Recyclable iron(ii) caffeine-derived ionic salt catalyst in the Diels–Alder reaction of cyclopentadiene and α,β-unsaturated N-acyl-oxazolidinones in dimethyl carbonate

Iron(ii) triflate was used in combination with caffeine-derived salts as recyclable catalysts for the Diels–Alder reaction run in dimethyl carbonate (DMC) as a green solvent. The catalyst was prepared as an ionic salt from a xanthinium salt and Fe(OTf)₂. Various substrates including α,β-unsaturated carbonyl and N-acyloxazolidinone derivatives were reacted with cyclopentadiene using this recyclable catalyst. The use of a low catalyst loading (1 mol%) afforded high yields (up to 99%) of the corresponding cycloadducts. The recycling and the efficiency of the catalyst were demonstrated for several runs.

Iron(ii) triflate was used in combination with caffeine-derived salts as recyclable catalysts for the Diels–Alder reaction run in dimethyl carbonate (DMC) as a green solvent.     

Synthesis,characterization and cytotoxicity evaluation of a novel magnetic nanocomposite with iron oxide deposited on cellulose nanofibers with nickel (Fe3O4@NFC@ONSM-Ni)

A heterogeneous, magnetically recoverable nanocomposite, Fe₃O₄@NFC@ONSM-Ni(ii) was prepared by immobilization of a novel Ni(ii) Schiff base complex on Fe₃O₄@NFC nanoparticles followed by treatment with melamine. This trinuclear catalyst has been characterized using several analytical techniques including FT-IR, TEM, Fe-SEM, EDX, DLS, ICP, TGA, VSM, and XRD. It was used as an efficient catalyst for one-pot solvent-free synthesis of 1,4-dihydropyridine and poly-hydro quinoline derivatives through Hantzsch reaction. This catalyst showed remarkable advantage over previously reported catalysts due to suitable conditions, short reaction time, high efficiency and lower catalyst load and timely recovery of the magnetic catalyst. Moreover, the effects of Fe₃O₄@NFC@ONSM-Ni(ii) nanoparticles on the in vitro proliferation of human leukemia cell line (k562) and human breast cancer cells (MDA-MB-231) were investigated. The results of MTT and Hochest assays suggested that the nanoparticles could effectively inhibit the proliferation of these cancer cells in a time- and concentration-dependent manner.

A heterogeneous, magnetically recoverable nanocomposite, Fe₃O₄@NFC@ONSM-Ni(ii) was prepared by immobilization of a novel Ni(ii) Schiff base complex on Fe₃O₄@NFC nanoparticles followed by treatment with melamine.     

Robust,highly active,and stable supported Co(ii) nanoparticles on magnetic cellulose nanofiber-functionalized for the multi-component reactions of piperidines and alcohol oxidation

The new recyclable cobalt three-core magnetic catalyst obtained by anchoring a Schiff base ligand sector and cellulose nanofiber slings on MNP (Fe₃O₄) was prepared and named as MNP@CNF@ATSM–Co(ii). Separately, MNPs and CNF have adsorbent properties of great interest. In this way, this catalyst was designed to synthesize piperidine derivatives under solvent-free conditions and alcohol oxidation reactions in EtOH as the solvent. It should be noted that this catalyst is environmentally safe and does not need an external base. This MNPs@CNF@ATSM–Co(ii) separable catalyst has been evaluated using various characterization techniques such as FT-IR, XRD, FE-SEM, EDX, EDS, ICP, TGA, DLS, HRTEM, and VSM. The catalyst was compatible with a variety of benzyl alcohols, benzaldehydes, and amines derivatives, and gave complimentary coupling products with sufficient interest for all of them. The synergistic performance of Co (trinuclear) in the catalyst was demonstrated and its different homologs such as MNPs, MNPs@CNF, MNPs@CNF@ATS–Co(ii), and MNPs@CNF@ATSM–Co(ii) were separately synthesized and applied to a model reaction, and then their catalytic activity was investigated. Also, the performance of these components for the oxidation reaction of alcohols was evaluated. The advantages of the current protocol include the use of a sustainable and safe low temperature, eco-friendly solvent no additive, and long-term stability and magnetic recyclability of the catalyst for at least five successive runs, thus following green chemistry principles. This protocol is a benign and environment-friendly method for oxidation and heterocycle synthesis. This powerful super-magnetic catalyst can use its three arms to advance the reactions, displaying its power for multi-component reactions and oxidation.

The new recyclable cobalt three-core magnetic catalyst obtained by anchoring a Schiff base ligand sector and cellulose nanofiber slings on MNP (Fe₃O₄) was prepared and named as MNP@CNF@ATSM–Co(ii).     

Cu(ii)-alginate-based superporous hydrogel catalyst for click chemistry azide–alkyne cycloaddition type reactions in water

A novel sustainable hydrogel catalyst based on the reaction of sodium alginate naturally extracted from brown algae Laminaria digitata residue with copper(ii) was prepared as spherical beads, namely Cu(ii)-alginate hydrogel (Cu(ii)-AHG). The morphology and structural characteristics of these beads were elucidated by different techniques such as SEM, EDX, BET, FTIR and TGA analysis. Cu(ii)-AHG and its dried form, namely Cu(ii)-alginate (Cu(ii)-AD), are relatively uniform with an average pore ranging from 200 nm to more than 20 μm. These superporous structure beads were employed for the copper catalyzed [3 + 2] cycloaddition reaction of aryl azides and terminal aryl alkynes (CuAAC) via click chemistry at low catalyst loading, using water as a solvent at room temperature and pressure. The catalytic active copper(i) species was generated by the reduction of copper(ii) by terminal alkyne via the oxidative alkyne homocoupling reaction. The prepared catalysts were found to be efficient (85–92%) and regioselective by affording only 1,4-disubstituted-1,2,3-triazoles. They were also recoverable and reused in their dried form for at least four consecutive times without a clear loss of efficiency. A mechanistic study was performed through density functional theory (DFT) calculations in order to explain the regioselectivity outcome of Cu(ii)-alginate in CuAAC reactions. The analysis of the local electrophilicity (ω_k) at the electrophilic reagent and the local nucleophilicity (N_k) at the nucleophilic confirms the polar character of CuAAC. This catalyst has the main advantage of being sustainably ligand-free and recyclable.

The Cu(ii)-alginate-based superporous hydrogel was prepared and used as a heterogenous catalyst in the regioselective click of 1,4-disubstituted-1,2,3-triazoles by CuAAC reactions.     

Fe3O4@nano-cellulose/Cu(ii): a bio-based and magnetically recoverable nano-catalyst for the synthesis of 4H-pyrimido[2,1-b]benzothiazole derivatives

Fe₃O₄@nano-cellulose/Cu(ii) as a green bio-based magnetic catalyst was prepared through in situ co-precipitation of Fe²⁺ and Fe³⁺ ions in an aqueous suspension of nano-cellulose. The mentioned magnetically heterogeneous catalyst was characterized by FT-IR, XRD, VSM, FESEM, TEM, XRF, EDS and TGA. In this research, the synthesis of 4H-pyrimido[2,1-b]benzothiazole derivatives was developed via a three component reaction of aromatic aldehyde, 2-aminobenzothiazole and ethyl acetoacetate using Fe₃O₄@nano-cellulose/Cu(ii) under solvent-free condition at 80 °C. Some advantages of this protocol are good yields, environmentally benign, easy work-up and moderate reusability of the catalyst. The product structures were confirmed by FT-IR, ¹H NMR, and ¹³C NMR spectra.

Fe₃O₄@nano-cellulose/Cu(ii) as a green bio-based magnetic catalyst are prepared, characterized and applied for synthesis of 4H-pyrimido[2,1-b]benzothiazoles with good to excellent yields.     

Extraction and preconcentration of Ni(ii), Pb(ii), and Cd(ii) ions using a nanocomposite of the type Fe3O4@SiO2@polypyrrole-polyaniline

In this study, the application of Fe₃O₄@SiO₂@polypyrrole-polyaniline magnetic nanocomposite was studied for Ni(ii), Cd(ii), and Pb(ii) ions preconcentration extraction. In this regard, the silica layer prevents the Fe₃O₄ nanoparticles (NPs) from aggregating over a broad pH range value and simultaneously improves chemical stability and hydrophilicity. By using a Box–Behnken design, the effect of various parameters affecting the preconcentration was studied. FAAS was employed to quantify the eluted analytes. The detection limits are 0.09, 1.1, and 0.3 ng mL⁻¹ for Ni(ii), Cd(ii) and Pb(ii), ions, respectively. The relative standard deviations (RSDs%) were calculated for determining the method''s precision, lower than 7.5%. The capacities of sorption are 75, 84, and 98 mg g⁻¹, respectively. With the usage of a certified reference material, the developed method was validated. After that, the validated method was employed to rapidly extract trace target ions from food samples and gave satisfactory results.

In this study, the application of Fe₃O₄@SiO₂@polypyrrole-polyaniline magnetic nanocomposite was studied for Ni(ii), Cd(ii), and Pb(ii) ions preconcentration extraction.     

Theoretical study of ternary silver fluorides AgMF4 (M = Cu,Ni, Co) formation at pressures up to 20 GPa

Only several compounds bearing the Ag(ii) cation and other paramagnetic transition metal cations are known experimentally. Herein, we predict in silico stability and crystal structures of hypothetical ternary silver(ii) fluorides with copper, nickel and cobalt in 1 : 1 stoichiometry at a pressure range from 0 GPa up to 20 GPa employing the evolutionary algorithm in combination with DFT calculations. The calculations show that AgCoF₄ could be synthesized already at ambient conditions but this compound would host diamagnetic Ag(i) and high-spin Co(iii). Although none of the compounds bearing Ag(ii) could be preferred over binary substrates at ambient conditions, at increased pressure ternary fluorides of Ag(ii) featuring Cu(ii) and Ni(ii) could be synthesized, in the pressure windows of 7–14 and 8–15 GPa, respectively. All title compounds would be semiconducting and demonstrate magnetic ordering. Compounds featuring Ni(ii) and particularly Co(ii) should exhibit fundamental band gaps much reduced with respect to pristine AgF₂. The presence of Cu(ii) and Ni(ii) does not lead to electronic doping to AgF₂ layers, while Co(ii) tends to reduce Ag(ii) entirely to Ag(i).

Only several compounds bearing the Ag(ii) cation and other paramagnetic transition metal cations are known experimentally. Here, we predict as yet unknown AgMF₄ phases and their stability in function of pressure.     

Functionalized biochar-supported magnetic MnFe2O4 nanocomposite for the removal of Pb(ii) and Cd(ii)

In this study, a novel magnetic biochar-MnFe₂O₄ nanocomposite (BC/FM) was prepared using low-cost corn straw and MnFe₂O₄ by sol–gel/pyrolyzing route using egg white, which has abundant functional groups (–NH₂ and –COOH). Following that, its composition, morphology and structure was characterized by various techniques including SEM-EDX, BET, XRD, and VSM. Batch experiment of the adsorption for Pb(ii) and Cd(ii) including influence of pH, kinetics, isotherm and thermodynamics was also studied. The results demonstrated that biochar could effectively support MnFe₂O₄, which displayed high dispersion on the surface of the biochar and possessed abundant functional groups and high surface area contributing to superior performance on Pb(ii) and Cd(ii) removal. Therein, MnFe₂O₄ with high magnetism is convenient for separating the magnetic BC/FM from an aqueous medium. Adsorption experiment results indicate that Pb(ii) and Cd(ii) removal by BC/FM was closely related to pH with the best value of pH 5.0, and the process reached equilibrium in 2 h. The adsorption process is well-described by the pseudo-second-order kinetic model and Sips (Freundlich–Langmuir) model. Thermodynamic studies suggest that the adsorption process is spontaneous and exothermic. The maximum experimental adsorption capacity of BC/FM is 154.94 and 127.83 mg g⁻¹ for Pb(ii) and Cd(ii), respectively, in single-solute system, which is higher than that of some of the other adsorbents of biochar or biochar-based composites. In bi-solute system, the preferential adsorption order of BC/FM for the two metals is Pb(ii) prior to Cd(ii). Finally, FTIR and XPS analysis verified that the main mechanism of Pb(ii) and Cd(ii) removal by BC/FM is by forming Pb/Cd–O or complexation of carboxyl and hydroxyl and ion exchange. Therefore, the prepared magnetic BC/FM composite, as an excellent adsorbent, exhibited potential applications for the removal of Pb(ii) and Cd(ii) from wastewater.

In this study, a novel magnetic biochar-MnFe₂O₄ nanocomposite (BC/FM) was prepared using low-cost corn straw and MnFe₂O₄ by sol–gel/pyrolyzing route using egg white, which has abundant functional groups (–NH₂ and –COOH).     

An investigation of two copper(ii) complexes with a triazole derivative as a ligand: magnetic and catalytic properties

Two new copper(ii) complexes [Cu₂(L)₂(OAc)₂(H₂O)₂] (1) (L = 3-methyl-5-pyridin-2-yl-1,2,4-triazole) and [CuL₂] (2) were prerared and thoroughly studied. The complexes are able to selectively catalyze the oxidation of styrene towards benzaldehyde and of cyclohexane to KA oil. The 2D coordination polymer 1 showed an antiferromagnetic behaviour attributed to the intrachain magnetic coupling.

Two copper(ii) complexes were investigated as catalysts for selective oxidation of styrene to benzaldehyde and of cyclohexane to KA oil.     

High Tm linear poly(l-lactide)s prepared via alcohol-initiated ROPs of l-lactide

Alcohol-initiated ROPs of l-lactide were performed in bulk at 160 °C for 72 h with variation of the catalyst or with variation of the initiator (aliphatic alcohols). Spontaneous crystallization was only observed when cyclic Sn(ii) compounds were used as a catalyst. Regardless of initiator, high melting crystallites with melting temperatures (T_m) of 189–193 °C were obtained in almost all experiments with Sn(ii) 2,2′-dioxybiphenyl (SnBiph) as catalyst, even when the time was shortened to 24 h. These HT_m poly(lactide)s represent the thermodynamically most stable form of poly(l-lactide). Regardless of the reaction conditions, such high melting crystallites were never obtained when Sn(ii) 2-ethylhexanoate (SnOct₂) was used as catalyst. SAXS measurements evidenced that formation of HT_m poly(l-lactide) involves growth of the crystallite thickness, but chemical modification of the crystallite surface (smoothing) seems to be of greater importance. A hypothesis, why the “surface smoothing” is more effective for crystallites of linear chains than for crystallites composed of cycles is discussed.

By variation of reaction conditions and catalysts a cyclic tin(ii) compound was found, which enables synthesis of high melting (>190 °C) poly(l-lactide) via ROP of l-lactide, whereas the technically used catalyst SnOct₂ does not show such a performance.     

Simultaneous removal of Sb(iii) and Cd(ii) in water by adsorption onto a MnFe2O4–biochar nanocomposite

In this study, a jacobsite–biochar nanocomposite (MnFe₂O₄–BC) was fabricated and used to simultaneously remove Sb(iii) and Cd(ii) from water via adsorption. The MnFe₂O₄–BC nanocomposite was prepared via a co-precipitation method and analyzed using various techniques. The results confirm the successful decoration of the biochar surface with MnFe₂O₄ nanoparticles. The maximum Sb(iii) removal efficiency was found to be higher from bi-solute solutions containing Cd(ii) than from single-solute systems, suggesting that the presence of Cd(ii) enhances the removal of Sb(iii). The Langmuir isotherm model describes well Sb(iii) and Cd(ii) removal via adsorption onto the MnFe₂O₄–BC nanocomposite. The maximum adsorption capacities are 237.53 and 181.49 mg g⁻¹ for Sb(iii) and Cd(ii), respectively, in a bi-solute system. Thus, the prepared MnFe₂O₄–BC nanocomposite is demonstrated to be a potential adsorbent for simultaneously removing Sb(iii) and Cd(ii) ions from aqueous solutions.

In this study, a jacobsite–biochar nanocomposite (MnFe₂O₄–BC) was fabricated and used to simultaneously remove Sb(iii) and Cd(ii) from water via adsorption.     

Selective oxidation of alcohols and sulfides via O2 using a Co(ii) salen complex catalyst immobilized on KCC-1: synthesis and kinetic study

The aim of this study was to immobilize a Co(ii) salen complex on KCC-1 as a catalyst that can be recovered (Co(ii) salen complex@KCC-1). Field-emission transmission electron microscopy, FT-IR spectroscopy, thermogravimetric analysis, elemental analysis, atomic absorption spectroscopy, and XRD were used to confirm the structure and chemical nature of Co(ii) salen complex@KCC-1. The oxidation efficiency was obtained for an extensive range of sulfides and alcohols using this sustainable catalyst, alongside O₂ as an oxygen source and isobutyraldehyde (IBA) as an oxygen acceptor, with superior selectivity and conversion for the relevant oxidation products (sulfoxides and ketones or aldehydes) under moderate conditions. The μ-oxo and peroxo groups on the ligands of the Co complex appeared to be responsible for the superior activity of the catalyst. Essential factors behind the oxidation of alcohol and sulfoxides were investigated, including the catalyst, solvent, and temperature. In this paper, molecular oxygen (O₂) was used as a green oxidant. Furthermore, kinetic studies were conducted, revealing a first-order reaction for the oxidation of both benzyl alcohol and sulfide. The reaction progressed at mild temperature, and the catalyst could be easily recovered and reused for numerous consecutive runs under the reaction conditions, without any substantial reduction in the functionality of the catalytic system.

The aim of this study was to immobilize a Co(ii) salen complex on KCC-1 as a catalyst that can be recovered (Co(ii) salen complex@KCC-1).     

A multifunctional composite Fe3O4/MOF/l-cysteine for removal,magnetic solid phase extraction and fluorescence sensing of Cd(ii)

Fe₃O₄/MOF (metal organic framework)/l-cysteine was synthesized and applied for the removal of Cd(ii) from wastewater. The adsorption kinetics and isotherms were investigated, and the results indicated that the adsorption obeyed the pseudo-second-order kinetic model and Langmuir isotherm. The maximum adsorption capacity was calculated to be 248.24 mg g⁻¹. Fe₃O₄/MOF/l-cysteine was further applied to determine trace amounts of Cd(ii) in real water samples using ICP-AES (inductively coupled plasma-atomic emission spectroscopy) based on magnetic solid-phase extraction (MSPE). The determination limit was 10.6 ng mL⁻¹. Additionally, Fe₃O₄/MOF/l-cysteine can also be used as a fluorescent sensor for “turn-off” detection of Cd(ii), and the detection limit was 0.94 ng mL⁻¹.

Fe₃O₄/MOF (metal organic framework)/l-cysteine was synthesized and applied for the removal of Cd(ii) from wastewater.     

Single molecule magnets of cobalt and zinc homo- and heterometallic coordination polymers prepared by a one-step synthetic procedure

The synthesis of 1D cobalt and zinc monometallic and heterometallic coordination polymers (CPs) was carried out applying one-pot synthetic methods by using either supercritical carbon dioxide or ethanol as the solvent. A collection of four 1D CPs were thus obtained by the combination of a metal (or a mixture of metals) with the linker 1,4-bis(4-pyridylmethyl)benzene. The used metallic complexes were zinc and cobalt hexafluoroacetylacetonate, which can easily incorporate pyridine ligands in the coordination sphere of the metal centre. Independently of the used solvent, the precipitated phases involving Zn(ii), i.e., homometallic CP of Zn(ii) and bimetallic CP of Zn(ii)/Co(ii), were isostructural. Contrarily, homometallic CPs of Co(ii) were precipitated as an isostructural phase of Zn(ii) or with a different structure, depending on the used solvent. All the structures were resolved by XRD using synchrotron radiation. In addition, the magnetic properties of the new CPs involving Co(ii) were studied. Remarkably, at low temperatures with the application of an external field, they acted as field-induced single molecule magnets.

One-pot synthesis of heterometallic (Zn(ii)/Co(ii)) nodes directing CP magnetic behaviour to single molecule magnets.     

Efficient reduction of nitro compounds and domino preparation of 1-substituted-1H-1,2,3,4-tetrazoles by Pd(ii)-polysalophen coated magnetite NPs as a robust versatile nanocomposite

A new, versatile, and green methodology has been developed for the efficient NaBH₄-reduction of nitroarenes as well as the domino/reduction MCR preparation of 1-substituted-1H-1,2,3,4-tetrazoles using Pd(ii)-polysalophen coated magnetite NPs as an efficient heterogeneous magnetically recyclable nanocatalyst. Polysalophen was firstly prepared based on a triazine framework with a high degree of polymerization, then coordinated to Pd ions and, finally, the resulting hybrid was immobilized on magnetite NPs. The catalyst was characterized by various instrumental and analytical methods, including GPC, DLS, N₂ adsorption–desorption, TGA, VSM, TEM, HRTEM, EDX, XPS, XRD, and ICP analyses. The catalyst possesses dual-functionality including the reduction of nitroarenes and the construction of tetrazole rings all in one step via a domino protocol. High to excellent yields were obtained for both nitro reduction and the direct preparation of 1-substituted-1H-1,2,3,4-tetrazoles from nitro compounds. Insight into the mechanism was conducted by XPS in situ as well as DLS in situ along with several control experiments. Recyclability of the catalyst was studied for 6 consecutive runs along with metal leaching measurements in each cycle.

Facile nitroarene reduction as well as domino/reduction MCR preparation of 1-substituted-1H-1,2,3,4-tetrazoles from nitroarenes was performed by Pd(ii)-polysalophen coated magnetite NPs as a highly selective, recyclable and efficient nanocomposite.     

Synthesis of Cu2O–CuFe2O4 microparticles from Fenton sludge and its application in the Fenton process: the key role of Cu2O in the catalytic degradation of phenol

This paper presents the key role of Cu₂O in Fenton catalysis using Cu₂O–CuFe₂O₄ magnetic microparticles, which were prepared using Fenton sludge as an iron source. The catalytic activity of the as-prepared Cu₂O–CuFe₂O₄ and CuFe₂O₄ microparticles was evaluated in a heterogeneous Fenton system for the degradation of recalcitrant phenol. The Cu₂O–CuFe₂O₄ microparticles demonstrated relatively superior catalytic performance as compared to CuFe₂O₄ microparticles when used as a Fenton catalyst. The relatively higher catalytic activity of Cu₂O–CuFe₂O₄ for phenol degradation during the Fenton process could be attributed to the availability of both monovalent [Cu(i)] and divalent [Cu(ii)] as well as Fe(ii)/Fe(iii) redox pairs, which could react quickly with H₂O₂ to generate hydroxyl radicals (HO˙). An electron bridge was formed between Cu(i) and Fe(iii), which accelerates the formation of Fe(ii) species in order to boost the reaction rate. Highly reactive and excessively available Cu(i) species for as prepared Cu₂O–CuFe₂O₄ microparticles could be considered to be rather crucial for the generation of highly reactive HO˙ radical species. In addition, the as-prepared Cu₂O–CuFe₂O₄ magnetic microparticles exhibited sound stability and reusability.

The higher catalytic activity of Cu₂O–CuFe₂O₄ could be attributed to the availability of both Cu(i) and Cu(ii) as well as Fe(ii)/Fe(iii).     

Lead and uranium sorptive removal from aqueous solution using magnetic and nonmagnetic fast pyrolysis rice husk biochars

This paper discusses the sorption characteristics of Pb(ii) and U(vi) on magnetic and nonmagnetic rice husk biochars. The porosity, specific surface area, hydrophobility, and reusability of biochar were effectively improved (1–2 times) after magnetic modification. The optimum adsorption conditions were as follows: biochar loading was 0.4 g L⁻¹, pH value was 7.0, and anion strength of NO₃⁻ and PO₄³⁻ were 0.01 mol L⁻¹ for Pb(ii) and 0.04 mol L⁻¹ for U(vi) respectively. Compared with U(vi), Pb(ii) had the faster adsorption rate and higher adsorption capacity on magnetic biochar (MBC). The adsorption experimental data were well fitted by pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity of Pb(ii) and U(vi) on MBC was 129 and 118 mg g⁻¹ at 328 K respectively, which was significantly higher than that of other sources biochars. Pb(ii) was mainly bonded to biochar by physisorption but the adsorption of U(vi) on biochar was mostly chemisorption. Fe oxides in MBC noticeably improved the ion exchange and complexation action between biochar and metal ion especially for U(vi). The experimental results confirmed MBC material can be used as a cost-effective adsorbent for the removal of Pb(ii) and U(vi) and can be separated easily from aqueous solution when application.

This paper discusses the sorption characteristics of Pb(ii) and U(vi) on magnetic and nonmagnetic rice husk biochars.     

Photoaccelerated energy transfer catalysis of the Suzuki–Miyaura coupling through ligand regulation on Ir(iii)–Pd(ii) bimetallic complexes

Three bimetallic Ir(iii)–Pd(ii) complexes [Ir(ppy)₂(bpm)PdCl₂](PF₆) (ppy = 2-phenylpyridine, 1), [Ir(dfppy)₂(bpm)PdCl₂](PF₆) (dfppy = (4,6-difluorophenyl)pyridine, 2), and [Ir(pq)₂(bpm)PdCl₂](PF₆) (pq = 2-phenylquinoline, 3) were synthesized by using 2,2′-bipyrimidine (bpm) as a bridging ligand. The influences of the cyclometalated ligand at the Ir(iii) center on the photophysical and electrochemical properties as well as photocatalytic activity for the Suzuki–Miyaura coupling reaction under mild conditions were evaluated. The results revealed that complex 3 enables dramatically accelerating the Suzuki–Miyaura coupling reaction under visible light irradiation at room temperature, due to the effective absorption of visible light and appropriate locus of the excited chromophore. Mechanism studies showed that the chromophore [Ir(pq)₂(bpm)] fragment absorbs visible light to produce the triplet excited state centering on the bridging ligand which boosts the formation of electron rich Pd(ii) units and facilitates the oxidative addition step of the catalytic cycle. Simultaneously, the excited chromophore undergoes energy transfer efficiently to the Pd(ii) reaction site to form the excited Pd(ii) species, resulting in enhancement of Pd(ii) reduction steps of the Suzuki–Miyaura coupling reaction and increasing the reactivity of the catalyst. This provides a new strategy for designing photocatalysts for coupling reaction through altering the cyclometalated ligand to modulate the photophysical properties and the cooperation between two metal units.

A series bimetallic catalysts were synthesized. Relationship between the structure of catalysts and catalytic reactivities were studied and improvement of the catalytic efficiency for Suzuki–Miyaura coupling was accomplished by regulating their chromophores.     

Synthesis and characterization of a surface-grafted Pb(ii)-imprinted polymer based on activated carbon for selective separation and pre-concentration of Pb(ii) ions from environmental water samples

Even the lowest concentration level of lead (Pb) in the human body is dangerous to health due to its bioaccumulation and high toxicity. Therefore, it is very important to develop selective and fast adsorption methods for the removal of Pb(ii) from various samples. In this paper, a new Pb(ii) ion-imprinted polymer (Pb(ii)-IIP) was prepared with surface imprinting technology by using lead nitrate as a template, for the solid-phase extraction of trace Pb(ii) ions in environmental water samples. The imprinted polymer was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and N₂ adsorption–desorption isotherms. The separation/pre-concentration conditions for Pb(ii) were investigated, including the effects of pH, shaking time, sample flow rate, elution conditions and interfering ions. Compared with non-imprinted particles, the ion-imprinted polymer had a higher selectivity and adsorption capacity for Pb(ii). The pseudo-second-order kinetics model and Langmuir isotherm model fitted well with the adsorption data. The relative selectivity factor values (α_r) of Pb(ii)/Zn(ii), Pb(ii)/Ni(ii), Pb(ii)/Co(ii) and Pb(ii)/Cu(ii) were 168.20, 192.71, 126.13 and 229.39, respectively, which were all much greater than 1. The prepared Pb(ii)-imprinted polymer was shown to be promising for the separation/pre-concentration of trace Pb(ii) from natural water samples. The adsorption and desorption mechanisms were also proposed.

Even the lowest concentration level of lead (Pb) in the human body is dangerous to health due to its bioaccumulation and high toxicity.     

Novel tetrahedral cobalt(ii) silanethiolates: structures and magnetism

Three heteroleptic complexes of Co(ii) tri-tert-butoxysilanethiolates have been synthesized with piperidine [Co{SSi(OtBu)₃}₂(ppd)₂] 1, piperazine [Co{SSi(OtBu)₃}₂(NH₃)]₂(μ-ppz)·2CH₃CN 2, and N-ethylimidazole [Co{SSi(OtBu)₃}₂(etim)₂] 3. The complexes have been characterized by a single-crystal X-ray, revealing their tetrahedral geometry on Co(ii) coordinated by two nitrogen and two sulfur atoms. Complexes 1 and 3 are mononuclear, whereas 2 is binuclear. The spectral properties and thermal properties of 1–3 complexes were established by FTIR spectroscopy for solid samples and TGA. The magnetic properties of complexes 1, 2, and 3 have been investigated by static magnetic measurements and X-band EPR spectroscopy. These studies have shown that 1 and 3, regardless of the similarity in structure of CoN₂S₂ cores, demonstrate different types of local magnetic anisotropy. Magnetic investigations of 2 reveal the presence of weak antiferromagnetic intra-molecular Co(ii)–Co(ii) interactions that are strongly influenced by the local magnetic anisotropy of individual Co(ii) ions.

Structural, spectral and thermal properties of three tetrahedral Co(ii) silanethiolates were established by XRD, FTIR for solid samples and TGA. The magnetic properties were investigated by static magnetic measurements and X-band EPR spectroscopy.