Anion Pair Research Articles

Development of ionic liquid ion source with porous emitter for surface modification

Ionic liquid (IL) ion sources with three different emitter tip materials, stainless steel, tungsten and graphite were developed and examined on ion beam characteristics with respect to its ILs wettability. It was observed that EMIM-BF4 ion beam produces mostly single cations or anions for positive or negative modes respectively, and exhibits a few cation–anion pairs attached with a cation or an anion. On the other hand, the main content of the BMIM-PF6 ion beam was the cation–anion pairs while the single ions were minor components. As a result of ion current measurements, the largest and the most stable emission current were obtained for the graphite emitter tip. The results indicate that the emitter wettability plays an important role in the current stability.

Irradiation of ionic liquid ion beams on silicon and glass substrates

Irradiation of an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) ion beam on borosilicate glass and single crystalline Si(100) surface was demonstrated by using an ionic liquid ion source we developed. Surface smoothing on the glass substrates was produced by the irradiations at an acceleration voltage of 4kV with both positive and negative ion beams, which include cation–anion pairs attached to a single ion of either polarity. Water contact angle measurements and X-ray photoelectron spectroscopy indicated that the surface smoothing was probably caused by surface modification involving nano-ordered chemical etching by Si–F reaction, implantation and deposition of P, N and C.

Di‐ and Tetranuclear Complexes of Bis‐Tetradentate Pyrimidine‐Based Ligands with All‐Methylene‐ Versus Mixed Methylene/Ethylene‐Linked Arms

Eleven dinuclear and six tetranuclear complexes of two bis-tetradentate ligands, 4,6-bis[N,N-bis(2???-pyridylmethyl)aminomethyl]-2-phenylpyrimidine (LMe) and 4,6-[(2???-pyridylmethyl)(2???-pyridylethyl)aminomethyl]-2-phenylpyrimidine (LMix), have been prepared through reactions of ligand and metal salt in a ratio of 1:2 in MeCN or MeOH: FeII2LMe(H2O)4(MeCN)2(BF4)4 (1), FeII2LMix(H2O)4(BF4)4 (2), [CoII2LMe(H2O)(MeCN)](BF4)4??3/2H2O (3), [CoII2LMix(H2O)(MeCN)3](BF4)4??2H2O (4), [NiII2LMe(H2O)4](BF4)4??H2O (5), [NiII2LMix(H2O)3(MeCN)](BF4)4 (6), CuII2LMe(H2O)(MeCN)(BF4)4 (7), [CuII2Mix(MeCN)2(BF4)4] (8), [ZnII2LMe(H2O)(MeCN)3(BF4)4] (9), [ZnII2LMix(MeCN)3(H2O)(BF4)4] (10), [ZnII2LMe(H2O)2L(MeCN)2](ClO4)4 (11), FeII2FeIII2(LMe)2F4(BF4)6??1/2H2O (12), FeII4(LMix)2F4(BF4)4??5H2O (13), CoII2CoIII2(LMe)2F4(BF4)6 (14), [CoII4(LMix)2F4](BF4)4??3H2O (15), [NiII4(LMe)2F4](BF4)4 (16) and NiII4(LMix)2F4(BF4)4??8H2O (17). Dinuclear complexes were obtained from the reactions conducted in MeCN, whereas tetranuclear complexes resulted from reactions performed in MeOH. Five dimetallic (3??????6??? and 9???) and one tetrametallic complex (15???) were structurally characterized: the ligands are bis-tetradentate and the metal centres are bridged through the pyrimidine ring. In the tetrametallic 15???, two such dimetallic fragments are bridged by two pairs of fluoride anions. Variable-temperature magnetic susceptibility measurements and Heisenberg fitting of dinuclear 1???8 and tetranuclear 13???15 in all cases revealed weak intramolecular anti-ferromagnetic exchange coupling between the high-spin metal centres. A rigorous spin???orbit and exchange analysis was also performed on the dicobalt(II) complex 4. The dicopper(II) complexes 7 and 8 underwent a two-electron quasi-reversible reduction (CuII2 ??? CuI2), in both cases at a more negative potential (7: Em = ???0.18 V; 8: Em = ???0.19 V vs. 0.01 M AgNO3/Ag) than the analogous LEt (all-ethylene-armed ligand) complex (Em = +0.11 V vs. 0.01 M AgNO3/Ag), consistent with LMe and LMix being better able to stabilize copper(II) than LEt.

Effect of salts on the Co-fermentation of glucose and xylose by a genetically engineered strain of Saccharomyces cerevisiae

BackgroundA challenge currently facing the cellulosic biofuel industry is the efficient fermentation of both C5 and C6 sugars in the presence of inhibitors. To overcome this challenge, microorganisms that are capable of mixed-sugar fermentation need to be further developed for increased inhibitor tolerance. However, this requires an understanding of the physiological impact of inhibitors on the microorganism. This paper investigates the effect of salts on Saccharomyces cerevisiae 424A(LNH-ST), a yeast strain capable of effectively co-fermenting glucose and xylose.ResultsIn this study, we show that salts can be significant inhibitors of S. cerevisiae. All 6 pairs of anions (chloride and sulfate) and cations (sodium, potassium, and ammonium) tested resulted in reduced cell growth rate, glucose consumption rate, and ethanol production rate. In addition, the data showed that the xylose consumption is more strongly affected by salts than glucose consumption at all concentrations. At a NaCl concentration of 0.5M, the xylose consumption rate was reduced by 64.5% compared to the control. A metabolomics study found a shift in metabolism to increased glycerol production during xylose fermentation when salt was present, which was confirmed by an increase in extracellular glycerol titers by 4 fold. There were significant differences between the different cations. The salts with potassium cations were the least inhibitory. Surprisingly, although salts of sulfate produced twice the concentration of cations as compared to salts of chloride, the degree of inhibition was the same with one exception. Potassium salts of sulfate were less inhibitory than potassium paired with chloride, suggesting that chloride is more inhibitory than sulfate.ConclusionsWhen developing microorganisms and processes for cellulosic ethanol production, it is important to consider salt concentrations as it has a significant negative impact on yeast performance, especially with regards to xylose fermentation.

Towards molecular dynamics simulations of chiral room-temperature ionic liquids

We developed an all-atom non-polarizable force field for simulations of two chiral room-temperature ionic liquids (RTILs) derived from 1-n-butyl-3-methylimidazolium bromide ([bmim][Br]); namely, (R)-1-butyl-3-(3-hydroxy-2-methylpropyl)imidazolium bromide (hydroxypropyl) and 1-butyl-3-[(1R)-nopyl]imidazolium bromide (nopyl). The force field adopts the CHARMM parameters for intramolecular and repulsion–dispersion interactions, and it employs reduced partial atomic charges of the ions which we derived by quantum-mechanical calculations. The atomic charges of a cation are first assigned by the ChelpG method to yield the integer net charge +e. The ChelpG charges of the cation are then uniformly scaled down by a factor equal to the absolute value of a charge on the bromine anion obtained by the QTAIM method for the cation–anion pair. The net charges of the ions are around ±0.8e, which mimics the anion to cation charge transfer and many-body effects. Molecular dynamics (MD) simulations are used to estimate the bulk density and heat of vaporization of the RTILs at 300K and 1bar. MD simulations in the slab geometry combined with the intrinsic interface analysis are then employed to compare the vapor–liquid interface of the chiral RTILs with the interface of [bmim][Br] at 300K. We focus on the structural properties of the interfaces by computing the density profiles and surface roughness. The chiral RTILs are currently tested for separation of racemic mixtures of α-pinenes and the simulations complement experimental characterization of the chiral RTILs.

Bis[μ-1,3-bis(diphenylphosphanyl)propane-κ2P:P′]digold(I) tetrachloridonickelate(II) diethyl ether monosolvate

The title compound, [Au2(C27H26P2)2][NiCl4]·C4H10O, consists of a digold(I) complex cation, an [NiCl4]2− complex anion and a diethyl ether solvent mol­ecule. Two 1,3-bis­(di­phenyl­phosphan­yl)propane (dppp) ligands bridge two AuI atoms, forming a metallacycle in which each of the AuI atoms is coordinated in a slightly distorted linear environment by two P atoms. In the complex anion, the NiII atom is coordinated by four chloride ligands in a distorted tetra­hedral geometry. The complex cation and the complex anion form a cation–anion pair through two Au⋯Cl contacts of 3.040 (1) and 3.021 (2) Å. One of the phenyl groups of the dppp ligand is disordered over two positions with equal occupancies.

(S)-α-Benzylproliniumcis-[(S)-α-benzylprolinato]dichloridopalladium(II)

The title complex salt, (C12H16NO2)[PdCl2(C12H14NO2)], is of inter­est with respect to organic and organometallic catalysis. The compound crystallizes as very small orange–red irregular prisms and the asymmetric unit contains three crystallographically distinct cation–anion pairs. The coordination geometry about the palladium atoms is square-planar with the chloride ligands cis to one another. The structure displays N—H⋯Cl and O—H⋯O hydrogen bonding such that the N—H⋯Cl hydrogen bonds align the cation–anion pairs in a linear fashion along [001], with the O—H⋯O hydrogen bonds connecting these linear strands along [100] and [010].

Zn2(VO4)(IO3): A Novel Polar Zinc(II) Vanadium(V) Iodate with a Large SHG Response

The synthesis, crystal and electronic structures, and optical properties of the first zinc(II) vanadium(V) iodate, namely, Zn2(VO4)(IO3), are reported. Zn2(VO4)(IO3) crystallizes in the noncentrosymmetric (NCS) and polar space group Pc (No. 7) with a = 5.2714(8) Å, b = 10.0402(11) Å, c = 5.5070(8) Å, β = 101.326(10)°, and Z = 2. It displays a novel three-dimensional (3D) network structure composed of ZnO5, ZnO6, VO4, and IO3 polyhedra. One-dimensional (1D) chains of edge-sharing ZnO5 polyhedra and 1D chains of corner-sharing ZnO6 octahedra along the c-axis are interconnected via corner-sharing into a two-dimensional (2D) zinc oxide layer, and such layers are bridged by both VO4 tetrahedra and IO3 groups into a 3D network. The polarity in the structure is imparted by the alignment of the stereochemically active lone pairs of the iodate anions along the c-axis. The second harmonics generation (SHG) measurements on powder samples of Zn2(VO4)(IO3) under 1064-nm laser radiation revealed a large response of ∼6 × KDP, which is Type I phase-matchable. Thermal stability and optical properties, as well as theoretical calculations based on DFT methods, were also performed.

Chiral Brønsted acid-catalyzed enantioselective ionic [2+4] cycloadditions

The first asymmetric chiral N-triflylphosphoramide-catalyzed ionic [2+4] cycloaddition reaction of unsaturated acetals is described. This reaction proceeds through the intermediacy of a vinyl oxocarbenium/chiral anion pair, and the chiral N-triflylphosphoramide anion controls the stereoselectivity of the cycloaddition step. Moderate enantioselectivities (up to 80:20 e.r.) have been obtained when α,β-unsaturated dioxolanes were employed as the dienophiles. These reactions demonstrate strong dependence on the counterion coordinating properties and solvent polarity, a behavior characteristic of oxocarbenium ions.

Elucidating Interactions Between Ionic Liquids and Polycyclic Aromatic Hydrocarbons by Quantum Chemical Calculations

Using quantum mechanical calculations performed at the density functional level of theory, the present study explores the binding energetics, orbital energies, and charge transfer behavior accompanying sorption of 12 different ionic liquids (ILs) onto 6 archetypal polyaromatic hydrocarbons (PAHs). The ILs were based on combinations of three different onium cations (i.e., 1-butyl-3-methylimidazolium, 1-butylpyridinium, 1-butyl-1-methylpyrrolidinium) paired with four common anions, that is, bromide, tetrafluoroborate, hexafluorophosphate, and bis(trifluoromethylsulfonyl)imide. In general, the size of the anion as well as interaction of the butyl side chain present on the cation with the paired anion exerted significant influence over the cation ring orientation with respect to the PAH surface. A smaller highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy band gap was observed for pyridinium-based ILs upon adsorption on the PAH surface in comparison to imidazolium and py...

DFT Study of the Geometrical and Electronic Structures of Geminal Dicationic Ionic Liquids 1,3‐Bis[3‐methylimidazolium‐1‐yl]hexane Halides

AbstractIn this work, the geometrical and electronic properties of the mono cationic ionic liquid 1‐hexyl‐3‐methylimidazolium halides ([C6(mim)]+_X−, X=Cl, Br and I) and dicationic ionic liquid 1,3‐bis[3‐methylimidazolium‐1‐yl]hexane halides ([C6(mim)2X2], X=Cl, Br and I) were studied using the density functional theory (DFT). The most stable conformer of these two types ionic liquids (IL) are determined and compared with each other. Results show that in the most stable conformers, in both monocationic ILs and dicationic ILs, the Cl− and Br− anions prefer to locate almost in the plane of the imidazolium ring whereas the I− anion prefers nearly vertical location respect to the imidazolium ring plan. Comparison of hydrogen bonding and ionic interactions in these two types of ionic liquids reveals that these ionic liquids can be formed hydrogen bond by Cl− and Br− anion. The calculated thermodynamic functions show that the interaction of cation — anion pair in the dicationic ionic liquids are more than monocationic ionic liquids and these interactions decrease with increasing the halide anion atomic weight.

4-(4-Nitrobenzyl)pyridinium 3-carboxy-4-hydroxybenzenesulfonate

In the title salt, C12H11N2O2 +·C7H5O6S−, the dihedral angle between the benzene and pyridine rings in the 4-(4-nitro­benz­yl)pyridinium cation is 82.7 (2)°. Within the anion there is an intramolecular hydroxy-O—H⋯O(carboxylic acid) bond. In the crystal, the cation forms a single N+—H⋯Osulfonate hydrogen bond with the anion. These cation–anion pairs inter­act through duplex anion carb­oxy­lic acid O—H⋯Osulfonate hydrogen bonds, giving a centrosymmetric cyclic association [graph set R 2 2(16)]. The crystals studied were non-merohedrally twinned.

Temperature dependent resonant X-ray diffraction of single-crystalline Ge2Sb2Te5

The element distribution in the crystal structure of the stable phase of the well-known phase-change material Ge2Sb2Te5 was determined at temperatures up to 471 °C using single crystals synthesized by chemical transport reactions. Because of the similar electron count of Sb and Te, the scattering contrast was enhanced by resonant diffraction using synchrotron radiation (beamline ID11, ESRF). A simultaneous refinement on data measured at the K-absorption edges of Sb and Te as well as at additional wavelengths off the absorption edges yielded reliable occupancy factors of each element on each position (a = 4.2257(2) A, c = 17.2809(18) A, Pm1, R1 (overall) = 0.037). The dispersion correction terms Δf′ were refined and match experimental ones obtained from fluorescence spectra by the Kramers–Kronig transform. The structure contains distorted rocksalt-type blocks of nine alternating cation and anion layers, respectively, which are separated by van der Waals gaps between Te atom layers. Ge atoms prefer the cation positions near the center of the rocksalt-type block (occupancy factors Ge0.60(4)Sb0.36(2)), Sb atoms the one near the van der Waals gap (Ge0.33(7)Sb0.66(4)). Anti-site disorder is not significant. During heating up to 471 °C and subsequent cooling, a reversible structural distortion was observed. The refinements show that with increasing temperature the first pair of anion and cation layers next to the van der Waals gap becomes slightly detached from the block and increasingly resembles a GeTe-type layer. Thus, the difference between interatomic distances in the 3 + 3 cation coordination sphere of the mixed Ge–Sb position next to the gap becomes more pronounced. The element distribution, in contrast, neither changes during the heating experiment nor upon long-time annealing. Thus, the behavior of 9P-Ge2Sb2Te5 single crystals is predominantly under thermodynamic control.

Imidazolium salts and their polymeric materials for biological applications

Imidazolium salts, distinct from their parent imidazoles, are made up of a discrete cation and anion pair, and have found widespread utility as ionic liquids. A lesser known function of such imidazolium salts includes the application of these salts in biological systems, and several areas of bio-applications, including antitumour, antimicrobial, antioxidant and bioengineering applications, will be presented and discussed in this review. The wide-ranging applications and versatility of these imidazolium salts stem from the ease of their structural variation, in which properties such as amphiphilicity, lipophilicity and solubility can be tuned.

Crystal structures of Mosher's salt and ester elucidated by X-ray crystallography

The crystal structure of Mosher's salt 3, prepared from (R)-3,3,3-trifluoro-2-methoxy-2-phenylpropanoic acid [(R)-MTPA, (R)-1] and (R)-1-phenylethylamine [(R)-PEA, (R)-2], was determined using X-ray crystallography. In crystalline salt 3, the bifurcated hydrogen bond (i.e., the methoxy-group-assisted salt bridge) and the aromatic C–H⋯π interaction formed the closest ion pair of the MTPA anion and PEA cation. The crystal packing of salt 3 was also determined. The conformations of the crystalline (Racid)-MTPA esters were then statistically examined using the Cambridge Structural Database (CSD). For secondary alcohols, ca. 65% of the dihedral angles between the ester carbonyl groups and the trifluoromethyl groups ranged between −30° and 0°. The other conformational properties associated with the trifluoromethyl, methoxy, and phenyl groups were examined in detail. The conformation of the MTPA ester prepared from the tertiary alcohol is also discussed in this paper.

Two distinct tetranuclear motifs, rectangular vs. extended, are observed for complexes of a bis-tetradentate pyrimidine-based ligand

The 1 : 2 reactions of 4,6-bis[N,N-bis(2′-pyridylmethyl)aminomethyl]-2-phenylpyrimidine (LMe) and MnII, CoII, NiII and CuII chloride salts in MeOH gave the tetranuclear complexes [MnII4(LMe)2Cl8]·2H2O (1), CoII4(LMe)2Cl8·10H2O (2), [Ni4II(LMe)2Cl4]Cl4·8H2O (3) and [CuII4(LMe)2Cl6]Cl2·8H2O (4), respectively. X-ray crystal structure determinations carried out on three of the complexes revealed that in the case of NiII (3′) the LMe ligand is bound in the expected bis-tetradentate fashion, bridging the encapsulated pair of NiII centers via the pyrimidine ring, and that two pairs of chloride anions bridge a pair of such dimetallic units, affording a closed rectangular tetranuclear core overall. In contrast, in the case of MnII (1′) and CuII (4′) only one binding pocket of the LMe ligand strand binds in the expected tetradentate manner, whilst the other binds in a terdentate manner as one pyrimidine nitrogen atom does not bind, so in these cases the pyrimidine moiety does not bridge the metal centres, resulting instead in ‘extended’, linear tetranuclear assemblies.

The Reaction of 1,2-Dichloro-4,5-dinitrobenzene with Hydroxide Ion: Roles of Meisenheimer Complexes and Radical Pairs

The reaction of 1,2-dichloro-4,5-dinitrobenzene (DCDNB) with aqueous OH- produces (after acidification) 2-nitro-4,5-dichlorophenol with loss of NO2. Nevertheless, with > 2 mol L-1 OH-, only DCDNB was recovered due to the formation of the long-lived 3,6-dihydroxy Meisenheimer complex (M2-), and that in acid, reverted to the starting material. Fast formation of monohydroxy Meisenheimer complex (M1-) can be followed in DMSO:H2O 7:3 v/v and rate constants for its interconversion with DCDNB and for formation and return with M2- complex were estimated, with evidence for these reactions in DMSO:H2O 1:1 v/v and H2O. The rapid hydrogen exchange in OD- /D2O limits the use of1 H nuclear magnetic resonance (NMR) spectroscopy in identifying intermediates. 1 H and13 C NMR signals of M2- complex were observed in DMSO-H2O-KOH. There is evidence for the formation of free radicals in DMSO:H2O 4:1 v/v, and overall kinetics in more aqueous medium were treated in terms of the transient existence of anionic radical pairs.

Structures of N,N’-bis(tert-Butyl)-N-Formylethylenediamine Halides obtained by Salt Metathesis from Metal Precursors

N,N’-bis(tert-butyl)-N-formylethylenediamine iodide 1 and N,N’-bis(tert-butyl)-N-formylethylenediamine chloride 2 were obtained in an attempt to synthesize N-heterocyclic carbene iron(II) complexes via the free carbene route. In the process of generating the free carbenes for subsequent coordination to the iron(II) centres, 1 and 2 were isolated as products of imidazolinium salt hydrolysis. The iron(II) precursor salts were non-innocent in these reactions as the amine salts bear counter-anions of metathesis from the respective precursors used in each case, CpFe(CO)2I for 1 and FeCl2 for 2. Compounds 1 and 2 were characterized by single crystal diffraction analysis, 1H and 13C NMR, IR spectroscopy and HRMS. The single crystal X-ray diffraction results reveal that compound 1 crystallizes in the orthorhombic P2(1)2(1)2(1) space group while compound 2 crystallizes in the triclinic P-1 space group. In compound 1, the molecules are packed with the cations related through a centre of inversion about a pair of iodide anions while in 2 the smaller chloride counter anions are sandwiched between the cations. The interionic distance is shorter in compound 2 at 2.26 A as compared to 2.59 A in compound 1. An attempted synthesis of N-heterocyclic carbene iron(II) complexes via the free carbene route resulted in the isolation of N,N’-bis(tert-butyl)-N-formylethylenediamine iodide and N,N’-bis(tert-butyl)-N-formylethylenediamine chloride as hydrolysis products incorporating anions from the corresponding iron(II) metal precursors.

4-(Bromomethyl)benzyl]triphenylphosphonium bromide acetonitrile monosolvate

In the title compound, C26H23BrP+·Br−·C2H3N, the dihedral angles between the plane of the benzylic phenyl ring attached to the P atom and the planes of the three directly attached phenyl rings are 34.04 (12), 45.48 (13) and 87.18 (9)°. In the crystal, centrosymmetric pairs of cations and anions are linked into dimeric aggregates via C—H⋯Br hydrogen bonds. There is also a C—H⋯N hydrogen bond to the acetonitrile solvent mol­ecule.

Extraction of cadmium bromide and picrate by 18-crown-6 ether into various less-polar diluents: Analysis of overall extraction equilibria based on their component equilibria with formation of their ion pairs in water

Extraction constants (Kex and Kex±) of CdBr2 into eleven diluents and Cd (Pic)2 into eight diluents by 18-crown-6 ether (18C6) and apparent distribution constants (KD,A) of pairing anions (A−) were determined at 25°C. Here, Kex, Kex±, and KD,A were defined as [CdLA2]o/[Cd2+][L]o[A−]2, [CdLA+]o[A−]o/[Cd2+][L]o[A−]2, and [A−]o/[A−], respectively; L=18C6, A−=Br− and picrate ion (Pic−), and the subscript “o” denotes the diluent phase. Also, K2org was estimated from the ratio Kex/Kex±. Using the two extraction constants and their component equilibrium ones, extraction-abilities and -selectivities of the diluents for the above extraction systems were discussed. From the KD,A values, the distribution constants of cationic ion-pairs CdLA+ into 1,2-dichloroethane (DCE) and dichloromethane (DCM) were also standardized and thereby ion-transfer potentials of CdLA+ at water (w)/DCE and w/DCM interfaces were estimated. Further, interactions of neutral ion-pairs CdLA2 with w molecules were examined with cohesive energy densities obtained from the plots of log Kex,ipversus log KD,L, where Kex,ip and KD,L denote an ion-pair extraction constant of CdLA2 into the diluents and the distribution one of 18C6, respectively.