Series Of Cations Research Articles

Non-planarity in four-membered homo-cyclic compounds A4 (A = O, S, Se, Te, Po) and restoring their planarity: a study of the pseudo-Jahn–Teller effect

The bent D2d structures of the four-membered homo-cyclic compounds A4 (A = O, S, Se, Te, Po) were examined computationally to understand the pseudo-Jahn–Teller effect (PJTE). To do this, ab initio geometry optimizations and corresponding frequency calculations (at the MP2/cc-pVQZ-(PP) level of theory) show that all A4 compounds under-consideration are unstable in their planar (D4h) configuration. The ground state and six low-lying non-degenerate and degenerate electronic excited states were computed at the CASSCF (6,7)/cc-pVQZ-(PP) along the bending normal coordinate connecting the D4h and D2d geometries; these represent the adiabatic potential energy surfaces (APESs). Based on the APESs, the coupling between the ground state (1A1g) and the 1B2u excited state is demonstrated to be the reason for the planar structure bends from the high-symmetry D4h geometry into the lower-symmetry D2d stable equilibrium configuration. The solution to the PJTE (1A1g + 1B2u) ⊗ b2u problem is useful to answer the question of “how instability rises in A4 planar configuration?”. Although all A4 compounds in the series are non-planar with D4h symmetry, but geometrical optimizations and frequency calculations show that coordination of two noble gas cations (NG+ = He+, Ne+ and Ar+) above and below the σh plane of the A4 (A = O, S, Se) ring could restore ring planarity in (A4 NG)2+ complexes. The PJTE is also quenched in the A42+ (A = O, S, Se, Te, Po) cation and dication series, and planarity of the rings is also restored, i.e., the high-symmetry D4h structure becomes the equilibrium configuration.

Mesoporous anion-cation-codoped Co9S8 nanorings for enhanced electrocatalytic oxygen evolution reactions

Recently, the design and synthesis of Co9S8 micro/nanostructures have attracted attention as electrochemical energy storage and conversion devices due to their low cost and environmental friendliness. Herein, Co9S8 nanorings were synthesized via a one-step solvothermal method with the incorporation of Fe ions, subsequently, properly selenized to boost their electrocatalytic performance. The morphology and structure of the series of cation and anion regulated Co9S8 nanorings were characterized, the electrochemical oxygen evolution reaction (OER) properties were assessed. It is worth noting that the as-prepared catalysts, especially the innovative Fe and Se ions double doped Co9S8 nanorings, denoted as Se/Fe-Co9S8-0.14, exhibited good electrocatalytic OER performance with low overpotential (298 mV) and high durability under alkaline conditions. This work provides a new perspective to develop non-noble metal Co9S8-based OER electrocatalysts with a superior electrocatalytic performance.

Exploring enthalpies of formation of imidazolium-, pyridinium-, and pyrrolidinium-based ionic liquids with dicyanamide anion using quantum chemical methods

Abstract In this work, quantum chemical calculations have been performed on the ionic liquids based on imidazolium, pyridinium, and pyrrolidinium cations with the dicyanamide anion. The dispersion-corrected B3LYP exchange-correlation functional was used to optimize geometries. Enthalpies of formation were calculated at the high-level G3(MP2) theory by employing both the atomization energy and reaction enthalpy approaches. There exists a very good agreement between the predicted enthalpies of formation and available experimental values. For the first time, the enthalpies of formation have been predicted for 21 ion pairs with no available experimental data. The calculated enthalpies of formation are decreased with increasing alkyl chain length. Linear correlations were observed between enthalpy of formation and number of carbon atoms in the alkyl side-chain for all of the studied series of cations. Regardless of the cation type, the contribution of each CH2 group in the alkyl chain to the enthalpy of formation was also determined.

Ion Pair Structures and Hydrogen Bonding in RnNH4-n Alkylammonium Ionic Liquids with Hydrogen Sulfate and Mesylate Anions by DFT Computations.

Density function theory calculations are employed to study the interaction of amines bearing different numbers of alkyl substituents of different sizes on the nitrogen atom with sulfuric and methanesulfonic acids. The proton affinities of the studied amines are calculated, and it is shown that the higher the value is, the more probable is its protonation. The most stable structures of the ion pairs resulting from the acid-base interaction are obtained and characterized. The geometric parameters of the ion pairs and the characteristics derived from the NBO and QTAIM analysis show that there are hydrogen bonding interactions between the cation and the anion. The hydrogen bonding character of the ion pairs and the strength of the interaction between the ions strongly depend on the nature of the cation itself. The interaction between the ions in the ion pairs weakens with the increase in the cation size. The trend of change in the structural parameters of the H-bonds and energetic characteristics in the cation series for the studied ion pairs is not dependent on the nature of the anion.

Tuning the luminescence properties of Mn4+‐activated CaYAlO4 phosphor by co‐doping cations for indoor plant cultivation

AbstractTo fulfil the demands of high‐power plant growth lamps, cation co‐doping is an effective way to tune the photoluminescence properties of manganese (Ⅳ)‐activated aluminate phosphors. Therefore, we managed to synthesize a series of cations co‐doped CaYAlO4:xMn4+, mSr2+, M+ (M+ = Li+, Na+, and K+) (CYAO:Mn, Sr, M) far‐red‐emitting phosphors. The excitation spectrum of these phosphors contained two excitation bands, and the opposite effects of these two bands on the luminescence intensity have been observed with the increase of Mn4+ concentration. By adding 0.1 mol Sr2+ ions to replace Ca2+ site, the emission intensity and thermal stability of CYAO:Mn phosphors can be enhanced. Furthermore, the luminescence properties of CSYAO:Mn can be further improved by co‐doping monovalent alkali metal ions to serve as charge compensators, the increased number of Mn4+ luminescence centers. Moreover, 0.6 mol% Na+ can increase the initial emission intensity of the phosphors by 117% as the best ratio. The characteristic emission spectrum of the phosphors CYAO:Mn,Sr,M correspond to the phytochrome PFR of plants. These experiments and characterization results have certified that these phosphors have a potential application in indoor plants cultivation.

Amplified spontaneous emission properties of solution processed CsPbBr3 perovskite thin films doped with large-group ammonium cations

Inorganic solution processed CsPbBr3 perovskite thin films are highly promising optoelectronic materials and have been applied in solar cells, light emitting diodes, and photodetectors. They show good electroluminescence properties combined with high thermal stability. In this work, CsPbBr3 perovskite thin films doped with a series of organic cations of various chain lengths, namely, methylammonium (MA), ethylammonium (EA), butylammonium (BA) and octylammonium (OA) at optimized molar ratios of (organic cations: Cs+), were fabricated with a two-step solution process. The crystalline structure, surface morphology and photophysical properties of the films were characterized in detail. The surface morphology of the films was improved with reduced surface roughness, accompanying by doping with the organic cations. The amplified spontaneous emissions (ASE) were observed from all of the different CsPbBr3 films at room temperature. The gain coefficients for the doped CsPbBr3 films were higher than the pristine films, due to much reduced bulk defects, reduced non-radiative recombination in the films, as well as improved surface quality of the films. This work provides a simple method of preparing organic cations modified CsPbBr3 laser gain media of high performance.

Routine, ensemble characterisation of electrophoretic mobility in high and saturated ionic dispersions

With the industrialisation of nanoparticle manufacture, the pervasive incursion of nanoparticles into the environment, the need to characterise nano-scale pharmaceuticals and living systems in replicated in vivo conditions, the continuing development of new theories to describe the electro-kinetic behaviour of nano-particles in representative ionic strengths and numerous other applications, there is an urgent requirement to provide simple and effective experimental tools to validate these models and explore new systems. Micro-electrophoresis implemented with a diffusion barrier, which isolates the dispersed phase from the electrode surface, is demonstrated as enabling such measurements for the first time, preventing the catastrophic outgassing, precipitation and sample degradation observed when the dispersed phase is in close proximity to the electrode surface. Using a measurement of a few minute’s duration in a standard laboratory light scattering instrument we reproduce the theoretically predicted phenomena of asymptotic, non-zero electrophoretic mobility with increasing ionic strength, the cationic Hofmeister series dependency, charge inversion and a continuously decreasing variation in mobility with pH as molarity increases. Standard operating procedures are developed and included to encourage further work.

Secondary structure effects on internal proton transfer in poly-peptides.

A pump–probe approach was designed to determine the internal proton transfer (PT) rate in a series of poly-peptide radical cations containing both histidine and tryptophan. The proton transfer is driven by the gas-phase basicity difference between residues. The fragmentation scheme indicates that the gas-phase basicity of histidine is lower than that of radical tryptophan so that histidine is always pulling the proton away from tryptophan. However, the proton transfer requires the two basic sites to be in close proximity, which is rate limited by the peptide conformational dynamics. PT rate measurements were used to probe and explore the peptide conformational dynamics in several poly-glycines/prolines/alanines. For small and unstructured peptides, the PT rate decreases with the size, as expected from a statistical point of view in a flat conformational space. Conversely, if structured conformations are accessible, the structural flexibility of the peptide is decreased. This slows down the occurrence of conformations favorable to proton transfer. A dramatic decrease in the PT rates was observed for peptides HAnW, when n changes from 5 to 6. This is attributed to the onset of a stable helix for n = 6. No such discontinuity is observed for poly-glycines or poly-prolines. In HAnW, the gas-phase basicity and helix propensity compete for the position of the charge. Interestingly, in this competition between PT and helix formation in HA6W, the energy gain associated with helix formation is large enough to slow down the PT beyond experimental time but does not ultimately prevail over the proton preference for histidine.

From Distortion to Disconnection: Linear Alkyl Diammonium Cations Tune Structure and Photoluminescence of Lead Bromide Perovskites

AbstractOrganic ammonium cations play a vital role in building structures and tuning energy bands of organic–inorganic halide perovskites and the consequent photoelectric characteristics. Here, two 2D lead bromide perovskites: flat‐layered (BDA)PbBr4 (BDA = 1, 4‐butanediammonium), corrugation‐layered (PDA)7Pb6Br26 (PDA = 1, 3‐propanediammonium) and a 1D nanobelt‐shaped (EDA)2PbBr6 (EDA = ethylenediammonium) are built to explore their tunable structure, energy bands, and photoluminescence by a series of linear alkyl diammonium cations. Significant “spatial effect” of diammonium cations directly controls the space configurations of these lead bromide perovskites. From 2D (100)‐flat to 1D (110)‐nanobelt, distortions and disconnections of lead bromide layers are beneficial to the quantum confinement and generation of self‐trapping exciton (STE) energy levels of low‐dimensional perovskites. Upon ultraviolet excitation, (BDA)PbBr4, (PDA)7Pb6Br26, and (EDA)2PbBr6 exhibit blue, broadband yellowish white, and “warm” white emissions, respectively. Density functional theory combining STE theory demonstrates their bandgap changes and emission mechanisms. This work provides a basis for tuning the structure of low‐dimensional organic–inorganic halide perovskites for better photochromic properties.

Effect of sodium salts on diffusion of poly(vinyl alcohol) in aqueous solutions

Abstract The Taylor dispersion technique has been used for measuring the tracer diffusion coefficients, D0Tracer, for poly (vinyl alcohol) (PVA) in aqueous systems containing two specific electrolytes (i.e., NaCl and Na2SO4) at three different concentrations (0.020, 0.050 and 0.10 mol dm−3), and at 25 °C. The selection of these salts has been based on the Hofmeister series of cations and anions, which order the ions with respect to the behavior of some macroscopic properties (such as, surface tension) and that can be interpreted as an effect salting-out or salting-in, depending if the target ions are strongly (kosmotropic) or a weakly hydrated (chaotropic). In this work, we have been used the combination of two kosmotropic ions (Na2SO4) and another one with a kosmotropic cation and a chaotropic anion (NaCl). These data, complemented by NMR measurements, permit us to have a better understanding about the effect of these sodium salts on transport and thermodynamic behaviour of PVA.

Molecular sieving of tetraalkylammonium cations on cation exchange systems in DC electric field

Ion exchange membranes and ion exchange resin particles are widely used in electro-membrane separation processes such as electrodeionization and electrodialysis. The internal structure of these ion exchange systems implicitly determines their properties, which, in turn, strongly affect the efficiency of the separation process. Here, we indirectly investigate the internal structure of a heterogeneous cation exchange membrane and cation exchange resin particles with the use of homologous series of tetraalkylammonium chlorides. The tetraalkylammonium cations form a series of cations of various sizes amendable for sieving on the studied systems. This series is used for determination of the cation of critical size. The performed experimental study focuses on investigating characteristic features of current-voltage curves measured for individual tetraalkylammonium chloride solutions and their effect on water splitting reaction and electroconvection. Our experimental data show that while tetramethyl-, tetraethyl-, and tetrapropylammonium cations can easily be exchanged by both the membranes and the resin particles, tetrapentyl- and tetrahexylammonium cations are poorly exchanged by both studied systems due to their size. Tetrabutylammonium cation, possessing the Stokes diameter of around 1 nm, turns out to be the cation with the critical size. We observe a strong effect of the counterion size on the occurrence of electroconvection that is pertinent to the overlimiting region of the ion exchange systems. While small counterions allow intensive electroconvection to develop, large counterions have a damping effect on the electroconvective motion. The measurement of the pH changes in our systems during chronoamperometric experiments indicates that water splitting takes place in none of them. Our results classify counterions into two groups based on their ability to pass through the investigated cation exchange systems. The first group includes counterions easily exchanged by the ion exchange system. The other group contains cations that cannot be exchanged due to their size. The counterions from the second group are possible foulants with increased potential for adsorption onto the cation exchange systems due to strong electrostatic attractions. Our technique can be used for the determination of critical sizes of other cation exchange systems.

Cation Engineering in Two-Dimensional Ruddlesden-Popper Lead Iodide Perovskites with Mixed Large A-Site Cations in the Cages.

The Goldschmidt tolerance factor in halide perovskites limits the number of cations that can enter their cages without destabilizing their overall structure. Here, we have explored the limits of this geometric factor and found that the ethylammonium (EA) cations which lie outside the tolerance factor range can still enter the cages of the 2D halide perovskites by stretching them. The new perovskites allow us to study how these large cations occupying the perovskite cages affect the structural, optical, and electronic properties. We report a series of cation engineered 2D Ruddlesden-Popper lead iodide perovskites (BA)2(EAxMA1-x)2Pb3I10 (x = 0-1, BA is n-butylammonium, MA is methylammonium) by the incorporation of a large EA cation in the cage. An analysis of the single-crystal structures reveals that the incorporation of EA in the cage significantly stretches Pb-I bonds, expands the cage, and induces a larger octahedral distortion in the inorganic framework. Spectroscopic and theoretical studies show that such structural deformation leads to a blue-shifted bandgap, sub-bandgap trap states with wider energetic distribution, and stronger photoluminescence quenching. These results enrich the family of 2D perovskites and provide new insights for understanding the structure-property relationship in perovskite materials.

Computational design of two-photon active organic molecules for infrared responsive materials

Aiming at proposing design rules, the mechanism of two-photon absorption is analyzed in a series of π-conjugated organic cations and their neutral precursors exhibiting aggregation-enhanced optical properties.

Specific and non-specific interactions between metal cations and zwitterionic alanine tripeptide in saline solutions reported by the symmetric carboxylate stretching and amide-II vibrations.

The "specific" interaction between metal cations (Na+, Ca2+, Mg2+, and Zn2+) and the charged COO- group, and the "non-specific" interaction between these cations and the peptide backbone of a zwitterionic trialanine (Ala3) in aqueous solutions were examined in detail, using linear infrared (IR) absorptions of the COO- symmetric stretching and the amide-II (mainly the C-N stretching) modes as IR probes. Different IR spectral changes in peak positions and intensities of the two IR probes clearly demonstrate their sensitivities to nearby cation distributions in distance and population. Quantum chemistry calculations and molecular dynamics simulations were used to describe the cation-peptide interaction picture. These combined results suggest that Na+ and Ca2+ tend to bind to the COO- group in the bidentate form, while Mg2+ and Zn2+ tend to bind to the COO- group in the pseudo-bridging form. The results also show that while all three divalent cations indirectly interact with the peptide backbone with large population, Ca2+ and Mg2+ can be sometimes distributed very close to the backbone. Such a non-specific cation interaction can be moderately sensed by the C-N stretching of the amide-II mode when cations approach the polar amide C[double bond, length as m-dash]O group, and is also influenced by the NH3+ charge group located at the N-terminus. The results suggest that the experimentally observed complication of the Hofmeister cation series shall be understood as a combined specific and non-specific cation-peptide interactions.

High-Voltage Resistant Ionic Liquids for Lithium-Ion Batteries.

With the growing demand for high energy and high power density rechargeable lithium-ion batteries, increasing research is focused on improving the output voltage of these batteries. Herein, a series of pyrrolidinium and piperidinium cations with various N-substituents (including cyanomethyl, benzyl, butyl, hexyl, and octyl groups) were synthesized and investigated with respect to their electrochemical stability under high voltages. The influence of substitutions at the N-position of pyrrolidinium and piperidinium cations on their high-voltage resistance was studied by both theoretical and experimental approaches. The voltage resistance was enhanced as the electron-donating ability of the substitutes increased. Furthermore, 1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([C6Py][TFSI]) exhibited the highest decomposition voltage at approximately 5.12 V and showed promising potential in a lithium-ion battery.

Formation of Al + (C 6 H 6 ) 13 : The Origin of Magic Number in Metal–Benzene Clusters Determined by the Nature of the Core

The identification of highly abundant, “magic” species in the mass spectra of clusters have proven to be valuable in nanoscience, leading to the discovery of new stable species such as fullerenes a...

Three‐component, one‐pot synthesis of pyrano[3,2‐c]chromene derivatives catalyzed by ammonium acetate: Synthesis, characterization, cation binding, and biological determination

AbstractThree‐component reaction of arylaldehydes with malononitrile and 4‐hydroxycoumarine using CH3COONH4 as a catalyst at reflux was used for the synthesis of novel substituted pyrano[3,2‐c]chromene derivatives. The structure of these compounds was assigned by spectroscopic data such as (IR, 1HNMR, 13CNMR, and mass spectral data). The cation binding properties of chromene derivatives 4a‐c towards Cu2+, Ni2+, and Zn2+ were studied in methanol. The results showed that Zn2+ is the most complexed in this series of cations, and 4c is best complexed with either Ni2+ and Zn2+. Antimicrobial properties of new pyrano[3,2‐c]chromene derivatives are investigated, the compound 4c presents against Micrococcus luteus LB 14110 an MIC value of 0.0185 mg/mL quite better to that of ampicillin (0.0195 mg/mL) used as standard. Concerning acetylcholinesterase inhibition activity (AChEI), compound 4c presents an interesting AChEI activity with an inhibition of 52%.

Rationally designed phenanthrene derivatized triazole as a dual chemosensor for fluoride and copper recognition.

A 1,2,3-triazole chemosensor containing phenanthrene and phenol moieties (PhTP) was efficiently synthesized via copper (I)-catalyzed azide-alkyne cycloaddition, "click chemistry". PhTP is a dual analyte sensor for fluoride and copper (II) ions in homogeneous medium. Deprotonation of the phenolic OH proton by the fluoride ion is responsible for a change in fluorescence color from blue (PhTP) to yellowish-orange (PhTP-fluoride adduct), while a charge transfer between the triazole nitrogen of the chemosensor and Cu2+ revealed a turn-off fluorescence output. The detection capability of PhTP was analyzed with a series of anions (F-, Cl-, Br-, I-, H2PO4-, ClO4-, OAc-, BF4-) and cations (Fe3+, Fe2+, Cu2+, Ag+, Cr3+, Al3+, Co2+, Ni2+, Cd2+, Zn2+). With anions, competitive fluorescence responses under UV lamp were observed for acetate and dihydrogen phosphate anions, but maximum response from fluoride ion was substantiated from steady state absorption and fluorescence experiments. With cations, PhTP displayed a selective and sensitive recognition towards Cu2+ ion through spectral modulation in absorption spectroscopy and a turn-off fluorescence response. Nuclear magnetic resonance (NMR) spectroscopic titration studies supported the results obtained through photophysical studies and provided evidence for the ion-binding sites on the probe.

Persistent peroxidase mimics of graphene oxide anchored cerium molybdate sensor: An effective colorimetric detection of S2− and Sn2+ ions

Environmental pollution involves contaminants, pollutants and toxic chemicals that create disturbance in natural environment and is one of the most serious threats for human health. This issue may be resolved by designing an efficient catalyst however it is challenging to design nontoxic catalyst to solve the environmental related issues. In this report we have developed a novel catalyst cerium molybdate (CeM) as a peroxidase mimic with cotyledons type morphology which is not reported yet. GO-cerium molybdate (GOCeM) nanostructures are also designed first time with enhanced performance as compare to bare CeM for colorimetric detection of dual ions (S2- and Sn2+). GOCeM nanostructures synthesized with ex-situ approach show high catalytic activity in comparison to pure CeM and GOCeM (in-situ) catalysts. The value of Michaelis-Menten constant (Km) and maximum initial velocity (Vmax) of pure CeM catalyst for TMB is found to be ~ 0.66 mM and 1.71 x 10–8 Ms-1 respectively. Km and Vmax value of GOCeM (in-situ and ex-situ) catalyst was found to be 0.39 mM, 1.78 x 10–8 Ms-1 and 0.30 mM, 2.5 x 10–8 Ms-1 respectively that is quite lesser than pure CeM catalyst. Km and Vmax value of GOCeM (ex-situ) catalyst for H2O2 was also calculated and found to be 0.44 mM and 3.3 x 10–8 Ms-1 respectively. The catalyst shows high sensitivity and selectivity of S2- and Sn2+ions among the series of cations and anions. The limit of detection (LOD) of S2- ions has been observed as 11.70 μΜ with the linearity range 20–100 μM, while the limit of detection of Sn2+ ions was observed as 5.58 μM with linearity range about 10 80 μΜ. The present work exhibits the high catalytic activity of GOCeM (ex-situ) catalyst in terms of good sensitivity and selectivity.

A Brønsted Acidic Ionic Liquid as an Efficient and Selective Catalyst System for Bioderived High Molecular Weight Poly(ethylene 2,5-furandicarboxylate).

Green synthesis of bioderived high-molecular-weight poly(ethylene 2,5-furandicarboxylate) (PEF) over metal-free catalysts is a significant challenge. This study focuses on PEF prepared from ethylene glycol and 2,5-furandicarboxylic acid (FDCA) through a direct esterification method with ecofriendly metal-free ionic liquids (ILs) as catalysts. The catalytic activities of a series of imidazolium cations in the presence of various anions are systematically investigated and found to be mainly governed by the anions. Among the ILs studied, 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2 MIM]BF4 ) is identified as the best catalyst, showing excellent catalytic activity, selectivity, and stability, even at low catalyst loadings (0.1 mol % w.r.t. FDCA). Optimization of the polymerization parameters enables [C2 MIM]BF4 -catalyzed production of PEF with a high number-average molecular weight (Mn =5.25×104 g mol-1 ). The relationship between Brønsted acidity and catalytic activity is also investigated and the results show that the trend in catalytic activity is in good agreement with that in Brønsted acidity, as determined by the Hammett method. Additionally, on the basis of experimental results and density functional theory calculations, an electrophilic activation mechanism induced by hydrogen bonds is proposed. This strategy of adjustable acidity and anion structure in ILs provides an opportunity to develop other ILs for bio-based polyesters through green synthesis pathways.