the (CO₃)²⁻ν₃ antisymmetric stretching modes. Very low intensity bands at 792 cm⁻¹ for brugnatellite and 797 cm⁻¹ for coalingite are assigned to the CO₃²⁻ out‐of‐plane bend (ν₂). X‐ray diffraction studies by other researchers have shown that these minerals are disordered. This is reflected in the difficulty of obtaining Raman spectra of reasonable quality and explains why the Raman spectra of these minerals have not been previously or sufficiently described. A comparison is made with the Raman spectra of other hydrated magnesium carbonate minerals. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman spectrum of decrespignyite [(Y,REE)4Cu(CO3)4Cl(OH)5·2H2O] and its relation with those of other halogenated carbonates including bastnasite,hydroxybastnasite, parisite and northupite

Raman spectroscopy complemented with infrared spectroscopy has been used to study the rare‐earth‐based mineral decrespignyite [(Y,REE)₄Cu(CO₃)₄Cl(OH)₅· 2H₂O] and the spectrum compared with the Raman spectra of a series of selected natural halogenated carbonates from different origins including bastnasite, parisite and northupite. The Raman spectrum of decrespignyite displays three bands at 1056, 1070 and 1088 cm⁻¹ attributed to the CO₃²⁻ symmetric stretching vibration. The observation of three symmetric stretching vibrations is very unusual. The position of the CO₃²⁻ symmetric stretching vibration varies with the mineral composition. The Raman spectrum of decrespignyite shows bands at 1391, 1414, 1489 and 1547 cm⁻¹, whereas the Raman spectra of bastnasite, parisite and northupite show a single band at 1433, 1420 and 1554 cm⁻¹, respectively, assigned to the ν₃ (CO₃)²⁻ antisymmetric stretching mode. The observation of additional Raman bands for the ν₃ modes for some halogenated carbonates is significant in that it shows distortion of the carbonate anion in the mineral structure. Four Raman bands are observed at 791, 815, 837 and 849 cm⁻¹, which are assigned to the (CO₃)²⁻ν₂ bending modes. Raman bands are observed for decrespignyite at 694, 718 and 746 cm⁻¹ and are assigned to the (CO₃)²⁻ν₄ bending modes. Raman bands are observed for the carbonate ν₄ in‐phase bending modes at 722 cm⁻¹ for bastnasite, 736 and 684 cm⁻¹ for parisite and 714 cm⁻¹ for northupite. Multiple bands are observed in the OH stretching region for decrespignyite, bastnasite and parisite, indicating the presence of water and OH units in the mineral structure. Copyright © 2011 John Wiley & Sons, Ltd.     

Novel room temperature ionic liquid for fluorescence enhancement of Eu and Tb

The newly prepared ionic liquid, 1-butyl-3-methylimidazolium benzoate, ([bmim][BA]), was found to enhance the fluorescence of Eu³⁺ and Tb³⁺. The fluorescence enhancement resulted from a sensitization of the lanthanide fluorescence by the benzoate anion of the ionic liquid, [bmim][BA], and a reduction in the non-radiative channels in the non-aqueous environment provided by the ionic liquid. However, the fluorescence enhancement of the lanthanides in the ionic liquid was limited due to the operation of the inner filter effect, which resulted from the strong absorption of the benzoate. The inner filter effect was minimized by observing the Eu³⁺ fluorescence using a front face geometry and also by diluting the lanthanide-[bmim][BA] system, using another ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]), as a solvent. In the case of Tb³⁺, the emission from the lanthanide was masked by the strong emission from the ionic liquid in the region 450-580 nm. The long lived Tb³⁺ emission was therefore observed using delayed gated detection, where an appropriate delay was used to discriminate against the short lived emission from the ionic liquid. The large fluorescence enhancement due to ligand sensitized fluorescence observed with [bmim][BA] diluted in [bmim][Tf₂N], leads to nanomolar detection of the lanthanides. This is, to the best of our knowledge, the first report of an ionic liquid being employed for ligand sensitized fluorescence enhancement of lanthanides.