1,2,4-triazolium-cation-based energetic salts

3,4,5-Triamino-1,2,4-triazole (guanazine, 1) can be readily methylated with methyl iodide yielding methylguanazinium iodide (2). Salts containing the novel methylguanazinium cation with energetic anions were synthesised by metathesis reactions with silver azide (3), silver nitrate (4), silver perchlorate (5), sodium 5,5'-azotetrazolate (6), silver 5-nitrotetrazolate (7) and silver dinitramide (8), yielding a new family of heterocycle-based salts, which were fully characterised by analytical (mass spectrometry and elemental analysis) and spectroscopic methods (IR, Raman and NMR). In addition, the molecular structures of all compounds were confirmed by X-ray analysis, revealing extensive hydrogen-bonding in the solid state and densities between 1.399 (3) and 1.669 g cm(-3) (5). The hydrogen-bonded ring motifs are discussed in the formalism of graph-set analysis for hydrogen-bond patterns and compared to each other. Preliminary sensitivity testing of the crystalline compounds indicate surprisingly low sensitivities to both friction and impact, the highest friction and shock sensitivity being found for the perchlorate (5, 220 N) and the dinitramide (8, 20 J) salts, respectively. In addition, DSC analysis was used to assess the thermal stabilities of the compounds: 3-6 melt above 200 degrees C with concomitant decomposition, whereas 7 and 8 have clearly defined melting points at 162 and 129 degrees C, respectively, and with decomposition occurring about 30 degrees C above the melting point. Lastly all compounds have positive calculated heats of formation between 336 (4) and 4070 kJ kg(-1) (6) and calculated detonation velocities in the range between 8330 (7) and 8922 m s(-1) (6) making them of interest as new highly energetic materials with low sensitivity.     

The first 1-alkyl-3-perfluoroalkyl-4,5- dimethyl-1,2,4-triazolium salts

Syntheses of quaternary 1-alkyl-3-perfluoroalkyl-4,5-dimethyl-1,2,4-triazolium iodides have led to a variety of new quaternary salts via metathesis reactions. 1,4,5-Trimethyl-3-trifluoro-methyl-1,2,4-triazolium iodide (6) with LiN(SO(2)CF(3))(2), KSO(3)CF(3), AgClO(4), AgBF(4); 1-(3-fluoropropyl)-3-trifluoromethyl-4,5-dimethyl-1,2,4-triazolium iodide (7) with LiN(SO(2)CF(3))(2); and 1,4,5-trimethyl-3-perfluorooctyl-1,2,4-triazolium iodide (8) with LiN(SO(2)CF(3))(2), AgClO(4), AgBF(4) gave excellent yields of new thermally stable and relatively low melting quaternary salts. The structure of 1,4,5-trimethyl-3-perfluorooctyl-1,2,4-triazolium tetrafluoroborate (11c) was confirmed by single-crystal X-ray analysis. Although the molecular weight of 11c (cation) is 3-fold greater than that of the 3-trifluoromethyl derivative 9d, its melting point is 32 degrees C lower.     

Designer ionic liquid crystals based on congruently shaped guanidinium sulfonates

Ionic liquid crystals are mesogenic compounds that consist of cations and anions, usually rod-like cations and spherical anions. Herein we report a new method for the synthesis of ionic liquid crystals by using cations and anions of the same molecular shape with oppositely charged head groups. Thus, 4-alkoxyphenylpentamethylguanidinium 4-alkoxyphenylsulfonate ion pairs have been synthesised. 4-Alkoxyphenylpentamethylguanidinium iodides were also prepared to determine the influence of congruently shaped anions, in comparison with their spherical counterparts, on mesophase behaviour, which was investigated by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). All the liquid crystalline salts exhibit smectic A mesophases with strongly interdigitated bilayer structures. The guanidinium sulfonate ion pairs show mesomorphic properties from shorter alkyl chain lengths (≥C(9)) and lower melting points (≈10 K), whereas the corresponding guanidinium iodides are liquid crystalline for longer alkyl chain lengths (≥C(14)). For chains with ≥C(18), however, the mesophase range decreases for the sulfonate ion pairs, but not for the iodide salts.     

Quaternary trialkyl(polyfluoroalkyl)ammonium salts including liquid iodides

New quaternary ammonium salts that contain polyfluorinated alkyl substituents were prepared by the polyfluoroalkylation of tertiary amines with polyfluorinated alkyl iodides. Metathesis reactions of the iodide salts with fluorine-containing anions resulted in new low melting salts. The iodide salts of the tri(isooctyl)polyfluoroalkyl amines are also liquids at 25°C.     

Dependence of solar cell performance on the nature of alkaline counterion in gel polymer electrolytes containing binary iodides

Performance of dye-sensitized nano-crystalline TiO₂ thin film-based photo-electrochemical solar cells (PECSCs) containing gel polymer electrolytes is largely governed by the nature of the cation in the electrolyte. Dependence of the photovoltaic performance in these quasi-solid state PECSCs on the alkaline cation size has already been investigated for single cation iodide salt-based electrolytes. The present study reports the ionic conductivity dependence on the nature of alkaline cations (counterion) in a gel polymer electrolyte based on binary iodides. Polyacrylonitrile-based gel polymer electrolyte series containing binary iodide salts is prepared using one of the alkaline iodides (LiI, NaI, KI, RbI, and CsI) and tetrapropylammonium iodide (Pr₄NI). All the electrolytes based on binary salts have shown conductivity enhancement compared to their single cation counterparts. When combined with Pr₄NI, each of the Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺ cation containing iodide salts incorporated in the gel electrolytes has shown a room temperature conductivity enhancement of 85.59, 12.03, 12.71, 20.77, and 15.36%, respectively. The conductivities of gel electrolytes containing binary iodide systems with Pr₄NI and KI/RbI/CsI are higher and have shown values of 3.28, 3.43, and 3.23 mS cm⁻¹, respectively at room temperature. The influence of the nature of counterions on the performance of quasi-solid state dye-sensitized solar cells is investigated by assembling two series of cells. All the binary cationic solar cells have shown more or less enhancements of open circuit voltage, short circuit current density, fill factor, and efficiency compared to their single cation counterparts. This work highlights the importance of employing binary cations (a large and a small) in electrolytes intended for quasi-solid state solar cells. The percentage of energy conversion efficiency enhancement shown for the PECSCs made with electrolytes containing Pr₄NI along with Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺ iodides is 260.27, 133.65, 65.27, 25.32, and 8.36%, respectively. The highest efficiency of 4.93% is shown by the solar cell containing KI and Pr₄NI. However, the highest enhancements of ionic conductivity as well as the energy conversion efficiency were exhibited by the PECSC made with Li⁺-containing binary cationic electrolyte.

     

Preparation, properties, and crystal structures of organometallic ionic liquids comprising 1-ferrocenyl-3-alkylimidazolium-based salts of bis(trifluoromethanesulfonyl)amide and hexafluorophosphate

Bis(trifluoromethanesulfonyl)amide (TFSA), hexafluorophosphate (PF(6)(-)), and iodide salts of 1-ferrocenyl-3-alkylimidazolium were prepared and their thermal and physical properties, including the dependence on alkyl chain length (methyl-hexadecyl), were investigated. The TFSA salts were highly viscous ionic liquids with melting points around room temperature. 1-Ferrocenyl-4-methyltriazolium salts were also prepared for comparison. The ferrocenylimidazolium and ferrocenyltriazolium cations showed redox waves for both the ferrocenyl moiety and the azolium moiety and exhibited corresponding charge-transfer bands at around 330 nm, which were analyzed using the Marcus-Hush model. Crystal structure determinations at low temperature revealed that the PF(6) and iodide salts form layerlike structures composed of ionic layers of the charged moieties. The TFSA salt exhibited short hydrogen-bond-like intermolecular contacts between the hydrogen atoms of the cation and oxygen atoms of the anion.     

A view and a review of the melting of alkali metal halide crystals

Summary A representational model, proposed to account for the physical changes that accompany the melting of alkali halides, was described in Part 1 [1]. The liquid is portrayed as undergoing continual dynamic structural reorganization of its constituent ions between individual small domains, zones of various regular, crystal-type arrays. These alternative arrangements are stabilized by the enthalpy of melting, which, in liquids, relaxes the restriction for solids that only the single, most stable, crystal structure can be present. The dynamic character of the melt accounts for its fluid character and the loss of long-range order [1, 2]. This model is extended here to consider the phase diagrams of binary, common ion, alkali halide mixtures comprehensively reviewed in [3]. Factors determining whether each of these yields a eutectic, or a solid solution, on cooling are discussed and several trends in the 70-phase diagrams are identified. Eutectic formation, involving maintenance of the liquid state below the melting points of the pure components, is ascribed to the participation, in an extended dynamic equilibrium, of additional domains having the regular structures characteristic of double salts. The known crystalline double binary halides [3], Li/Cs or Rb/F, Cl, Br or I, melt at temperatures well below those of the simpler pure component salts. It is concluded that the set/liq model for melting, proposed in [1, 2], accounts for some important properties of the phase diagrams presented in [3].     

Ionic liquid crystal as a hole transport layer of dye-sensitized solar cells

Use of a new ionic liquid crystal, 1-dodecyl-3-methylimidazolium iodide, and iodine as an electrolyte of dye-sensitized solar cells leads to a high short circuit photocurrent density and a high light-to-electricity conversion efficiency, due to a self-assembled structure of the imidazolium cations, resulting in high conductivity of the electrolyte.     

Designing ionic liquids with boron cluster anions: alkylpyridinium and imidazolium [nido-C(2)B(9)H(11)] and [closo-CB(11)H(12)] carborane salts

A range of new alkylpyridinium and imidazolium carborane salts with [nido-C(2)B(9)H(12)](-), [closo-CB(11)H(12)](-), and [RC(2)B(11)H(11)](-) (R = methyl or butyl) anions have been prepared and characterized by physical and thermal methods, including the solid state structures of five of the salts determined by single crystal X-ray diffraction. The tendency of the salts to form low-melting ionic liquids has been assessed; all the salts studied with [nido-C(2)B(9)H(12)](-) anions melted below 100 degrees C and, significantly, have melting points that are 25-85 degrees C lower than those of the corresponding [closo-CB(11)H(12)](-) analogs, demonstrating that a wider range of boron-rich ionic liquid materials can be readily accessed.     

Stable mesoscopic dye-sensitized solar cells based on tetracyanoborate ionic liquid electrolyte

A stable dye-sensitized solar cell has been obtained based on a new binary ionic liquid electrolyte system containing 1-propyl-3-methylimidazolium iodide and 1-ethyl-3-methylimidazolium tetracyanoborate.     

Synthesis of some novel tetraimidazolium salts derived from diphenyl- and dimethylglycolurils

Several new tetrabromo compounds based on diphenyl- and dimethylglycolurils were synthesized. Sequential treatment of these compounds with imidazole, methyl iodide, and sodium tetrafluoroborate gave their corresponding tetra imidazolium salts. Some of these compounds because of their low melting points can be registered as a potential and new class of ionic liquids. Correspondence: Mehdi Bakavoli, Department of Chemistry, School of Sciences, Ferdowsi University, Mashhad 91375-1436, Iran.     

Revealing long-range density fluctuations in dialkylimidazolium chloride ionic liquids by dynamic light scattering

In this study, the structures and dynamics of ionic liquids of 1-allyl-3-methylimidazolium chloride ([AMIM][Cl]) and 1-n-butyl-3-methylimidazolium chloride ([BMIM][Cl]) were studied by dynamic light scattering with polarized and depolarized geometries in the temperature range from 300 to 400 K. The temperature range covered supercooled and liquid states for [BMIM][Cl] and covered the liquid state for [AMIM][Cl]. The results show that for these ionic liquids at all chosen temperatures only one ultraslow relaxation is observed in the polarized component of dynamic light scattering, however, the ultraslow relaxation is not observed in the depolarized component. The ultraslow relaxation exhibited several typical features of the "cluster" mode generally found in glass-forming liquids and polymer melts, such as diffusive, strongly scattering-vector-dependent, and nearly exponential characters, which thus corresponded to long-range density fluctuations. The physical origin for long-range density fluctuations was the existence of heterogeneities with large characteristic length scales in these ionic liquids. It was further considered that molecules of these ionic liquids not only tended to aggregate to form dynamic clusters but also possibly formed dynamic networks in the supercooled state and the heterogeneities could exist even at temperatures higher than the melting points.     

An iodine-free electrolyte based on ionic liquid polymers for all-solid-state dye-sensitized solar cells

An ionic liquid polymer, poly (1-alkyl-3-(acryloyloxy)hexylimidazolium iodide), was employed as an iodine-free electrolyte in all-solid-state dye-sensitized solar cells with an overall conversion efficiency of 5.29% under AM 1.5 simulated solar light (100 mW cm(-2)) illumination.     

Synthesis and characterization of ionic liquids incorporating the nitrile functionality

A series of imidazolium salts with the nitrile functional group attached to the alkyl side chain, viz. [CnCNmim][X] (where CnCNmim is the 1-alkylnitrile-3-methylimidazolium cation and Cn= (CH2)(n), n = 1-4; X = Cl, PF(6), and BF(4)) and [C3CNdmim][X] (where CnCNdmim is the 1-alkylnitrile-2,3-dimethylimidazolium cation and C(n) = (CH2)(n), n = 3; X = Cl, PF(6), and BF(4)), have been prepared and characterized using spectroscopic methods. The majority of the nitrile-functionalized imidazolium salts can be classed as ionic liquids since they melt below 100 degrees C. Four of the imidazolium salts have been characterized in the solid state using single-crystal X-ray diffraction analysis to reveal an extensive series of hydrogen bonds between H atoms on the cation and the anion. The relationship between the solid-state structure and the melting point is discussed. Key physical properties (density, viscosity, and solubility in common solvents) of the low melting ionic liquid have been determined and are compared with those of the related 1-alkyl-3-methylimidazolium and 1-alkyl-2,3-dimethylimidazolium ionic liquids. It was envisaged that these ionic liquids could act as both solvent and ligand for catalyzed reactions, and this application is demonstrated in hydrogenation reactions, which show that retention of the catalyst in the ionic liquid during product extraction is extremely high.     

Thermal characterization of solar salts from north of Chile and variations of their properties over time at high temperature

The current study has conducted a wide-ranging characterization, under high-temperature conditions, of a new ternary and quaternary heat transfer fluid, with the addition of Ca(NO₃)₂ and LiNO₃, two of the solar salt additives with a greater potential for being included in these new formulations proposed for the new generation of concentrated solar power (CSP) plants. In this direction, the present research is focused on viscosity and thermal stability since these salts try to increase the work temperature range in CSP plants. Viscosity tests were analyzed each 10 °C from 130 to 300 °C in order to check the variation in this parameter close to their melting points. Isothermal analysis at 450 and 500 °C was also performed through thermal gravimetric (TG) analysis, measuring any resulting loss of mass in the sample at these temperatures. Results were compared with the behavior in binary solar salt. These tests showed a progressive thermal degradation of salts over the time and the maximum temperature for operation in CSP has been corrected regarding the use of ternary and quaternary molten salts.     

New chiral ionic liquids based on imidazolinium salts

The preparation and application of a new series of chiral ionic liquids are described. The salts are based on imidazolinium cations. Some of the cations also incorporated an axial chirality at the C(2) position next to the central chirality. These cations display a very high rotational barrier along the arene–imidazolinium axis. Furthermore, an analogue with a chiral anion was prepared. The salts have low melting points. Their potential as solvents and as chiral shift reagents was explored, resulting for the first time in an example of a chiral ionic liquid as a shift reagent for a neutral compound.     

Thermal behaviour and electrochemical properties of bis(trifluoromethanesulfonyl)amide and dodecatungstosilicate viologen dimers

We report the synthesis and characterization of dimeric viologen salts (1',1'-(alkane-1,n-diyl)bis(1-ethyl-4,4'-bipyridinium) with n = 4-10) with bis(trifluoromethanesulfonyl)amide (bistriflimide, Tf(2)N(-)) as a counteranion. For n = 4, 5 and 6, and for the nonylviologen cation (1,1'-dinonyl-4,4'-bipyridinium) we also prepared salts with the totally inorganic dodecatungstosilicate anion, SiW(12)O(40)(4-), featuring a poly-charged surface and nanosized dimensions. The materials have been characterized by means of calorimetric techniques, X-ray diffraction and solid state NMR and a comparison is made with analogous monomeric viologen salts exhibiting smectic mesophases. A strong odd-even effect is observed in the melting points and in the thermal behaviour of the bistriflimide dimeric systems, similar to what was reported for dipolar calamitic liquid crystal dimers, although the studied viologen dimers are not mesomorphic. By increasing the size of the counteranion we have observed a destabilization of the crystal phases and of the mesophases in favour of a glassy amorphous state. Implications on the design of novel ionic liquid crystals are discussed. The electrochemical behaviour in solution has been investigated by cyclic voltammetry measurements: interestingly, the odd-even effect is clearly visible also in the redox potentials. The spin-pairing of the viologen radical cations formed at each end of the dimer is responsible for the observed redox trend. Insights on the structure of the spin-paired dimer have been obtained by DFT calculations.     

1-甲基-3-己基咪唑碘的合成及在染料敏化太阳电池中的应用

利用高压釜使1-甲基咪唑和碘代正己烷直接反应生成离子液体1-甲基-3-己基咪唑碘, 并考察了温度对反应的影响. 结果表明, 升高反应温度, 可使1-甲基咪唑和碘代正己烷按化学计量比进行反应, 产率近100%, 该方法操作简单, 所得产品纯度高, 反应过程不需要使用有机溶剂, 且对环境友好. 同时还测量了I-3在1-甲基-3-己基咪唑碘和1-甲基咪唑混合液中的表观扩散系数及其所组成的染料敏化太阳电池的光伏性能.     

High efficiency dye-sensitized nanocrystalline solar cells based on ionic liquid polymer gel electrolyte

An ionic liquid polymer gel containing 1-methyl-3-propylimidazolium iodide (MPII) and poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) has been employed as quasi-solid-state electrolyte in dye-sensitized nanocrystalline TiO2 solar cells with an overall conversion efficiency of 5.3% at AM 1.5 illumination.