Tin-derivative sandwich-type polyoxometalates supported on Nd-doped TiO2 nanoparticles as efficient and reusable catalysts in the oxidation of sulfides and alcohols

New nanocomposites, including different loading levels of sandwich-type polyoxometalates [(HOSn^IVOH)₃(XW₉O₃₄)₂]^n? (X = As (1), P (2) n = 12 and Si (3) n = 14) on Nd-doped TiO₂ nanoparticles were prepared by a simple impregnation method. The nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, Fourier transform infrared (FTIR), and energy-dispersive X-ray spectroscopy. Compounds 1–3 were successfully loaded on Nd-doped crystallized anatase-phase TiO₂ nanoparticles of 20–25 nm. Catalytic activities of nanocomposites were examined by carrying out the oxidation of sulfides and alcohols with H₂O₂. Simple synthesis method, reusability, and low amounts of the heterogeneous catalysts with a slight excess of H₂O₂ and mild reaction conditions make these oxidation reactions an environmentally benign chemical process.     

Voltammetric Study of the Influence of Various Phosphate Anions on Silver Nanoparticle Oxidation

The antibacterial properties of silver are strongly controlled by the redox couple of silver/silver(I). This work reports the influence of phosphate anions on silver nanoparticle oxidation, which is important given the abundance of phosphate species in biological systems. The three different species of anions were found to have a varying degree of influence on silver oxidation with the order PO₄³⁻>HPO₄²⁻>H₂PO₄⁻. It was found that in the presence of phosphate anions, the silver oxidation potential shifts to a less positive value, which indicated the increasing ease of the oxidation reaction of silver. Given that the interplay between silver and its cation is crucial to its antibacterial properties and significant concentrations of the HPO₄²⁻ anion are present at biological pH (near neutral), it is essential that the influence of the dibasic anion (HPO₄²⁻) on silver oxidation dynamics be considered for biological systems.     

Exploring the Interactions of Atomic Oxygen on Silver Clusters with Hydrogen

The interactions between Ag_nO^-(n=1-8) and H₂ (or D₂) were explored by combination of the mass spectroscopy experiments and density function theory (DFT) calculations. The experiments found that all oxygen atoms in Ag_nO^-(n=1-8) are inert in the interactions with H₂ or D₂ at the low temperature of 150 K, which is in contrast to their high reactivity with CO under the same condition. These observations are parallel with the preferential oxidation (PROX) of CO in excess hydrogen catalyzed by dispersed silver species in the condensed phase. Possible reaction paths between Ag_nO^-(n=1-8) and H₂ were explored using DFT calculations. The results indicated that adsorption of H₂ on any site of Ag_nO^-(n=1-8) is extremely weak, and oxidation of H₂ by any kind of oxygen in Ag_nO^-(n=1-8) has an apparent barrier strongly dependent on the adsorption style of the "O". These experiments and theoretical results about cluster reactions provided molecule-level insights into the activity of atomic oxygen on real silver catalysts.     

Catalytic effect of iron(III) on the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone by hydrogen peroxide : Kinetic Fluorimetric Determination of Iron

A kinetic method is described for the determination of nanogram amounts of iron(III) based on its catalysis of the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone by hydrogen peroxide in an ammoniacal medium. In order to monitor the reaction, the appearance rate of fluorescence of the oxidation product (λ_ex=365 nm, λ_em=440 nm) is measured. The calibration graph is linear in the range 10–60 ng ml^?1 iron(III) with an r.s.d, of ± 1.3%. The proposed method has few interferences and has been applied satisfactorily to the determination of iron in several alloys and minerals. A mechanism for the catalyzed reaction is proposed.     

The reduction process of phytic acid–silver ion system: A pulse radiolysis study

Reduction of silver ion in a silver–phytic acid (1:1 ratio) system has been studied using pulse radiolysis technique. Time-resolved transformation of the intermediates, Ag⁺→Ag⁰→Ag₂⁺→Ag₃²⁺, has been clearly observed in the reduction of silver–phytic acid (1:1) system. The effect of phytic acid on the formation and decay of initial silver clusters has been also studied. The surface plasmon absorption band of stable silver nanoparticle (410 nm) and dynamic light scattering technique has been used to characterize the nanoparticles and measure the average size (R_av=100 nm).     

Synthesis,characterization, and antimicrobial activity of two Schiff base silver(I) complexes derived from 4-carboxybenzaldehyde

Two new Schiff base silver(I) complexes, {[Ag(L¹)][H₂O]}_∞ (1) and {[Ag(L²)][H₂O]}_∞ (2), where L¹ = 4-((2-diethylaminoethylimino)methyl)phenecarboxylate and L² = 4-([3-(morpholin-4-yl)propyl]iminomethyl)phenecarboxylate, have been synthesized and characterized. X-ray crystallographic analysis reveals that silver ions in 1 are bridged by L¹ to form a one-dimensional zigzag chain, while three silver ions in 2 are linked by L² to produce a two-dimensional coordination polymer. Guest water molecules in 1 generate a one-dimensional hydrogen-bonded chain. Both 1 and 2 offer high antibacterial activity against Gram-positive bacteria Staphylococcus aureus with MIC values of 0.26 and 0.24 mM and to exhibit good inhibitory activity against urease with the respective IC₅₀ values of 3.5 ± 0.1 and 3.8 ± 0.2 μM.     

Synthesis,crystal structure,thermal stability,and photoluminescence of a 3-D silver(I) network with twofold interpenetrated dia-f topology

A silver(I) coordination polymer with mixed 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (bpz) and maleic acid, [Ag₂(bpz)₃(fum)]_n (1, H₂fum = fumaric acid), was synthesized under hydrothermal condition by in situ isomerization of maleic acid to fumaric acid and characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction, TGA, and single-crystal X-ray diffraction. The maleic acid in situ isomerizes to fumaric acid and participates in the formation of 1. Topologically, the structure of 1 features a rare 3-connected twofold interpenetrated dia-f net with a point symbol of {4.14²}. Compound 1 exhibits photoluminescence in the solid state with an emission maximum at 470 nm upon excitation at 365 nm at room temperature, which is attributed to intraligand or/and interligand π → π* transition.     

Reversible oxidation/reduction of silver supported on silica aerogel: Influence of the addition of phosphate

Ag/SiO₂ and Ag₃PO₄/SiO₂ systems supported on silica aerogel were investigated using temperature-programmed reduction (TPR), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and infrared spectroscopy. The formation of highly dispersed silver particles, uniformly distributed along the surface and stabilized with silanol groups, was observed for Ag/SiO₂ system. Phosphate and silanol groups produce two states of silver localization in phosphate-containing system. The addition of phosphate onto the silica surface leads to the reversible oxidation/reduction of silver in the temperature range of 100–300°C with transitions of silver (particles 10–30 nm in size) to charged states (ions, clusters stabilized by phosphate groups). This reversible behavior of silver is stable, and the amount of silver involved in these processes remained constant (∼50%) for the series of consistent cyclic oxidation/reduction treatments.     

基于苯四甲酸和双(咪唑基甲基)苯配体的三维Cd-MOF的合成、结构及荧光性质

选择刚性的1,2,4,5-均苯四甲酸(H4L)为主配体,以1,3-双(1H-咪唑-1-基甲基)苯(1,3-bib)为辅助配体,在水热条件下,与过渡金属离子Cd2+配位合成了配合物[Cd(L)0.5(1,3-bib)(H2O)]·H2O (1).利用元素分析、红外光谱、X射线单晶衍射、热重和X射线粉末衍射对其结构进行了表...     

The Catalytic Cycle of Oxidation of Iodide Ion in the Oxygen/Nitrous Acid/Nitric Oxide System and Its Potential for Analytical Applications

Abstract

The oxidation of iodide to iodine by nitrous acid in aqueous acidic medium takes place catalytically in the presence of dissolved oxygen and can be followed spectrophotometrically at 288 and 352 nm. An indirect molar absorptivity for nitrite on the basis of I₃ ^? formation can be as high as 8.5×10⁵ L mol^?1 cm^?1 at 288 nm. Analytical curves were established. The iodine released in the catalytic cycle can also be titrated with thiosulfate. The reaction is pseudo–second‐order in oxygen consumed, with t_1/2=15.7 min at 25°C. A rate determining step could be the NO · O₂ as the activated species. Measurements of the iodine formed at catalytic conditions was used to determine nitrite in meat extracts and NOx in car exhausts.     

Design and characterization of silver(I) azide coordination polymers based on 1,2-bis(4-pyridyl)ethane and phenazine

Two silver(I) azide supramolecular coordination polymers (SCPs) with N-donor ligands have been synthesized and structurally characterized by physicochemical and spectroscopic methods; [AgN₃.bpe] where bpe = 1,2-bis(4-pyridyl)ethane, 1, and [(AgN₃)₂.phenz], 2, where phenz = phenazine. Syntheses were carried out in H₂O/acetonitrile/NH₃ media at room temperature. The topology of the bipodal ligands directs the silver azide building blocks to adopt different structures; 1D-chain, 1, or 1D-ribbon, 2. The azide groups exhibit an unusual bent structure with increasing bridging capability to adopt enough space for the bipodal ligands. The structure of SCP 2 contains the cyclic motif {Ag₂(μ₃-N₃)₂} to accommodate the voluminous phenz ligand. The emission spectra of the SCPs 1 and 2 display emission bands at 400–650 nm.     

以N, N’-二异丁基-2, 3-二胺基喹喔啉为配体的钴和锌配合物的合成、晶体结构以及性质研究

本文以2,3-二氯喹喔啉和异丁胺为原料,合成了N,N’-二异丁基-2,3二胺基喹喔啉（L）,并合成了两个标题配合物（[Co（DIDAQX）Cl₂]）（1,DIDAQX=N,N’-Diisobutyl-2,3-（1H,4H）-diaminoquinoxaline）和（[Zn（DIDAQX）Cl₂]）（2）。并对其进行了红外、元素分析、单晶衍射、热重、荧光、电化学性质等性质研究。且对1做了密度泛函理论（DFT）计算。单晶结构分析表明1和2同构,都属于正交晶系,Pbca空间群,1的晶胞参数：a=1.4082（3）nm,b=1.4628（3）nm,c=1.7970（4）nm;V=3.7017（14）nm³,Z=8。2的晶胞参数：a=1.4082（3）nm,b=1.4648（3）nm,c=1.7969（4）nm;V=3.7065（14）nm³,Z=8。在配合物结构中每个金属原子以四配位的形式分别与2个Cl原子和来自配体的2个N原子配位,形成了一个扭曲的四面体结构。     

以N,N′-二异丁基-2,3-二胺基喹喔啉为配体的钴和锌配合物的合成、晶体结构以及性质研究(英文)

以2,3-二氯喹喔啉和异丁胺为原料,合成了N,N′-二异丁基-2,3二胺基喹喔啉(L),并合成了两个标题配合物([Co(DIDAQX)Cl2])(1,DIDAQX=N,N′-Diisobutyl-2,3-(1H,4H)-diaminoquinoxaline)和([Zn(DIDAQX)Cl2])(2)。并对其进行了红外、元素分析、单晶衍射、热重、荧光、电化学性质等性质研究。且对1做了密度泛函理论(DFT)计算。单晶结构分析表明1和2同构,都属于正交晶系,Pbca空间群,1的晶胞参数:a=1.408 2(3)nm,b=1.462 8(3)nm,c=1.797 0(4)nm;V=3.701 7(14)nm3,Z=8。2的晶胞参数:a=1.408 2(3)nm,b=1.464 8(3)nm,c=1.796 9(4)nm;V=3.706 5(14)nm3,Z=8。在配合物结构中每个金属原子以四配位的形式分别与2个Cl原子和来自配体的2个N原子配位,形成了一个扭曲的四面体结构。     

Synthesis,characterization, electrochemical and theoretical study of substituted phenyl-terpyridine and pyridine-quinoline based mixed chelate ruthenium complexes

In the present work, we report two methoxy-substituted phenyl-terpyridine ruthenium complexes with pyridine carboxyquinoline and NCS as ancillary ligands, [Ru(OMePhtpy)(pcqH)(NCS)](PF₆) (1) and [Ru(triOMePhtpy)(pcqH)(NCS)](PF₆) (2) (where OMePhtpy = (4′-(4-methoxy)phenyl-2,2′:6′,2″-terpyridine, triOMePhtpy = (4′-(3,4,5-trimethoxy)phenyl-2,2′:6′,2″-terpyridine and pcqH = pyridine-carboxyquinoline). Both complexes have been characterized by spectroscopic techniques e.g., mass, ¹H-NMR and FTIR. UV–vis spectrophotometric and electrochemical studies for both complexes have been performed. The substitution pattern of the –OMe groups have been successfully utilized to tune the redox potential of the metal complexes. On the anodic side of cyclic voltammogram, 1 and 2 show an irreversible wave corresponding to Ru^II/III couple at 0.95 and 0.85 V, respectively. The lower Ru^II/III oxidation potential for 2 may be attributed to increased electron density on ruthenium due to three (+R) methoxy–groups appended to the phenyl moiety of triOMePhtpy. DFT optimization of structure and energy calculation reveals that in both complexes, HOMO is metal- and thiocyanate-based, whereas the LUMO is based on pcqH. Correlation of TDDFT results with experimental electronic spectrum indicates that bands at 502 nm (1) and 528 nm (2) are of MLLCT character from ruthenium-thiocyanate to pcqH.     

Determination of Micro Amounts of Metallic Silver in Silver Salt Matrices

ABSTRACT

A spectrochemical method has been developed for the quantitative determination of metallic silver in silver nitrate and silver chloride or bromide matrices exposed to light. The method is based on the oxidation of silver(0) by iron(III) at pH 3.5 in the presence of ferrozine. The resulting absorbance of the iron ferrozine complex is measured at 562 nm. Less than 0.1 mg of metallic silver can be determined with a relative standard deviation better than 6%.     

以苯四甲酸和双(咪唑基甲基)苯为配体的三维Cd-MOF材料的合成、结构及荧光性质

选择刚性的1,2,4,5-均苯四甲酸（H₄L）为主配体,以1,3-双（1H-咪唑-1-基甲基）苯（1,3-bib）为辅助配体,在水热条件下,与过渡金属离子Cd²⁺配位合成了配合物[Cd（L）_0.5（1,3-bib）（H₂O）]·H₂O（1）。利用元素分析、红外光谱、X射线单晶衍射、热重和X射线粉末衍射对其结构进行了表征,并研究了化合物的荧光性质。结果表明：配合物1属正交晶系,空间群Pbca,a=0.857 08（4）nm,b=1.912 23（10）nm,c=2.451 60（12）nm。配合物1中Cd²⁺与L^4-配体的羧基通过双齿螯合配位,通过1,3-bib连接形成三维网状结构。配合物1具有较强的荧光,其对丙酮溶剂、MnO₄^-、Hg²⁺离子有一定的荧光猝灭。     

Kinetics of electrochemical reactions on the Ag(Hg)/Ag4RbI5 interface

The electrochemical behaviour of the Ag(Hg)/Ag₄RbI₅ interface is investigated by a potentiostatic pulse method. It is found that the rate-determining step of the electrode reaction is electron transfer with an exchange current density of 68 mA cm^–2 and a transfer coefficient of approximately 0.45. The order of the electrochemical reaction for silver oxidation is estimated from polarization investigations of silver amalgam in various concentrations. From this it is deduced that the mercury is ionized and is implanted in the electrolyte together with silver under anodic polarization: 15Ag+85Hg–100e^–→15Ag⁺+85Hg⁺. From comparison of the electrochemical behaviour of the Ag(Hg)/Ag₄RbI₅ and Ag/Ag₄RbI₅ interfaces it is concluded that the rate of anodic silver dissolution on the Ag/Ag₄RbI₅ interface is limited by crystallization effects. Electronic Publication     

Kinetics and mechanism of silver(I) catalyzed oxidation of tris(1,10-phenanthroline)iron(II) with peroxodiphosphate in acetate buffers

A kinetic study of the silver(I)-catalyzed oxidation of tris(1,10-phenanthroline)iron(II) with peroxodiphosphate was carried out by estimating tris-complex at 510 nm. The reaction is found to conform to the rate law (i). with K₂ and K₃ being the acid dissociation constants of H₃P₂O₈^? and H₂P₂O₈^2?, respectively. The silver(I) catalysis in the reaction has been explained on the basis of complex formation between pdp and silver(I).     

Magnetron sputtering of silver nanowires using anodic aluminum oxide template: a new active substrate of surface enhanced Raman scattering and an investigation of its enhanced mechanism

A high quality anodic aluminum oxide (AAO) template with ordered apertures about 50-80 nm was fabricated by anodizing aluminum in electrolytes through a two-step method, and silver nanowires with diameters from 40nm to 70nm were prepared on this AAO template by magnetron sputtering. On the glass covered with silver nanowires, high quality surface enhanced Raman scattering (SERS) spectra of sudan II (C₁₈H₁₆N₂O) with enhancement factors of 10⁵ were obtained. And comparison of SERS spectra on silver nanowires with the SERS spectra of silver colloids indicates that main enhanced mode is lightning rod effect of nanorods on the Sudan II/silver nanowires system.     

Quantum chemical analysis of the Eley-Rideal and Langmuir-Hinshelwood mechanisms of the catalytic oxidation of carbon monoxide on the nickel surface

The studies concerned with the oxidation of carbon monoxide on the nickel surface are reviewed. The Eley-Rideal (ER) collision and Langmuir-Hinshelwood (LH) adsorption mechanisms of the oxidation are analyzed. Calculations of the activation barriers of the oxidation of carbon monoxide on the Ni (111), (100), and (110) faces were performed for the first time and involved optimization of the reaction paths by the collision and adsorption mechanisms. It is shown that on the Ni (111) and (110) faces the ER collision mechanism of the reaction is preferable with the activation barriers ΔE _dis ^O ₂=62 kJ/mole and ΔE _trans ^O A21F5001₂x=25 kJ/mole for Ni (111) and ΔE _dis ^O ₂=72 kJ/mole and ΔE _trans ^O ₂=20 kJ/mole for Ni (110); on the Ni (100) face, the LH adsorption mechanism with the activation barriers ΔE _dis ^O ₂=75 kJ/mole and ΔE _trans ^O ₂=42 kJ/mole is favored. Analysis of the potential barriers for the catalytic oxidation of carbon monoxide on the Ni surfaces suggests the LH mechanism to be preferential, although insignificant differences in the activation barries can lead to the oscillatory reaction mechanism, which is confirmed experimentally. The calculations were performed by the LCAO MO SCF method in the MINDO/3 approximation. Kiev Polytechnical Institute. Translated fromZhurnal Struktumoi Khimii, Vol. 37, No. 4, pp. 628–645, July–August, 1996. Translated by I. Izvekova