Metal Ions Zn Research Articles

Combined experimental, DFT theoretical calculations and biological activity of sulfaclozine azo dye with 1-hydroxy-2-naphthoic acid and its complexes with some metal ions

Sulfaclozine-1-hydroxy-2-naphthoic acid azo dye (Scna) and its metal complexes with Ni(ii) Cu(ii), Zn(ii) and Pd(ii) metal ions have been prepared and characterized using different techniques.

Coordination chemistry of some new Mn(II), Cd(II) and Zn(II) macrocyclic Schiff base complexes containing a homopiperazine head unit. Spectral, X-ray crystal structural, theoretical studies and anticancer activity

Here we report a number of novel macrocyclic Schiff base complexes with a homopiperazine skeleton. These symmetrical pentaaza macrocyclic Schiff base complexes were prepared via a template approach, based on the condensation reaction of an amine containing homopiperazine moiety and 2,6-diacetylpyridine or 2,6-pyridine dicarboxaldehyde in 1:1 mol ratio in the presence of Cd(II), Mn(II) and Zn(II) metal ions. These Schiff base complexes were characterized by elemental analyses, FT-IR, mass spectrometry and, in the cases of diamagnetic Zn(II) and Cd(II) complexes, 1H and 13C NMR spectroscopy. As well, the structures of [Mn(L1)(CH3OH)(ClO4)]ClO4 and [Cd(L2)(H2O)2](ClO4)2 have been determined by X-ray structural analyses, where the L1 and L2 are the products of the reaction of the new amine with 2,6–Pyridinedicarboxaldehyde or 2,6–diacetalpyridine, respectively. The coordination environment of the metal atoms in both of these complexes is best described as a distorted pentagonal bipyramid. The cytotoxic activities of these new complexes were also examined. The potency of complexes to induce cell death was screened on A2780, U37 MG, and H1299 cell lines, compared to doxorubicin which was used as a control. The results reveal that in some cases, the cytotoxic activity of complexes was stronger than that of doxorubicin as standard. Also, the bonding situation in the complexes, were analyzed by NBO and energy-decomposition analysis (EDA) and EDA-NOCV analysis.

Comparative optical studies of naphthalene based Schiff base complexes for colour tunable application

Abstract Two Schiff base ligands were synthesized by the chemical reaction of 2,3-diaminonaphthalene with salicylaldehyde (HL1) and 2,3-diaminonaphthalene with 2-hydroxy-1-naphthaldehyde (HL2). The ligand HL2 have an additional phenyl group in the structure compared to HL1. This additional phenyl group in the molecular structure is expected to modify the optical and photometric properties of the ligand. The complexation of Zn metal ions with ligands occur via N-azomethine followed by the deprotonation of OH group. The complexes HC1 and HC2 were characterized by FTIR, HNMR, UV-VIS and PL techniques. The optical properties like absorption and fluorescence were studied to get the idea about the transitions among molecular orbitals as well as quantum yield. The complex having an additional phenyl group shows a blue shift in emission wavelength with an improvement in quantum yield. HOMO-LUMO energy gap along with some molecular parameters were estimated in order to know the chemical reactivity as well as to understand charge transfer process in the ligands and complexes.

Synthesis, characterization and catalytic application of ZnPO molecular sieve in wastewater system

In the present work, phosphatizing and organic double wastewater were reused to synthesize ZnPO molecular sieves with a hydrothermal method. Enhanced application of the samples was carried out through cyclohexane oxidation and Michael addition alkylation reaction. The removal efficiency of Zn, P in phosphatizing wastewater was over 90%. The characterizations like the crystallite phases, surface morphology and porous features were also confirmed. The catalytic efficiencies of ZnPO prepared in double wastewater system had a good catalytic performance in cyclohexane oxidation and Michael addition reactions, which were much higher than that of the catalyst prepared via simulated system. The surface features of catalysts had a close relationship with such results. These outstanding characters were attributed to more active centers formation, which were brought through interaction of Zn, P, and other metal ions in phosphatizing wastewater, as well as the huge surface area caused by the organic materials in organic wastewater.

Adsorption studies of zinc(II) on magnetite, baobab (Adansonia digitata) and magnetite\u2013baobab composite

The negative effect of high concentration of heavy metals in the environment on living species prompted this research. A study of adsorption of zinc on synthesized magnetite (MG), baobab fruit shell (BB) and magnetite–baobab composite (MB) was carried out. The adsorption of Zn(II) ions was examined using batch equilibrium technique. The effects of initial metal ions concentrations (15–150 mg/L for zinc), adsorbent dose (0.05–0.3 g), contact time (5–150 min), pH (2–8) and temperature (303–343 K) on the sorption capacity of these adsorbents were investigated. The Zn(II) ions at a solution concentration of 150 mg/g gave maximum adsorption capacity of 38.25, 33.95 and 29.20 mg/g for MB, MG and BB, respectively. The adsorption of Zn(II) metal ions was modelled using Langmuir, Freundlich and Temkin isotherms. The highest correlation coefficient (R2) value was obtained from Freundlich model for Zn(II) adsorption on MG and MB as 0.986 and 0.973, respectively, while that of Zn(II) on BB was obtained from Langmuir model as 0.993. The kinetic and thermodynamic studies revealed that the adsorption processes followed pseudo-second-order kinetics and were endothermic in nature. Desorption experiments were conducted on the spent adsorbent using 0.1, 0.2, 0.5, 1.0 and 2.0 M HCl to determine the reusability potentials of the adsorbents. There was an decrease in the amount of Zn(II) ions adsorbed after each stage of desorption process varied between the different acid concentrations. The 0.1 M HCl gave the highest degree of adsorption for Zn(II) on BB, while 0.2 M HCl was the best for MG and MB.

Chelate based phytoremediation study for attenuation of chromium toxicity stress using lemongrass: Cymbopogon flexuosus (nees ex steud.) W. Watson

Chelate employed wrenching out of Chromium from contaminated soils is a comparably new technology. The pot culture experiments were carried out to study the toxicological, physiological and biochemical changes in Lemongrass using different chelators such as Ethylenediaminetetraaceticacid (EDTA), Diethylenetriaminepentaacetic acid (DTPA), Citric acid (CA) and Salicylic acid (SA) and metal ions (Fe, Mg and Zn) in Cr+6 contaminated soil. The application of heavy metal Cr induced number of adverse consequences like reduction in root/shoot length, biomass and chlorophyl content in Lemongrass plants grown in soil with Cr+6 (50mgkg−1). On the contrary, the growth of Lemongrass was stimulated by the addition of chelators such as EDTA, DTPA, Citric acid, salicylic acid including metal ions (Fe, Mg and Zn). The increase in proline content was associated with the synthesis of antioxidant enzymes by the applications of chelators and metal ions. The treated plants with reduced Transportation index (Ti) values indicated more root Chromium accumulation as compared to shoot. The Bio-Concentration Factor (BCF) and Total Accumulation Rate (TAR) of Chromium were elevated with the supplementation of chelators and metal ions, thus, illustrating more metal bioavailability in plants.

Luminescent Sensing, Selective Extraction and Recovery of Cu2+ from Aqueous Environment by a Novel Turn-on Chemosensor.

A novel luminescent hydrazone ligand was synthesized via 1:1 condensation reaction of 9-anthracene aldehyde and 2-hydrazinobenzoic acid followed by its characterization with the help of absorption, emission, FTIR, NMR and mass studies. It was investigated as a reversible, ratiometric and turn-on luminescent chemosensor for Cu2+ in aqueous environment. The receptor shows a prominent color change in presence of Cu2+ from yellow to reddish brown in DMSO-H2O (2:1) medium. Upon addition of Cu2+, a remarkable increment in emission intensity (Φ = 0.091, 11 fold) was observed probably due to intra-ligand charge transfer transition (ILCT). Interestingly, this sensor is capable to extract Cu2+ selectively from aqueous mixture of metal ions using dichloromethane solvent with the increased extraction efficiency from 85% (L:Cu2+, 1:1) to 95% (L:Cu2+, 2:1) in the pH range of 6.5-10.0. The extraction behavior of Cu2+ was monitored with the help of UV-Vis spectroscopy and a readily-usable smartphone to capture the RGB data which may be helpful as a field based analysis tool. In presence of Cu2+ (1.0 × 10-5M), no significant interference was observed after addition of 5-fold excess of other metal ions (Zn2+, Cd2+, Co2+, Fe2+, Fe3+, Ni2+, Hg2+, Sn2+, Al3+, Cr3+, Mn2+) in DMSO-H2O (2:1) medium. Moreover, the ligand was regenerated (> 98%) by adjusting the pH upto 4cycles and showed a good recyclability and reusability which might be helpful to extract Cu2+ efficiently from aqueous medium.

Complexation behavior of 6,6″-dimethyl-2,2′:6′,2″-terpyridine ligand with Co(II), Au(III), Ag(I), Zn(II) and Cd(II) ions: Synthesis, spectroscopic characterization and unusual structural motifs

Despite the fact that the ‘tpy’ binding motif has been extensively documented, observation of the unusual coordination motifs makes the preprogrammed assembly of functional materials an up-to-date challenge. Drawing inspiration from our previous experience with 6,6″-dimethyl-2,2′:6′,2″-terpyridine ligand (L), we have thus focused on its complexation behavior with Co(II), Au(III), Ag(I), Zn(II) and Cd(II) metal ions, stemming from their applicative relevance. As a result, ten new coordination compounds were synthesized of the following molecular formulae: [CoL(NO3)2] (1), [CoL2]2(ClO4)4·5H2O (2), [CoL(MeOH)(CF3SO3)2] (3), [Co(Lox)(CH3SOCH3)(CF3SO3)]CF3SO3 (3a), [(LH2)2+·2AuCl4−·H2O] (4), [(Au(LH)Cl3)+·AuCl4−] (5), [AgL(O-NO2)]3[(AgL(O2-NO)] (6), [AgL(NCCH3)]BF4·CH3CN] (7), [ZnL(CF3SO3)2] (8), [CdL(NO3)2·CdLBr2] (9), as unambiguously confirmed by single-crystal X-ray diffraction studies. To our surprise, most of the presented structures are to the certain level unique; either considering incomplete tridentate coordination of the tpy ligand L (4, 5), its oxidative transformation (3a) or the formation of mixed solid state solutions (9). Each compound was fully characterized by a series of analytical techniques, including elementary analysis, FT-IR, ESI-MS and 1H NMR, the latter two of which allowed us to gain insight into their solution behavior.

Synthesis, characterization, DFT and antimicrobial studies of transition metal ion complexes of a new schiff base ligand, 5-methylpyrazole-3yl-N-(2́-hydroxyphenylamine)methyleneimine, (MPzOAP)

A new pyrazole based ‘NNO’ tridentate ligand, 5-methylpyrazole-3yl-N-(2́-hydroxyphenylamine)methyleneimine, (MPzOAP) was synthesized and characterized by elemental analyses, mass, IR, 1H NMR spectral parameters. The versatile coordination mode of the ligand was established by the synthesis of Co(III), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) metal ion complexes. These complexes were characterized by elemental analyses, conductance and magnetic susceptibility measurements, UV–Vis, IR, 1H NMR spectroscopy, PXRD and thermal analysis. The structures of the ligand and complexes were also investigated using the DFT method. The ligand structure contains the coordination function of the tertiary nitrogen atom of pyrazole ring, the azomethine nitrogen and the phenolic oxygen atom, suitably spaced for chelation with a metal ion and acting as a ‘NNO’ tridentate donor ligand. In vitro antimicrobial activity of the reported ligand and the metal ion complexes were screened and the mode of action was also studied by scanning electron microscopy (SEM) against some pathogenic bacteria.

Adaptive Neuro-fuzzy Inference System Prediction of Zn Metal Ions Adsorption by γ-Fe2o3/Polyrhodanine Nanocomposite in a Fixed Bed Column

This study investigates the potential of an intelligence model namely, Adaptive Neuro-Fuzzy Inference System (ANFIS) in prediction of the Zn metal ions adsorption in comparision with two well known empirical models included Thomas and Yoon methods. For this purpose, an organic-inorganic core/shell structure, γ-Fe2O3/polyrhodanine nanocomposite with γ-Fe2O3 nanoparticle as core with average diameter of 15 nm and polyrhodanine as shell with thickness of 3 nm, was synthesized via chemical oxidation polymerization. The properties of adsorbent were characterized with transmission electron microscope (TEM) and Fourier transform infrared (FT-IR) spectroscopy. Sixty seven experimental data sets including the treatment time (t), the initial concentration of Zn (Co), column height (h) and flow rate (Q) were used as input data to predict the ratios of effluent-to-influent concentrations of Zn (Ct/C0). The results showed that ANFIS model with the R coefficient of 0.99 can predict Ct/C0 more accurately than empirical models. Also it was found that the result of the Thomas and Yoon methods with R coefficient of 0.828 and 0.829, respectively were so close to each other. Finally, performance of our ANFIS model was compare to Thomas and Yoon methods in two different conditions, i.e. variable initial influent concentration and variable column height. High performance of ANFIS model was proved by the comparitive results.

Synthesis and characterization of chromone-based ligand and its fluorescence property towards Zn2+

Zinc (Zn) is a type of element that are commonly found in the Earth’s environment and may be originated either naturally from the environment or produced by human activities. Zn has been identified as a hazardous metal which can give harmful effects to human health and Earth’s environment. Therefore, it is very important to develop a simplest method which does not require laborious work in order to detect Zn metal ions. Ligand of AFCMSH was synthesized by the mean of reflux reaction between 2-amino-3-formylchromone (AFC) and 4methylbenzenesulfonylhydrazide (MSH). The molecular structure of the ligand in the ground state was optimized using density functional theory (DFT/B3LYP) method with 6-311G(d,p) basis set. Characterization of ligand was conducted using spectroscopic techniques such as Fourier Transform Infra-Red spectroscopy (FT-IR), Gas Chromatography Mass Spectrometry (GC-MS), Nuclear Magnetic Resonance spectroscopy (NMR) and Ultraviolet-visible spectroscopy (UV-VIS). Meanwhile the fluorescence property of ligand in the presence of metal cations was recorded using Fluorescence Spectrophotometer. Ligand shows almost no fluorescence property in the presence of various metal ions except for Zn2+ ion when observed under UV light. Interestingly, ligand exhibits a remarkable fluorescence response by giving yellow-green fluorescence with strong fluorescence intensity in the emission spectrum at 501nm at excitation of 375 nm upon addition of one equivalent of Zn2+.

Treatment and water reuse of lead-zinc sulphide ore mill wastewaters by high rate dissolved air flotation

Simulated wastewaters (concentrate and tailings thickener overflows), from a future lead-zinc flotation separation plant, were treated for the removal of target metal ions (Zn2+, Pb2+ and Cu2+) and suspended solids (0.1–0.5 g L−1). The ions were adsorbed onto ferric hydroxide precipitates, and then removed by dissolved air flotation (DAF). Best results obtained at bench scale were validated at pilot scale, employing i. 15–20 mg L−1 Fe3+ (chloride salt); ii. Flocculation in two units (rapid mixing - G > 120 s−1, and slow mixing - G = 20–80 s−1), with 0.2–0.5 mg L−1 of flocculant (a cationic polyacrylamide); iii. DAF at a saturation pressure of 6 bar and a 20% water recycling rate. The removal of ions between pH 6.5 and 7.5 was very high, reaching separation efficiencies up to 95% for Pb2+ and Cu2+ ions (potential activators of ZnS); the adsorption mechanisms of the uptake of the ions were discussed. The suspended solids (fine particles, <44 µm) were separated by DAF (89–96%) to concentrations <0.5 g L−1. For higher solid contents, the formed flocs became larger, difficult-to-float and operating conditions required less flocculant and a higher recycling ratio. These high separation efficiencies allowed reuse of water in the lead/zinc sulphide ore rougher flotation stage, avoiding the activation of ZnS flotation. The pilot DAF unit (1.8–2.4 m3 h−1 flow rate) followed an innovative design by enhancing the height/area rate (6.9 m−1), compared to conventional cells; it included specially designed and oriented lamellae and a perforated plate to control internal turbulence. These modifications allowed the enhancement of the hydraulic loading capacity up to 15 m3 m−2 h−1 (or 15 m h−1), more than double the known value for conventional DAF cells (about 7 m h−1). Estimations of general costs for a 300 m3 h−1 treatment plant were calculated and the operating costs reached US$ 0.56 m−3 of treated water. It is believed that this DAF process has a high potential for removing deleterious ions from water at a high removal rate, recycling process water feeding ore flotation plants and minimizing effluent discharge (sometimes polluted).

Series of Mn(II)/Mg(II)/Zn(II) Coordination Polymers with Azo/Alkene Functionalized Ligands

A series of six novel coordination polymers based on Mn(II)/Mg(II)/Zn(II) metal ions with azo/alkene functionalized carboxylic acid have been synthesized and well-characterized using several state-of-art techniques. Compound 1, {[Mn2(ABDCA)2(DPE)(DMF)2]·2DMF}n, (where ABDCA = Azobenzene-4,4′-dicarboxylic acid, DPE = 1,2-Di(4-pyridyl)ethylene, and DMF = N,N′-Dimethylformamide) is a three-dimensional structure with threefold interpenetration. Compound 2, {[Mn3(ABDCA)3(DMF)4]·2DMF}n contains Mn3O16 cluster unit which is connected with ABDCA ligands to form a two-dimensional layered structure. Compound 3, {[Mg3(ABDCA)3(DMF)4]·4DMF}n contains Mg3O16 clusters, associated with ABDCA ligands, forming the 3D structure. Coordination polymers 4 and 5 ({[Zn(ABDCA)(2,2′-BPy)]·H2O}n, (4), {[Zn(SDCA)(2,2′-BPy]}n, (5)), respectively, (where SDCA = stilbene-4,4′-dicarboxylic acid and 2,2′-BPy = 2,2′-Bipyridine) are identical structures with a difference in carboxylate ligand. In both cases, the one-dimensional chains are ...

Preparation, spectroscopic characterization, thermal stability and XRD of some new metalchelates with aceclofenac in presence of 1,10-phenanthroline

In this study, mixed ligand complexes derived from aceclofenac (Acecl) as primary ligand and 1,10-phenanthroline (Phen) as secondary ligand have been prepared and characterized by conventional techniques including elemental analyses, infrared, electronic spectra, 1H NMR and XRD. The infrared spectral data showed that the chelation behavior of the ligands towards Ni(II), Cu(II), Zn(II), Zr(IV) and La(III) transition metal ions is through oxygen of ketone, carboxylic group of aceclofenac and nitrogen atom of 1,10-phenanthroline. Thermal analyses showed that the chelates lose water molecules of hydration initially and subsequently expel anionic part and organic ligands in continuous steps leaving metal or metal oxide as a final product. XRD analysis of the compounds showed that, Acecl, Phen and their metal complexes display crystalline peaks.

Metal Coordination to Unsymmetric 1,n′‐Disubstituted Ferrocene Histidine Peptides

In this study, the coordination chemistry of unsymmetrical 1,n′‐substituted ferrocene (Fc) peptide conjugates is explored, where the peptide substituents are two different histidine‐containing peptides. The resulting Fc‐conjugates serve as ligands for the formation of metal complexes, with the intention to generate complexes that possess a labile coordination site. The following Fc[CO‐His(Trt)‐OMe][COOMe] (1), Fc[CO‐His(Trt)‐Gly‐OMe][CO‐Gly‐OMe] (2), Fc[CO‐His(Trt)‐His(Trt)‐OMe][CO‐His(Trt)‐OMe] (3), and Fc[CO‐His(Trt)‐Gly‐His(Trt)‐OMe][CO‐Gly‐His(Trt)‐OMe] (4) were synthesized and characterized. Each compound forms discrete complexes with metal divalent metal ions Zn2+, Co2+ and Cd2+, where a single metal ion is complexed by the metallo‐ligand, as was confirmed spectroscopically. The redox properties of the Fc group are influenced by metal coordination to the peptide substituents and anodic shifts occur upon the addition of metal ions. These follow the order Zn2+ &gt; Cd2+ &gt; Co2+. NMR experiments indicated imidazole rings are the site of metal coordination. Fc‐peptide conjugates display a switchable axial chirality that is dependent on metal complexation.

Discrete Triptycene-Based Hexakis(metalsalphens): Extrinsic Soluble Porous Molecules of Isostructural Constitution.

In 2013 the concept of OMIMs (organic molecules of intrinsic microporosity) was introduced by McKeown et al. These OMIMs are constructed on the basis of rigid molecular cores such as triptycene, spirobifluorenes, and others. Like shape-persistent organic cages, these are soluble discrete molecules and therefore an interesting alternative to 3D, insoluble porous materials, such as metal-organic frameworks, covalent-organic frameworks, or zeolites. OMIMs are chemically and thermally robust because the formation of strong covalent bonds has been used for their synthesis. To date, a few OMIMs have been reported, though most of them did not contain any functional unit to enhance gas sorption properties. This work introduces an isostructural series of metal-salphene based OMIMs with different metal ions (Zn2+ , Ni2+ , Cu2+ , Pd2+ , and Pt2+ ) integrated into the backbone. The influence of the metal centers on interaction with gas molecules has been investigated by gas sorption experiments.

Accelerated crystallization of magnetic 4A-zeolite synthesized from red mud for application in removal of mixed heavy metal ions

To cope with the increasing environmental issues of red mud, an integrated technological route for its comprehensive utilization was developed through the extraction of valuable components and the synthesis of magnetic 4A-zeolite. To accelerate the crystallization process of the synthesized 4A-zeolite, sodium chloride (NaCl) was innovatively employed under hydrothermal treatment. The effects of various parameters, including mass ratio of red mud/NaOH, alkali fusion temperature, alkali fusion time and molar ratio of NaCl/Al2O3, were systematically investigated. The results showed that approximately 81.0% Al, 76.1% Si and 95.8% Fe were utilized from red mud using alkali fusion and acid leaching methods. The optimal conditions of the alkali fusion process were determined as: mass ratio of red mud/NaOH = 1/2, alkali fusion temperature of 800 °C, and time of 90 min. Furthermore, when the molar ratio of NaCl/Al2O3 was kept at 1.5, the crystallization time reduced from 240 min to 150 min, and particle size distributions narrowed from 20–100 μm to 1–10 μm. The practical applications in removal of mixed heavy metal ions (Zn2+, Cu2+, Cd2+, Ni2+, and Pb2+) from wastewater indicated that the as-synthesized magnetic 4A-zeolite is a promising candidate for heavy metals adsorption.

Sustainable nitrogen-rich hierarchical porous carbon nest for supercapacitor application

Chitosan has high synthetic flexibility, making it a promising nitrogenous bioresource for industrial applications. Nitrogen-rich hierarchically porous carbon (NHPC) was successfully synthesized by hydrothermal carbonization and self-activation of a chitosan-transition metal ion (Zn2+) complex. The N2 adsorption-desorption isotherm revealed that the as-made NHPC had large specific surface area (1067 m2 g−1) and a unique hierarchical pore structure (0.6–6.4 nm). Scanning electron microscopy (SEM) indicated a 3D finely interconnected nest architecture for NHPC. X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the nitrogen atoms in the chitosan were protected by coordination with zinc ions, and most of them were still retained in the carbon matrix (6.36 at%) after high temperature activation. Electrochemical measurements exhibited that NHPC delivers a high specific capacitance (228.7 Fg−1 at 1 A g−1), impressive rate capability (the specific capacitance at 20 A g−1 was 174 Fg−1, maintaining 74.6% of the initial capacitance at 0.5 A g-1), and outstanding long-term cycling stability (98.3% retention after 5000 cycles), together with excellent energy density of 25.7 Wh kg-1 at the power density of 500 W kg-1. This study offers a novel strategy for synthesizing NHPC as one of the desirable electrode material candidates for energy storage.

Efficient removal of Co(II), Ni(II), and Zn(II) metal ions from binary and ternary solutions using a pH responsive bifunctional graft copolymer

A novel, pH responsive graft copolymer hydroxyethyl cellulose-graft-poly(N-vinyl imidazole-co-acrylic acid) containing both acidic and basic functionalities was prepared in water medium by using potassium peroxydisulfate as an initiator. Several techniques like FTIR, XRD, NMR, SEM and TGA/DTGA studies were used to characterize the synthesized copolymer. The polymer was used for the adsorption of toxic heavy metal ions namely Co(II), Ni(II) and Zn(II) from the ternary mixture of three metal ion’s solution in aqueous medium. The graft copolymer showed an excellent pH dependence for the adsorption of aforementioned three metal ions. Ni(II) and Co(II) showed maximum adsorption efficiency at pH 5.5, whereas for Zn(II), it was at 6.5. Metal complexation studies by the synthesized graft copolymer were carried out experimentally by using conductometric titration and theoretically by Density Functional Theory (DFT) using Gaussian 09 software. Metal complexation studies showed that at low pH (≤ 5.5), it is the carboxylic acid group, and at pH > 5.5, it is only the carboxylic acid and imidazole functionalities that both are responsible for the adsorption. Adsorption dynamics, isotherms, kinetics and thermodynamics were studied for all the three metal ions’ adsorption onto the polymer surface. The adsorption follows Langmuir isotherm model and pseudo-second-order kinetics for all the metal ions. Maximum adsorption capacity was found to be 165, 122 and 68 mg/g for Ni(II), Co(II) and Zn(II) metal ion, respectively. Thermodynamic study showed that the adsorption process was endothermic and spontaneous in nature. The preferential metal adsorption by the graft copolymer was followed in the order Ni(II) > Co(II) > Zn(II).

An Azoaromatic Ligand as Four Electron Four Proton Reservoir: Catalytic Dehydrogenation of Alcohols by Its Zinc(II) Complex.

Electroprotic storage materials, though invaluable in energy-related research, are scanty among non-natural compounds. Herein, we report a zinc(II) complex of the ligand 2,6-bis(phenylazo)pyridine (L), which acts as a multiple electron and proton reservoir during catalytic dehydrogenation of alcohols to aldehydes/ketones. The redox-inactive metal ion Zn(II) serves as an oxophilic Lewis acid, while the ligand behaves as efficient storage of electron and proton. Synthesis, X-ray structure, and spectral characterizations of the catalyst, ZnLCl2 (1a) along with the two hydrogenated complexes of 1a, ZnH2LCl2 (1b), and ZnH4LCl2 (1c) are reported. It has been argued that the reversible azo-hydrazo redox couple of 1a controls aerobic dehydrogenation of alcohols. Hydrogenated complexes are hyper-reactive and quantitatively reduce O2 and para-benzoquinone to H2O2 and para-hydroquinone, respectively. Plausible mechanistic pathways for alcohol oxidation are discussed based on controlled experiments, isotope labeling, and spectral analysis of intermediates.