Polymeric Cation Research Articles

Ionization‐engineered two‐dimensional confined channels in GO membranes for highly efficient OH− separation

AbstractOH− sieving membranes provide a valuable means for treating alkaline effluents but their development presents several challenges. In this study, the concept of ionization engineering is applied to two‐dimensional (2D) laminated membranes to facilitate OH− separation. This concept is demonstrated through the stacking of the self‐designed sulfonated graphene oxide (SGO) nanosheets to fabricate 2D membranes. The SGO membranes enhance synergistically the OH− dialysis coefficients and separation factors when treating simulated NaOH/Na2WO4 alkaline wastewater, compared with the performance of 2D GO membranes and commonly adopted polymeric cation exchange membranes. Furthermore, the separation factor achieved by the SGO membranes is considerably higher than that of most of the existing alkali recovery membranes. Results of molecular dynamics simulations indicate that the high efficiency of OH− separation in the 2D SGO confined channels is attributable to dehydration effects and intensified electrostatic repulsion. Overall, this research provides an alternative strategy for achieving rapid OH− sieving through the ionization of 2D confined channels.

Light-Induced Polymeric Frustrated Radical Pairs as Building Blocks for Materials and Photocatalysts.

Polymeric frustrated Lewis pairs, or poly(FLP)s, have served to bridge the gap between functional polymer science and main group catalysis, pairing the uniqueness of sterically frustrated Lewis acids and bases with a polymer scaffold to create self-healing gels and recyclable catalysts. However, their utilization in radical chemistry is unprecedented. In this paper, we disclose the synthesis of polymeric frustrated radical pairs, or poly(FRP)s, by in situ photoinduction of FLP moieties, where their Lewis acidic and basic centers are tuned to promote single electron transfer (SET). Through systematic manipulation of the chemical structure, we demonstrate that inclusion of ortho-methyl groups on phosphine monomers is crucial to enable SET. The generation of radicals is evidenced by monitoring the stable polymeric phosphine radical cations via UV/vis and EPR spectroscopy. These new poly(FRP)s enable both catalytic hydrogenation and radical-mediated photocatalytic perfluoroalkylations. These polymeric radical systems open new avenues to design novel functional polymers for catalysis and photoelectrical chemistry.

The 1D‐Polymeric (Te72+)n in (Te7)[MF6]2 (M=As, Sb, Nb, Ta) by Solvothermal, Microwave Assisted, and Electrochemical Synthesis

AbstractReactions of tellurium with metal pentafluorides MF5 (M=As, Sb, Nb, Ta) in liquid SO2 under supercritical conditions at 160 °C yield (Te7)[MF6]2 containing the polymeric Zintl cation (Te72+)n consisting of chair‐shaped Te6 rings connected via single Te atoms. Crystal structure analyses show all four compounds to crystallize isotopically in the (Te7)[AsF6]2 structure type. Monitoring the reactions via Raman spectra reveal that (Te4)[MF6]2 is formed as an intermediate, which reacts with Te finally to (Te7)[MF6]2. Crystal structures of (Te4)[MF6]2 (M=Nb, Ta) were determined. Microwave assisted solvothermal synthesis give analogous results in very short reaction time. All compounds are also accessible via electrochemical oxidation of Te in presence of [MF6]− as electrolyte. (Te7)[AsF6]2 is a semiconductor with σ=10−7 S/cm at 300 K and an energy for the thermally activated electron process of 0.91 eV. Theoretical calculations on the self‐consistent hybrid DFT level confirm that the fundamental band gap is independent from the kind of M. The frontier orbitals are predominantly composed of Te states. Raman bands at 196, 178, 153, and 138 cm−1 are specific for (Te72+)n. Phonon calculations of (Te7)[TaF6]2 confirm three intensive Raman bands at 210, 174 and 163 cm−1. The corresponding normal modes are mainly localized on (Te7)n.

An oxalato-bridged dimetallic heptanuclear [K5IFe2III] complex anion with guanidinium as counter cation: Synthesis, crystal structure, Hirshfeld surface analysis and magnetism

An oxalato-bridged heterometallic heptanuclear [K5IFe2III] hybrid salt, (CH6N3)[K5(H2O)4Fe2(C2O4)6] (1) (CH6N3+ = guanidinium cation) has been synthesized and characterized by elemental and thermal analyses, IR spectroscopy, single-crystal X-ray diffraction, EPR and SQUID magnetometry. The asymmetric unit in 1 is composed of a dimetallic heptanuclear [K5(H2O)4Fe2(C2O4)6]− anionic complex and a guanidinium CH6N3+ cation insuring the charge compensation. Each Fe3+ center in the anionic complex is six-coordinate in a distorted octahedron defined by three chelating oxalato(2-) ligands. In contrast, the coordination numbers for K+ centers range from 7 to 9. The structural feature of focal interest in 1 is formation of an extended anionic network encapsulating guanidinium cations. This structure can be considered a sheet-MOF, where metal ions and oxalates (linkers) form infinite 2D units. The 3-D supramolecular architecture is stabilized by OH∙∙∙O and NH∙∙∙O hydrogen bonds linking polymeric oxalato-bridged anionic assemblies and organic cations. The thermal studies confirmed the anhydrous character of salt 1 and showed a three-step decomposition to yield a mixture of Fe2O3 and K2O as final residue. EPR spectrum of 1 is in accordance with the oxidation state + 3 of the iron center in an octahedral environment. Temperature-dependence susceptibility measurements investigated in the temperature range 2–300 K revealed weak antiferromagnetic coupling at low temperatures in salt 1. The distributions of different types of intermolecular interactions in the crystal structure were quantified by Hirshfeld surface analysis and their associated fingerprint plots.

Unraveling energy storage behavior of independent ions in carbon electrode for supercapacitors by polymeric ionic liquids and electrochemical quartz crystal microbalance

A fundamental understanding of the charge storage mechanism of electrochemical double-layer capacitors (EDLCs) requires an in-depth storage behavior investigation of independent ions (individual cations or anions) on the electrode surface. The direct in-situ observation for energy storage behavior of individual ions under realistic conditions remains challenge. Herein, in-situ monitoring the energy storage behavior of independent ions is realized with assistance of polymeric ionic liquids skillfully. Triangle cyclic voltammogram (CV) curves indicate that polymeric imidazole cations PVBIm+ with huge size cannot enter the active carbon pores upon charging, whereas only free anions can. The CV and electrochemical quartz crystal microbalance (EQCM) simultaneously detect ion adsorption/desorption during charging. It’s proposed that ion adsorption/desorption is governed by electrostatic attraction and repulsion of charged particles. PVBIm+ are adsorbed on the electrode surface due to ion adsorption mechanism during the negative polarization and have a small capacity contribution. Free anions contribute capacitance, their number entering the pore is determined by the interaction between polycaions and anions. Moreover, PVBIm(0.1)+ with higher polymerization degree may promote desorption of polycations and prevent further adsorption of anions at higher potential in positive polarization. This work not only observes the charging behavior of independent ions, but also reveals the relevant charging mechanism through EQCM, paving the way for panorama of EDLC.

A new heteroleptic cuprous polymer constructed by a cyanopyridine ligand exhibiting a supramolecular framework structure and luminescence.

Luminescent cuprous complexes are of great importance among coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The title heteroleptic cuprous polymer solvate, catena-poly[[[(9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane)-κ2P,P'](μ-pyridine-3-carbonitrile-κ2N1:N3)copper(I)] hexafluorophosphate dichloromethane trisolvate], {[Cu(C6H4N2)(C39H32OP2)]PF6·3CH2Cl2}n, conventionally abbreviated as {[Cu(3-PyCN)(Xantphos)]PF6·3CH2Cl2}n, where Xantphos and 3-PyCN represent (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane) and pyridine-3-carbonitrile, respectively, has been described. In this polymer solvate, the asymmetric unit consists of three dichloromethane solvent molecules, a hexafluorophosphate anion and a polymeric heteroleptic cuprous complex cation, in which the cuprous centre is in a CuP2N2 tetrahedral coordination and is coordinated by two P atoms from the Xantphos ligand and two N atoms from two 3-PyCN ligands (the pyridyl and cyano N atoms). It is through the connection of the μ2-bridging 3-PyCN ligand that these cuprous centres are linked into a one-dimensional helical chain structure. The chains are further assembled through C-H...π interactions to form a supramolecular metal-organic framework containing solvent-accessible channels. The UV-Vis absorption and photoluminescence properties of this heteroleptic cuprous polymer have been studied on as-synthesized samples. Its luminescence emission should mainly originate from the metal-to-ligand charge transfer excited state.

Synthesis of silicate and alumina pillared MWW zeolite as ethane dehydroaromatization catalyst

Pillared MWW zeolites were prepared with polymeric hydroxyl-aluminum Keggin-Al13 cations and tetraethylorthosilicate as pillaring agents to investigate catalyst acidity and interlayer structure impact on ethane dehydroaromatization. The intercalation effect of the pillars causes the MWW zeolite to be stretched between the layers, which cause the 12 member ring (MR) pocket structure to be exposed to outside surface. The modification method can effectively generate the micropore and mesopore MWW zeolite composite, MCM-36. The introduction of silica columns and alumina columns led to the overall decrease of acidity and the increase of weak and Lewis acid of pillared MWW zeolites, respectively. Although the strong Brönsted acid sites of MWW play major effect on catalyzing aromatization of ethylene generated by the dehydrogenation of ethane to aromatics, the modification decreases the cracking of ethylene oligomers. The 12-MR pockets exposed on the pillared MWW zeolite can provide more reaction sites for xylene generation.

Fluoride removal by hybrid cation exchanger impregnated with hydrated Al(III) oxide nanoparticles (HCIX-Al) with novel closed-loop recyclable regeneration system

A high concentrations of fluoride (F-) in groundwater limits drinking water supplies and results in fluorosis for hundreds of millions of people globally. A novel F- selective adsorbent (HCIX-Al) with a closed-loop regeneration system was developed, characterized, and assessed for its effectiveness in F- removal using both synthetic and natural groundwater. The system used an inexpensive polymeric macroporous cation exchanger doped with hydrous aluminum oxide (HAlO) nanoparticles. The HAlO nanoparticles were loaded into the matrix of the polymer phase by ion-exchange reactions between Al3+ and Ca2+ ions that bind with sulfonic acid functional groups of the cation exchangers. Hydrogen ions were generated in-situ during the HAlO formation process, creating acidic conditions inside the polymeric phase, which significantly increased F- sorption capacity (maximum sorption capacity = 5.75 mg/g at pH 7.5). While most other aluminum oxide-based F- selective sorbents suffer from low F- removal capacity at neutral to alkaline pH of typical groundwater, the HCIX-Al exhibited high F- sorption capacity even using alkaline (pH 8.5) groundwater. The treated water had a pH greater than 6.5 and non-detectable levels of aluminum (detection limit 0.002 mg/L), which complies with drinking water regulations. The HCIX-Al material can be reused by conditioning the exhausted material with a closed-loop regeneration chemical containing a recyclable 12% AlCl3 solution. The F- was precipitated from the regeneration system as CaF2 using lime at pH 11. This material, including a novel regeneration scheme, offered high F- removal capacity, cost-effectiveness, and provided a sustainable defluoridation process.

Polymeric Network of Amines and Metals Colloids: Conformational Analysis of Interaction, Orientation with DNA

Over the last decade numerous promising synthetic, non-viral gene delivery systems have been developed and an outline of their potential advantages and disadvantages has materialized [1]. Synthetic vectors have advantages in interconnected pharmaceutical issues, safety, and ease of use but tend to be less efficient than some viral systems. Advanced delivery systems can be developed that will have higher potential and more advantages. Moreover, physicochemical properties including charge, dissociation behavior, and the shape and nanoparticle size of the cationic complexes can play a significant role in efficient gene transfer in vitro and in vivo. Even though the interaction between the polymeric cations and DNA is electrostatic in origin, geometric and chemical structures of the polymer also play a substantial character in complex formation. Even the number of positive charges and the spacing of cationic charges within the polymer upsets the size of DNA nanoparticles fashioned by polycations [2]. Hence, a complete set of biophysical measurements for the characterization of physical and chemical properties of cationic complexes offered consists of cationic polymers/surfactants with DNA. By considering this beginning as a study on the structural properties of the cationic complexes, the understanding of the effect of polymer architecture on the DNA/cationic polymer interaction at the molecular level in terms of DNA stability, conformation, size, shape, binding affinity, and complete thermodynamics of the interaction are also necessarily required [3].

Interfacial nanostructure and friction of a polymeric ionic liquid-ionic liquid mixture as a function of potential at Au(1 1 1) electrode interface

HypothesisThe polymeric cations of polymeric ionic liquids (PILs) can adsorb from the bulk of a conventional ionic liquid (IL) to the Au(111) electrode interface and form a boundary layer. The interfacial properties of the PIL boundary layer may be tuned by potential. ExperimentsAtomic force microscopy has been used to investigate the changes of surface morphology, normal and lateral forces of a 5 wt% PIL/IL mixture as a function of potential. FindingsPolymeric cations adsorb strongly to Au(111) and form a polymeric cation-enriched boundary layer at −1.0 V. This boundary layer binds less strongly to the surface at open circuit potential (OCP) and weakly at + 1.0 V. The polymeric cation chains are compressed at −1.0 V and OCP owing to electrical attractions with the electrode surface, but fully stretched at + 1.0 V due to electrical repulsions. The lateral forces of the 5 wt% PIL/IL mixture at −1.0 V and OCP are higher than at + 1.0 V as the polymeric cation-enriched boundary layer is rougher and has stronger interactions with the AFM probe; at + 1.0 V, the lateral force is low and comparable to pure conventional IL due to displacement of polymeric cations with conventional anions in the boundary layer.

Novel synthesis of natural cation exchange resin by crosslinking the sodium alginate as a natural polymer with 1,6-hexamethylene diisocyanate in inert solvents: Characteristics and applications

Novel synthesis of natural polymeric cation exchanger from sodium alginate reagent as natural polymer (CAlg-Na)n has been developed. This procedure takes place by crosslinking the solid sodium alginate with 1,6-hexamethylene diisocyanate (HDI) in dryness benzene as inert solvent (DB). The experimental results for crosslinking the alginate using different degrees of crosslinking of HDI/DB (w/w) showed that the capacity of the synthesized resin for binding the polyvalent metal ions reached its maximum at 30% of (HDI/D) ratio. This work aims to present a novel synthesis of cation exchange resin from natural polymers as an alternative promising competitor of low-cost, high performance and non-toxicity for removal of the toxic heavy metal ions in wastewater remediation and radionuclide pollutants from environmental contaminated media. The results obtained from various applied techniques for determining the bounded metal ion concentrations with (CAlg-Na)n indicated that the resin capacity was followed the order U(VI) > Cu(II) > Sr(II) > Ca(II) at 25 °C, respectively. The factors influenced the alginate affinity for chelating the metal ions were explained in some correlation terms between the alginate capacity and some physicochemical properties of chelated metal ions and its respective formed complexes. Speculated geometrical configurations for chelation were suggested and discussed.

Design of all-solid-state chloride and nitrate ion-selective electrodes using anion insertion materials of electrodeposited poly(allylamine)-MnO2 composite

All-solid-state ion-selective electrodes as potentiometric ion sensors for the determination of chloride (Cl−) or nitrate (NO3−) ions were designed by inserting an electrodeposited composite layer consisting of manganese dioxide and poly(allylamine), a polymeric cation, as the inner solid-contact layer between the electrode substrate and poly(vinyl chloride) (PVC)-based ion-sensitive membrane containing the corresponding ionophores for Cl− or NO3− ions. The double-layered ion-selective electrodes exhibited selective and quick (≤10 s) potential response for the anions; moreover, the Nernstian slopes of the calibration curves of the electrodes were adequate, and the electrodes presented a wide detection range (10−5–10−1 mol dm−3). As the poly(allylamine)-manganese dioxide composites presented anion-insertion redox activity, the insertion of composite layers was highly effective in stabilizing the membrane potential of PVC because it lowered the impedance at the electrode interface, resulting in quicker responses to the anion activity in analytes than those of the corresponding electrodes without composite layers.

Synthesis and Applications of Polymeric Reagent p-Substituted Triphenylamine

Chemical modification of chloromethylstyrene - styrene copolymer throughout reaction of p-substituted carboxylic acid group of bis-(4,4`-dibromo)-4``-triphenylamine carboxylic acid with the chloromethyl group attached to a phenyl group was carried out on soluble copolymer and polymeric cross-linked copolymer. Chemical oxidation of the neutral p-substituted triphenylamine with antimony pentachloride in dichloromethane solvent gives the corresponding cation - radical salt with the counter ion antimony hexachloride (SbCl6-). The isolated deep blue color cation radical salt is soluble or in insoluble (resin) form in the copolymer was used as a thermal cationic initiator for the polymerization of epoxy and vinyl monomers at room temperature. The cation radical resin showed good activity and stability compared to the soluble polymeric cation radical, both can initiate the cationic polymerization of cyclohexene oxide and N-vinylcarbazole in dichloromethane at room temperature.

Behaviors of Desorption Agents During Removal of Cs From Clay Minerals and Actual Soil

The behaviors of various desorption agents were investigated during the desorption of cesium (Cs) from samples of clay minerals and actual soil. Results showed that polymeric cation exchange agents (polyethyleneimine (PEI)) efficiently desorbed Cs from expandable montmorillonite, whereas acidic desorption solutions containing HCl or PEI removed considerable Cs from hydrobiotite. However, most desorption agents could desorb only 54% of Cs from illite because of Cs’s specific adsorption to selective adsorption sites. Cs desorption from an actual soil sample containing Cs-selective clay mineral illite ( PEI > NH4+, and the highest Cs desorption amount achieved using HCl was 83%. Unlike other desorption agents with only cation exchange capabilities, HCl can attack minerals and induce dissolution of metallic elements. HCl’s ability to both alter minerals and induce H+/Cs+ ion exchange is expected to promote Cs desorption from actual soil samples.

Polycationic Polymer Layer for Air-Stable and Dendrite-Free Li Metal Anodes in Carbonate Electrolytes.

The short cycle life and safety concerns caused by uncontrollable dendrite growth have severely hindered the commercialization of lithium metal batteries. Here, a polycationic and hydrophobic polymer protective layer fabricated by a scalable tape-casting method is developed to enable air-stable, dendrite-free, and highly efficient Li metal anodes. The polymeric cations of poly(diallyl dimethyl ammonium) (PDDA) provide an electrostatic shielding effect that unifies Li+ flux at the surface of the Li anode and promotes a homogeneous Li plating, while the bis(trifluoromethanesulfonyl)imide (TFSI) anions bring hydrophobic characteristics and improve moisture stability. The accumulated TFSI anions by the polycationic film also facilitate the formation of a stable solid electrolyte interphase (SEI). Steady Li plating/stripping in the carbonate electrolyte can be achieved under a high areal capacity of 10 mAh cm-2 for 700 h with Li utilization efficiency up to 51.6%. LiNi0.8 Mn0.1 Co0.1 O2 and LiFePO4 cells using the modified anode exhibit much improved electrochemical performance compared with the bare Li counterpart. Moreover, ultrasonic imaging shows no gas generation in the modified Li/LiFePO4 pouch cell. Mechanism investigation demonstrates the stable SEI and homogeneous Li deposition derived by the polycationic layer.

Polyethylenimine-mediated controlled synthesis of Prussian blue-gold nanohybrids for biomedical applications.

We report on polyethylenimine (PEI)-mediated synthesis of Prussian blue nanoparticles (PBNPs) and gold nanoparticles (AuNPs); the formation of PBNP-AuNP nanohybrids with a remarkable change in Prussian blue character as a function of gold cation concentration was also considered. It was shown that PEI-protected polycrystalline PBNPs can be synthesized in an acidic medium from the precursor potassium ferricyanide [K3Fe(CN)6] at 60 °C. Since PEI also enables the controlled formation of gold nanoparticles (AuNPs) in the presence of formaldehyde under ambient conditions, nanohybrids of PBNPs and AuNPs were prepared. The formation of AuNPs was recorded over a wide range of PEI concentrations, which allowed control over polymeric cation capping of the AuNPs. PEI concentration-dependent enhancement/quenching of fluorescence/resonance Rayleigh scattering was useful for non-enzymatic detection of serum glucose levels. The resonance Rayleigh scattering intensity of PBNPs was several-fold higher than that of AuNPs and acted as a potent quencher of fluorescence. At an optimal concentration of PEI, AuNPs allowed an increase in the fluorescence signal as function of glucose concentration; the quenching ability of PB was demonstrated to be a function of the glucose concentration. This method is efficient for fast glucose sensing and offers a wider linear dynamic range, 0-10 mM, which is useful for non-enzymatic detection of serum glucose levels.

Selective Recovery of Ammonia Nitrogen from Wastewaters with Transition Metal-Loaded Polymeric Cation Exchange Adsorbents.

Extracting valuable products from wastewaters with nitrogen-selective adsorbents can offset energy-intensive ammonia production, rebalance the nitrogen cycle, and incentivize environmental remediation. Separating nitrogen (N) as ammonium from other wastewater cations (e.g., K+ , Ca2+ ) presents a major challenge to N removal from wastewater and N recovery as high-purity products. High selectivity and capacity were achieved through ligand exchange of ammonia with ammine-complexing transition metals loaded onto polymeric cation exchange resins. Compared to commercial resins, metal-ligand exchange adsorbents exhibited higher ammonia removal capacity (8 mequiv g-1 ) and selectivity (N/K+ equilibrium selectivity of 10.1) in binary equimolar solutions. Considering optimal ammonia concentrations (200-300 mequiv L-1 ) and pH (9-10) for metal-ligand exchange, hydrolyzed urine was identified as a promising candidate for selective TAN recovery. However, divalent cation exchange increased transition metal elution and reduced ammonia adsorption. Ultimately, metal-ligand exchange adsorbents can advance nitrogen-selective separations from wastewaters.

Preparation and application of CPC/Keggin-Al30 modified montmorillonite composite for Cr (VI) removal

To enhance the adsorption performance of natural calcium-based montmorillonite (Ca-MMT), the polymeric hydroxyaluminum cation - Keggin-Al30 ([Al30O8(OH)56(H2O)24]18+) and cetylpyridinium chloride (CPC) were used to modify Ca-MMT for preparation of CPC-Al30 pillared montmorillonite composite (CPC-Al30PMT). The CPC-Al30PMT was characterized via analysis of its chemical and physical structure, morphology, surface properties, and zeta potential. The results showed that the Al30 polymer cation and CPC successfully intercalated into the interlayer of Ca-MMT, which increased the d001 value from 1.47 nm to 1.93 nm, and increased the pore volume correspondingly. The zeta potential was reversed from negative to positive after modification, presenting a possibility to adsorb anionic contaminants from water. The investigation of hexavalent chromium (Cr (VI)) adsorption on CPC-Al30PMT showed that the removal of Cr (VI) was positively correlated with the dosage of adsorbent, and negatively correlated with the initial concentration of Cr (VI), the ionic strength and the initial pH of the solution. CPC-Al30PMT showed good Cr (VI) removal performance, with the maximum adsorption (qe) of 42.44 mg/g. The adsorption process conformed to Freundlich model and pseudo-second-order kinetic model. Thermodynamics studies showed that adsorption was a spontaneous exothermic process. Electrostatic interaction, ion exchange and reduction were the main mechanisms of the removal.

Automated accelerated solvent extraction coupled with ultra-high-performance liquid chromatography for the analysis of piperazine in egg samples

This study involved the development of an ultra-high-performance liquid chromatography-fluorescence method for rapid detection of piperazine residues in eggs. Accelerated solvent extraction, a rapid and efficient sample extraction technique, was used to extract piperazine from egg samples (whole egg, albumin and yolk). Ground eggs were subjected to accelerated solvent extraction using n-hexane in the first step and acetonitrile-formic acid (98:2, v/v) in the second step and were then purified by a solid phase extraction cartridge using polymeric strong cation sorbents. The collected eluate was placed on a nitrogen blower and dried. After reconstitution with acetonitrile, piperazine was derivatized with dansyl chloride and catalytic triethylamine. A portion of the precipitate was removed using a 0.22 μm needle filter (organic-phase) and injected into the separation system for analysis. The analyte was separated using an Acquity HSS T3 [100 × internal diameter (i.d.) 2.1 mm, 1.8 µm] ultra high performance liquid chromatography column that was coupled with a fluorescence detector. Under the optimum conditions, the linear ranges were 3.5–400.0 μg/kg for the whole egg and yolk and 4.2–400.0 μg/kg for the albumin, the extraction recoveries were ≥ 77.07%, and the precision values were ≤ 6.63%. The limit of detection and limit of quantification values were 1.05–1.32 and 3.50–4.20 μg/kg, respectively. The method was successfully applied for the analysis of piperazine in egg (whole egg, albumin and yolk) samples.

Synthesis and crystal structure of a 6-chloro-nicotinate salt of a one-dimensional cationic nickel(II) coordination polymer with 4,4'-bi-pyridine.

A 6-chloro-nicotinate (6-Clnic) salt of a one-dimensional cationic nickel(II) coordination polymer with 4,4'-bi-pyridine (4,4'-bpy), namely, catena-poly[[[tetra-aqua-nickel(II)]-μ-4,4'-bi-pyridine-κ2 N:N'] bis-(6-chloro-nicotinate) tetra-hydrate], {[Ni(C10H8N2)(H2O)4](C6H3ClNO2)2·4H2O} n or {[Ni(4,4'-bpy)(H2O)4](6-Clnic)2·4H2O} n , (1), was prepared by the reaction of nickel(II) sulfate hepta-hydrate, 6-chloro-nicotinic acid and 4,4'-bi-pyridine in a mixture of water and ethanol. The mol-ecular structure of 1 comprises a one-dimensional polymeric {[Ni(4,4'-bpy)(H2O)4]2+} n cation, two 6-chloro-nicotinate anions and four water mol-ecules of crystallization per repeating polymeric unit. The nickel(II) ion in the polymeric cation is octa-hedrally coordinated by four water mol-ecule O atoms and by two 4,4'-bi-pyridine N atoms in the trans position. The 4,4'-bi-pyridine ligands act as bridges and, thus, connect the symmetry-related nickel(II) ions into an infinite one-dimensional polymeric chain extending along the b-axis direction. In the extended structure of 1, the polymeric chains of {[Ni(4,4'-bpy)(H2O)4]2+} n , the 6-chloro-nicotinate anions and the water mol-ecules of crystallization are assembled into an infinite three-dimensional hydrogen-bonded network via strong O-H⋯O and O-H⋯N hydrogen bonds, leading to the formation of the representative hydrogen-bonded ring motifs: tetra-meric R 2 4(8) and R 4 4(10) loops, a dimeric R 2 2(8) loop and a penta-meric R 4 5(16) loop.