Pyridinium Cations Research Articles

Chiral Poly(ionic liquid) with Nonconjugated Backbone as a Fluorescent Enantioselective Sensor for Phenylalaninol and Tryptophan.

Here, a novel fluorescent chiral poly(ionic liquid) ( S)-PCIL-4 with nonconjugated backbone is designed and synthesized in the control of micelle through free-radical polymerization, whose fluorescence emission maximum is at λem,max = 430 nm. It is observed that polymers with spatially proximate units (phenyl group and pyridinium cation) have photoluminescence through spatial π-π and ion-π interaction. Then, ( S)-PCIL-4 can be served as a fluorescent turn off/on sensor for chiral recognition of phenylalaninol and tryptophan in the presence of Cu(II). For example, when ( S)-PCIL-4-Cu(II) is treated with ( R/ S)-phenylalaninol, it will exhibit different fluorescence responses. Values of the enantiomeric fluorescence difference ratio for phenylalaninol and tryptophan are 1.10 and 1.08, respectively. In brief, we believe that the approach opens up a possible pathway to prepare a variety of fluorescent polymers with nonconjugated backbone and proves to be desirable in further application.

A polyoxometalate gel electrolyte with enhanced electrochemical performance

A novel hybrid gel electrolyte has been synthesized by self-assembling of 1-(3-sulfonic group) propyl pyridine (PyPS) cation and the heteropoly anion. The results of FTIR spectra and XRD patterns indicate the synthesized hybrid gel electrolyte [PyPS]5SiMo[Formula: see text]VO[Formula: see text] possesses lamellar structure with [Formula: see text]-spacing of 2.09[Formula: see text]nm. The electrochemical stability potential window is up to 3[Formula: see text]V. Ionic conductivity of [Formula: see text][Formula: see text]S[Formula: see text]cm[Formula: see text] was observed above the phase transformation temperature under ambient condition. The conductivity enhances with increasing temperatures.

Majority‐Rules Effect and Allostery in Molecular Recognition of Calix[4]arene‐Based Triple‐Stranded Metallohelicates

The triple-stranded metallohelicates 1 a,/1 b-3 a/3 b possessing internal guest binding cavities surrounded by calix[4]arene units were synthesized through coordination-driven self-assembly. UV/Vis titration experiments verified that the metallohelicates encapsulated N-methyl pyridinium cations bearing amino acid groups to form host-guest complexes. The guest chirality was transferred to the helicity of the helicates through the steric contact between the stereogenic center of the amino acid group and the metal cores. The (M) helicity was induced when guests the (R)-4--(R)-6 were accommodated within the cavities. The multiple guest complexation within the self-assembled helicates 2 a and 3 a displayed large positive cooperative effects, indicating that the first guest complexation preorganizes the rest of the cavities to facilitate a subsequent guest binding. This cooperativity results in the majority-rules effect in the chiral guest binding for 2 a and 3 a.

A New Family of Heterometallic LnIII[12-MCFeIIIN(shi)-4] Complexes: Syntheses, Structures and Magnetic Properties

A new family of LnIII [12-Metallacrown-4] compounds of formulas (C5H6N) [LnFe4(shi)4(C6H5COO)4(Py)4]·3.5Py [Ln = EuIII (1); GdIII (2); TbIII (3); DyIII (4); and, H3shi = salicylhydroxamic acid] were obtained through one-pot reactions with H3shi, Fe(NO3)3·9H2O, and, Ln(NO3)3·6H2O as reagents. Single-crystal X-ray analyses show that they are isostructural and have the similar [12-MCFeIII N(shi)-4] core, with four benzoate molecules bridging the central LnIII ion to the ring FeIII ions. The negative charge of the 12-MC-4 metallacrown is balanced by one pyridinium cation, which forms the hydrogen bond with an adjacent solvent pyridine molecule. Magnetic measurements demonstrate antiferromagnetic coupling interactions and field-induced slow magnetic relaxation in complex 4.

Recycling of Polysilicon Byproduct SiCl4 Dissolved in Ionic Liquids

Silicon tetrachloride (SiCl4) is one of the primary by-products products of the polysilicon industries, which must also be handled with care, as it is both toxic and reactive. The dissolution of SiCl4 and electrodeposited of Si in ionic liquids (ILs) was investigated. Six kinds of ILs were examined as the solvents; the cations were 1-Butyl-3-methylimidazolium 1-butyl-3-methylimidazolium ([Bmim]+), 1-Hexyl-3-methylimidazolium ([Hmim]+), 1-Octyl-3-methylimidazolium ([Omim]+), N-butyl-3-methylpyridinium ([B3MePy]+), N-hexyl-3-methylpyridinium ([H3MePy]+), N-octyl-3-methylpyridinium ([O3MePy]+); the anion was bis[(trifluoromethyl)sulfonyl]imide ([NTf2]−). The results indicated that a decrease in the solubility of SiCl4 in ILs followed an increase in temperature. The presence of Si-O bonding between the ionic liquid and SiCl4 enhanced the SiCl4 dissolving capacity of in the ILs with anion of [NTf2]−. Longer alkyl chain lengths in the imidazolium and pyridinium cations of the ILs exhibited a better performance in dissolving SiCl4, due to the presence of C-Cl and C-Si formed between the ILs and SiCl4. Si was electrodeposited on a Ti plate under potential of 2.92V, of which a Si weight of up to 28.43 wt% was observed. The deposition product on the electrode is in the coexistence state of Si and SiOx due to the deposition conditions at ordinary temperature and pressure.

Synthesis, Characterization, and Physicochemical Properties of Hydrophobic Pyridinium‐based Ionic Liquids with N‐Propyl and N‐Isopropyl

Synthesis and physicochemical properties of four pyridinium‐based ionic liquids (ILs), N‐propylpyridinium bromide [N‐propylPyr]+[Br]–, N‐isopropylpyridinium bromide [N‐isopropylPyr]+[Br]–, N‐propylpyridinium hexafluorophosphate [N‐propylPyr]+[PF6]–, and N‐isopropylpyridinium hexafluorophosphate [N‐isopropylPyr]+[PF6]– are reported. The molecular structures of these compounds were characterized by FT‐IR, 1H, 19F, and 31P NMR, spectroscopy. The thermal properties, conductivity, and solubility of these ionic liquids were also investigated. The effects of propyl and isopropyl alkyl lateral chain at the N‐position of pyridinium cation on the thermal stability, conductivity, and solubility of ionic liquids are discussed. The results obtained confirmed that the ionic liquids based on pyridinium cations exhibit higher decomposition temperature, low melting points, immiscible with water, and their conductivities are mainly influenced by mobility of ions.

Two tris(oxalato)ferrate(III) hybrid salts with pyridinium derivative isomers as counter cations: synthesis, crystal structures, thermal analyses, and magnetic properties

Two organic–inorganic hybrid salts, tris(2-amino-4,6-dimethylpyridinium) tris(oxalato)ferrate(III), (C7H11N2)3[Fe(C2O4)3] (1), and tris(4-dimethylaminopyridinium) tris(oxalato)ferrate(III) tetrahydrate, (C7H11N2)3[Fe(C2O4)3]·4H2O (2), have been synthesized and characterized by elemental and thermal analyses, IR spectroscopy, single-crystal X-ray diffraction, and SQUID magnetometry. Compounds 1 and 2 crystallize in triclinic P-1 and monoclinic C2/c space groups, respectively. Each compound contains the anionic complex [Fe(C2O4)3]3- in which the central metal is six-coordinate in a slightly distorted octahedron defined by three chelating oxalate(2-) ligands. The two substituted pyridinium cations are isomers. However, due to the great steric hindrance provided by the bulky cation, 2-amino-4,6-dimethylpyridinium, only the 4-dimethylaminopyridinium cation, the smallest of this series, led to formation of 2 with enough vacant spaces to be occupied by four solvent water molecules. In the crystals, cations and anions are connected via hydrogen-bonds of the types N–H⋯O in 1 and N–H⋯O and O–H⋯O in 2, with π–π stacking interactions between the pyridine rings stabilizing the 3-D framework. The thermal studies confirmed the anhydrous character of salt 1 and the presence of water molecules in salt 2. The magnetic susceptibility measurements in the 2–300 K temperature range revealed weak antiferromagnetic coupling in the two salts.

Antimicrobial evaluation and action mechanism of pyridinium-decorated 1,4-pentadien-3-one derivatives

A type of pyridinium-decorated 1,4-pentadien-3-one derivatives possessing flexible alkyls were designed and synthesized by integrating the key scaffolds of pyridinium cations and 1,4-pentadien-3-one skeleton in a single molecular architecture. Antimicrobial bioassays indicated that some of the target molecules exerted considerable bioactivities against six phytopathogenic strains, especially for Xanthomonas oryzae pv. oryzae, the minimal EC50 value can reach to 0.504 µg/mL. A plausible action mechanism for this kind of compounds was proposed and confirmed by employing fluorescent spectroscopy, fluorescence microscopy, and scanning electron microscopy. We anticipated that this finding can promote high-efficient lead compounds discovery in the research of antimicrobial chemotherapy.

XeO3 adducts of pyridine, 4-dimethylaminopyridine, and their pyridinium salts

Xenon trioxide (XeO3), a highly shock-sensitive detonator, forms adducts with the N-bases, pyridine and 4-dimethylaminopyridine (4-DMAP). The reactions of pyridine and 4-DMAP with XeO3 in rigorously dried CH3CN and in CH3CN that had not been dried yielded (C5H5N)3XeO3(1) and (4-(CH3)2NC5H5N)3 XeO3·H2O (3), respectively, whereas their reactions in HF-acidified CH3CN yielded [C5H5NH]4[HF2]2[F]2(XeO3)2(2) and [4-(CH3)2NC5H4NH][HF2]XeO3(4). Crystalline (1), (2), and (4) failed to detonate when subjected to mechanical shock; however, (3) was significantly more sensitive to mechanical or thermal shock than XeO3. The adducts and their pyridinium salts were structurally characterized by low-temperature, single-crystal X-ray diffraction, and Raman spectroscopy. The crystal structures of (1) and (3) consist of XeO3 molecules that are N-coordinated to three pyridine and 4-DMAP ligands, respectively. A water molecule is also H-bonded to two oxygen atoms of two adjacent XeO3 molecules of (3). The pyridinium cations of (2) and (4) are H-bonded to [F]− and/or [HF2]− ions which are, in turn, F-coordinated to XeO3. Both [F]− ions of (2) bridge two XeO3 molecules to form Xe2F2-rings. Each [HF2]− anion of (4) bridges two cations and two XeO3 molecules by means of Xe⋯F secondary bonds and N(H)⋯F H-bonds. Quantum-chemical calculations for (1) and (2) provided energy-minimized geometries and calculated vibrational frequencies and intensities which were used to aid in the assignments of their Raman spectra. The NBO analyses showed the Xe⋯N, Xe⋯O, and Xe⋯F secondary bonding interactions are electrostatic in nature and may be described as σ-hole bonds.

High pressure phase behaviour of carbon dioxide and two ionic liquids based on a benzyl functionalized cation

The high pressure phase behaviour of a CO2 and 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [BzMeIM][NTf2], binary system was experimentally measured at high pressure up to about 13.5 MPa and at a temperatures range of 293.2–323.2 K. The solubilities were determined by measuring the bubble point pressure of the binary mixture comprising CO2 and an ionic liquid using a phase equilibrium apparatus including a high pressure variable-view cell. The effect of a benzyl functional group in different cations, imidazolium and pyridinium, on the high pressure phase behaviour of the CO2 and 1-benzylpyridinium bis(trifluoromethylsulfonyl)imide, [BzPY][NTf2], binary system was also investigated within similar temperature and CO2 mole fractions ranges. The experimental data correlated well with the Peng-Robinson equation of state. In general, higher CO2 solubilities were obtained in [BzPY][NTf2] than those in [BzMeIM][NTf2] at similar temperature and pressure. This may be attributed to the difference in aromaticity in pyridinium and imidazolium cations.

Synthesis, Characterization, and Computational Modeling of N-(1-Ethoxyvinyl)pyridinium Triflates, an Unusual Class of Pyridinium Salts.

N-Substituted pyridinium salts constitute one of the most valuable reagent classes in organic synthesis, due to their versatility and ease of use. Herein we report a preliminary synthesis and detailed structural analysis of several N-(1-ethoxyvinyl)pyridinium triflates, an unusual class of pyridinium salts with potentially broad use as a reagent in organic synthesis. Treatment of pyridines with trifluoromethane sulfonic acid and ethoxyacetylene generates stable, isolable adducts which have been extensively characterized, due to their novelty. Three-dimensional structural stability is perpetuated by an array of C–H•••O hydrogen bonds involving oxygen atoms from the –SO3 groups of the triflate anion, and hydrogen atoms from the aromatic ring and vinyl group of the pyridinium cation. Predictions from density functional theory calculations of the energy landscape for rotation about the exocyclic C–N bond of 2-chloro-1-(1-ethoxyvinyl)pyridine-1-ium trifluoromethanesulfonate (7) and 1-(1-ethoxyvinyl)pyridine-1-ium trifluoromethanesulfonate (16) are also reported. Notably, the predicted global energy minimum of 7 was nearly identical to that found within the crystal structure.

Synthesis of Stable Salts Containing the Hydridophosphate Anion [P(C2F5)3F2H]–

The reaction of the industrial product (C2F5)3PF2 with LiAlH4 in THF solution selectively furnished the hydridophosphate anion [P(C2F5)3F2H]–. The compound [PPh4][P(C2F5)3F2H] is obtained as a colorless solid on a multigram scale by salt metathesis in aqueous THF. Combining [P(C2F5)3F2H]– with various imidazolium and pyridinium cations affords ionic liquids with melting points well below room temperature. (C2F5)3PF2 also abstracts hydrides from amines, affording the hydridophosphate anion [P(C2F5)3F2H]– and the corresponding imminium cations which add a second amine moiety by intra‐ or intermolecular adduct formation.

Pyridinium-Functionalized Pyromellitic Diimides with Stabilized Radical Anion States.

In this work, we report the stabilization of the reduced states of pyromellitic diimide by charge-balancing the imide radical anions with cationic pyridinium groups attached to the aromatic core. This structural modification is confirmed by single-crystal X-ray diffraction analysis. Characterization by (spectro)electrochemical experiments and computations reveal that the addition of cationic groups to an already electron-deficient ring system results in up to +0.57 V shifts in reduction potentials, largely as a consequence of charge screening and lowest unoccupied molecular orbital-lowering effects. This formal charge-balancing approach to stabilizing the reduced states of electron-deficient pyromellitic diimides will facilitate their incorporation into spin-based optoelectronic materials and devices.

Crystal structures of bis-[4-(di-methyl-amino)-pyridinium] tetra-kis-(thio-cyanato-κN)manganate(II) and tris-[4-(di-methyl-amino)-pyridinium] penta-kis(thio-cyanato-κN)manganate(II).

The crystal structures of the title salts, (C7H11N2)2[Mn(NCS)4] (1) and (C7H11N2)3[Mn(NCS)5] (2), consist of manganese(II) cations that are tetra-hedrally (1) or trigonal-bipyramidally (2) coordinated to four or five terminal N-bonded thio-cyanate ligands, respectively, into discrete anionic complexes. The negative charge is compensated by two (1) or three (2) 4-(di-methyl-amino)-pyridinium cations, which are protonated at the pyridine N atom. The asymmetric unit of compound 1 consists of one anionic complex and two 4-(di-methyl-amino)-pyridinium cations, whereas that of compound 2 consists of two anionic complexes and six 4-(di-methyl-amino)-pyridinium cations, all of them located in general positions. These complexes are linked by N-H⋯S, C-H⋯S and C-H⋯N hydrogen-bonding inter-actions between the 4-(di-methyl-amino)-pyridinium cations and the thio-cyanate ligands into three-dimensional network structures.

Pyridinium lead tribromide and pyridinium lead triiodide: quasi-one-dimensional perovskites with an optically active aromatic π-system.

Two novel hybrid organic-inorganic perovskites, pyridinium lead tribromide and pyridinium lead triiodide, are prepared. Based on the XRD data, we find that the compounds are quasi-one-dimensional crystals of Pna21 symmetry. DFT calculations demonstrate that the valence band of the new compounds is comprised of the occupied p-orbitals of the halogen anions, while their conduction bands CB and CB + 1 are composed mainly of the unoccupied π-orbitals of the aromatic pyridinium rings. The computed DOS matches well with the recorded XPS spectra. The pyridinium lead tribromide and pyridinium lead triiodide absorption peaks derived from the experimental DRS are located at ∼3.1 eV and ∼2.4 eV, respectively. An agreement between the experimentally and theoretically predicted absorption spectra is found. The synthesized compounds extend the range of quasi-one-dimensional organometallic perovskites suitable for optical and possibly electronic applications.

Fragment and cluster ions from gaseous and condensed pyridine produced under electron impact.

We report on direct measurement of all major ion-fragments and cluster-ions formed during high-energy electron impact of 2 keV on gaseous and condensed-phase pyridine. The ion-fragments of the parent pyridine cation are discussed in groups according to the number of atoms from the aromatic ring. The ion yield distributions within these groups show significant shifts towards higher masses for condensed pyridine compared to gaseous pyridine due to hydrogen migration. A wide spectrum of desorbed hydrogenated fragment-ions and ionic clusters with masses up to 320 u are observed for pyridine. The ion yields for the protonated parent molecule (C5H5NH+), the dehydrogenated dimer (C10H9N2+) and the dehydrogenated trimer (C15H12N3+) depend on the mass of the desorbing ionic clusters. The strongest cluster signals are assigned to binding between the parent cation and subunits of the pyridine molecule. Quantum-chemical calculations reveal that the formation of a bond between the pyridine molecules and a carbenium ion is crucial for the stability of selected cluster ions.

Solid-State Esterification via Ionic-to-Covalent Bond Transformation in Ionic Molecular Crystals Consisting of Disubstituted Anthracene Anion-Cation Combinations

Abstract Thermal solid-state reactions involving ionic-to-covalent bond transformation were achieved in the ionic molecular crystals of 1,8-bis[(pyridin-1-ium-1-yl)methyl]anthracene anthracene-1,8-dicarboxylate to produce the cyclic diester. The crystal structure given by X-ray diffraction analysis showed that the electrostatic interaction between the benzyl pyridinium cation and the carboxylate anion successfully works to locate these reaction sites close to each other and that there are channels for crystalline solvents and the liberated pyridine to escape. Thereby, the cyclic diester was selectively formed by the crystal-to-crystal reaction, which was proven by powder XRD profiles and optical microscopic and SEM images of the crystals before and after the reaction. This is the first thermal crystal-to-crystal condensation reaction. Another ionic molecular crystal of 1,8-bis[(pyridin-1-ium-1-yl)methyl]anthracene anthraquinone-1,8-dicarboxylate was also studied. Therein, the corresponding cyclic diester was also obtained, but the crystals were transformed to amorphous solid by the reaction.

N-Heterocycle-Ligated Borocations as Highly Tunable Carbon Lewis Acids.

The relative (to BEt3) hydride ion affinity (HIA) of a series of acridine borenium salts has been calculated, with some HIAs found to be similar to that for [Ph3C]+. The HIA at the acridine C9 position is controlled by both acridine and the boron substituents, the latter presumably affecting the strength of the B=N bond in the acridane-BY2 products from hydride transfer. Through a range of hydride abstraction benchmarking reactions against organic hydride donors the experimental HIA of [F5acr-BCat]+ (cat = catechol, F5acr = 1,2,3,4,7-pentafluoroacridine) has been confirmed to be extremely high and closely comparable to that of [Ph3C]+. The high HIA of [F5acr-BCat]+ enables H2 and alkene activation in a FLP with 2,6-di-tert-butylpyridine. Finally, the HIA of pyridine and quinoline borenium cations has been determined, with the HIA at boron in [PinB(amine)]+ (pin = pinacol, amine = pyridine or quinoline) found to be relatively low. This enabled the hydroboration of pyridine and quinoline by HBPin to be achieved through the addition of 5–10 mol % of bench-stable cationic carbon Lewis acids such as 2-phenyl-N,N-dimethylimidazolium salts.

Electrochemical Behavior of Pyridinium and N-Methyl Pyridinium Cations in Aqueous Electrolytes for CO2 Reduction.

The electrochemical reduction of aqueous pyridinium and N-methyl pyridinium ions is investigated in the absence and presence of CO2 and electrolysis reaction products on glassy carbon, Au, and Pt electrodes are studied. Unlike pyridinium, N-methyl pyridinium is not electroactive at the Pt electrode. The electrochemical reduction of the two pyridine derivatives was found to be irreversible on glassy carbon. These results confirmed the essential role of the N-H bond of the pyridinium cation. In contrast, the electrochemical response of N-methyl pyridinium ion at the glassy carbon electrode suggests that a specific interaction occurs between the glassy carbon surface and the aromatic ring of the pyridinium derivative. For all electrodes, an enhancement of current was observed in the presence of CO2 . However, NMR spectroscopy of the solutions following electrolysis showed no formation of methanol or other possible byproducts of the reduction of CO2 in the presence of either pyridinium derivative ion.

New pyridinium based ionic dyes for the hydrogen evolution reaction

The presented work comprised the synthesis and characterization of new ionic organic dyes as potential photosensitizer (PS) in the photocatalytic H2 evolution reaction. The presented dyes are consisting of donor-π-acceptor (D-π-A) structures that are commonly used for organic dyes for organic solar cells. The acceptor is based on a cationic pyridinium moiety. Furthermore, a complex was synthesized, in which a D-π-A photosensitizer is linked as ligand to cobaloxime. The latter is a common proton reduction catalyst. The attached ligand enabled a fast intramolecular electron transfer to the cobalt center. The resulted complex showed high stability and potential in the homogeneous photocatalytic H2 evolution reaction. Finally, one ionic dye showed a high activity when combined with TiO2 and Pt in a heterogeneous hydrogen evolution reactions with a TOF of up to 407 h−1.