Obtaining of Ni<Subscript>0.65</Subscript>Zn<Subscript>0.35</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposites by thermal decomposition of complex compounds embedded in silica matrix

This article presents the results of our investigation on the obtaining of Ni_0.65Zn_0.35Fe₂O₄ ferrite nanoparticles embedded in a SiO₂ matrix using a modified sol–gel synthesis method, starting from tetraethylorthosilicate (TEOS), metal (Fe^III,Ni^II,Zn^II) nitrates and ethylene glycol (EG). This method consists in the formation of carboxylate type complexes, inside the silica matrix, used as forerunners for the ferrite/silica nanocomposites. We prepared gels with different compositions, in order to obtain, through a suitable thermal treatment, the nanocomposites (Ni_0.65Zn_0.35Fe₂O₄)_x–(SiO₂)_100–x (where x=10, 20, 30, 40, 50, 60 mass%). The synthesized gels were studied by differential thermal analysis (DTA), thermogravimetry (TG) and FTIR spectroscopy. The formation of Ni–Zn ferrite in the silica matrix and the behavior in an external magnetic field were studied by X-ray diffraction (XRD) and quasi-static magnetic measurements (50 Hz).     

Preparation and characterization of multiresponsive polymer composite microspheres with core–shell structure

Fe₃O₄/SiO₂/poly (N-isopropylacrylamide-co-N,N-dimethylaminoethyl methacrylate) [P(NIPAM-co-DMA)] multiresponsive composite microspheres with core–shell structure were synthesized by template precipitation polymerization. First, the magnetite nanoparticles were coated with silica and then modified with 3-(trimethoxysilyl)-propyl methacrylate (MPS). Subsequently, the Fe₃O₄/SiO₂ particles grafted with MPS were used to seed the precipitation copolymerization of NIPAM and DMA. The composite microspheres with core–shell structure were superparamagnetic, pH-sensitive, and thermoresponsive. The swelling ratio (D_{25 °C, pH = 3}/D_{50 °C, pH = 9})³ coupling of pH and temperature increased up to 21.2, which was much higher than that without comonomer DMA.     

Electrochemical studies of LiCr x Fe x Mn2?2x O4 in an aqueous electrolyte

In this paper, LiCr _x Fe _x Mn_2−2x O₄ (x = 0, 0.05, 0.1) electrode materials were prepared by sol–gel technique and characterized by X-ray diffraction (XRD) and transmission electron microscopy or high-resolution transmission electron microscopy techniques. XRD results reveal that the Cr–Fe-co-doped LiCr _x Fe _x Mn_2−2x O₄ materials are phase-pure spinels. The electrochemical properties of the LiMn₂O₄, LiCr_0.05Fe_0.05Mn_1.9O₄, and LiCr_0.1Fe_0.1Mn_1.8O₄ electrodes in 5 M LiNO₃ aqueous electrolyte were investigated using cyclic voltammetry, AC impedance, and galvanostatic charge/discharge methods. In the current range of 0.5–2 A g⁻¹, the specific capacity of the LiCr_0.05Fe_0.05Mn_1.9O₄ electrode is close to that of the LiMn₂O₄ electrode, but the specific capacity of the LiCr_0.1Fe_0.1Mn_1.8O₄ electrode is obviously lower than that of the LiMn₂O₄ electrode. When the electrodes are charge/discharge-cycled at the high current rate of 2 A g⁻¹, the LiCr_0.05Fe_0.05Mn_1.9O₄ electrode exhibits an initial specific capacity close to that of the LiMn₂O₄ electrode, but its cycling stability is obviously prior to that of the LiMn₂O₄ electrode.     

Fe<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> Clusters (<Emphasis Type="Italic">n</Emphasis> = 2–7) Interaction with Furan Ring: DFT Studies over Iron Surface Suitability for Furan Adsorption

The interaction of different iron clusters (Fe₂, Fe₃, Fe₄, Fe₅, Fe₆ and Fe₇) with furan compound was studied by density functional theory (DFT) and the results show that the compound possess suitable structural and electronic parameters for the metal adhesion. After analyzing the binding energy and molecular orbital studies, it is found that there is a bond between furan ring and metal. In the molecular orbital, since the HOMO localizes over furan ring, especially over C2=C3–C4=C5, the furan acts as donator (HOMO) and metal performs as acceptor (LUMO) in the interaction of furan with iron surface, transferring the high charge density mainly from the delocalization region of furan ring to the metal (L(σ) → Fe).     

Electrocatalytic oxidation of pyridoxine (vitamin B<Subscript>6</Subscript>) on aluminum electrode modified by metallic palladium particles/iron (III) hexacyanoferrate (II) film

The electrocatalytic activity of a Prussian blue (PB) film on the aluminum electrode by taking advantage of the metallic palladium characteristic as an electron-transfer bridge (PB/Pd–Al) for electrooxidation of 2-methyl-3-hydroxy-4,5-bis (hydroxyl–methyl) pyridine (pyridoxine) is described. The catalytic activity of PB was explored in terms of Fe^III [Fe^III (CN)₆]/Fe^III [Fe^II (CN)₆]¹⁻ system. The best mediated oxidation of pyridoxine (PN) on the PB/Pd–Al-modified electrode was achieved in 0.5 M KNO₃ + 0.2 M potassium acetate of pH 6 at scan rate of 20 mV s⁻¹. The mechanism and kinetics of the catalytic oxidation reaction of PN were monitored by cyclic voltammetry and chronoamperometry. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The charge transfer-rate limiting reaction step is found to be a one-electron abstraction, whereas a two-electron charge transfer reaction is the overall oxidation reaction of PN by forming pyridoxal. The value of α, k, and D are 0.5, 1.2 × 10² M⁻¹ s⁻¹, and 1.4 × 10⁻⁵ cm² s⁻¹, respectively. Further examination of the modified electrodes shows that the modifying layers (PB) on the Pd–Al substrate have reproducible behavior and a high level of stability after posing it in the electrolyte or Pyridoxine solutions for a long time.     

Mixed conductivity and stability of A-site-deficient Sr(Fe,Ti)O<Subscript>3–δ</Subscript> perovskites

Deficiency in the A sublattice of perovskite-type Sr_{1– y} Fe_0.8Ti_0.2O_3–δ (y=0–0.06) leads to suppression of oxygen-vacancy ordering and to increasing oxygen ionic conductivity, unit cell volume, thermal expansion, and stability in CO₂-containing atmospheres. The total electrical conductivity, predominantly p-type electronic in air, decreases with increasing A-site deficiency at 300–700 K and is essentially independent of the cation vacancy concentration at higher temperatures. Oxygen ion transference numbers for Sr_{1– y} Fe_0.8Ti_0.2O_3–δ in air, estimated from the faradaic efficiency and oxygen permeation data, vary in the range from 0.002 to 0.015 at 1073–1223 K, increasing with temperature. The maximum ionic conductivity was observed for Sr_0.97Fe_0.8Ti_0.2O_3–δ ceramics. In the system Sr_0.97Fe_{1– x} Ti _x O_3–δ (x=0.1–0.6), thermal expansion and electron-hole conductivity both decrease with x. Moderate additions of titanium (up to 20%) in Sr_0.97(Fe,Ti)O_3–δ result in higher ionic conductivity and lower activation energy for ionic transport, owing to disordering in the oxygen sublattice; further doping decreases the ionic conduction. It was shown that time degradation of the oxygen permeability, characteristic of Sr(Fe,Ti)O_3–δ membranes and resulting from partial ordering processes, can be reduced by cycling of the oxygen pressure at the membrane permeate side. Thermal expansion coefficients of Sr_{1– y} Ti_{1– x} Fe _x O_3–δ (x=0.10–0.60, y=0–0.06) in air are in the range (11.7–16.5)×10^–6 K^–1 at 350–750 K and (16.6–31.1)×10^–6 K^–1 at 750–1050 K. Electronic Publication     

M?ssbauer spectra of iron doped CuCrS2

M?ssbauer spectroscopy is used to study the state of iron atoms in samples with a composition of CuCr_1−x Fe _x S₂ (x = 0.01–0.30). It is shown that at x ≤ 0.02 samples are solid solutions in which iron atoms have an oxidation number of 3+ and replace chromium atoms in octahedral sites. When the iron concentration increases, the second phase — chalcopyrite CuFeS₂ — forms along with the solid solution. The relative iron concentration in this phase increases from 11% at x = 0.03 to 52% at x = 0.30. Original Russian Text Copyright ? 2009 by V. A. Varnek, V. V. Sokolov, I. Yu. Filatova, and S. A. Petrov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 2, pp. 365–368, March–April, 2009.     

Synthesis and Properties of The Solid Solutions Formed in The Fe2V4O13–Cr2V4O13 System

DTA and XRD studies of the Fe₂V₄O₁₃–Cr₂V₄ O₁₃ system have shown that continuous solid solutions of a Fe_2–xCr_xV₄O₁₃ type, bearing a Fe₂ V₄ O₁₃ structure, are formed in the system. With the increasing degree of the Cr3+ ion incorporation into the Fe₂ V₄ O₁₃ structure, a contraction of the solid solution crystal lattice develops. Solid solutions of a Fe_2–x Cr_x V₄ O₁₃ type melt incongruently, their melting temperature increasing from 953 to 1003 K with increase in the degree of the Cr³⁺ ion incorporation. The solid product of melting Fe_2–x Cr_x V₄ O₁₃ solid solutions for 0.2<x >1.2 is the Fe_1–x Cr_x VO₄ solution phase, and for x ≤0.2 and x ≥1.4 – the Fe_1–x Cr_x VO₄ phase as well as FeVO₄ or CrVO₄ , respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Application of the “Tg-Δ rule” to the local structural study of ferrate glasses

A linear relationship exists between the glass transition temperature (T _g) and the quadrupole splitting (Δ) of Fe(III). The linear relationship, termed ‘T _g-Δ rule’, has been verified in 60CaO·(40-x)Al₂O₃·xFe₂O₃, 60CaO·10BaO·(30-x) Al₂O₃·xFe₂O₃, 60CaO·(40-x)Ga₂O₃·xFe₂O₃, and 50CaO·(50-x)Ga₂O₃·xFe₂O₃ glasses. In these glasses, both theT _g and Δ decrease linearly with an increasing content of Fe₂O₃ (≈40 mol%). The slope of the straight line, obtained from the plot of theT _g vs. Δ, was calculated to be 670≈700, °C/(mm·s⁻¹), revealing that the Fe(III) constitutes the skeleton of aluminoferrate and galloferrate glasses.     

Synthesis and Structural Characterization of a New Macrocyclic Polysiloxane-immobilized Ligand System

Summary. A new porous solid macrocyclic 1,4,7,11,14-pentaazapentadecane-3,15-dione polysiloxane ligand system of the general formula P–(CH₂)₃–C₁₁H₂₂O₂N₅ (where P represents [Si–O]_n siloxane network) has been prepared by the reaction of polysiloxane-immobilized iminobis(N-(2-aminoethyl)acetamide) with 1,3-dibromopropane. The FTIR and XPS results confirm the introduction of the macrocyclic functional ligand group into the polysiloxane network. The new macrocyclic polysiloxane ligand system exhibits high potential for the uptake of metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺).     

Vacancy Contents in MnZn Ferrites From TG Curves

Expressions for calculating the cation vacancy contents of MnZn ferrites from thermogravimetric curves are presented together with some experimental data. In a single-phase MnZn ferrite synthesized by conventional ceramic procedures, the O₂ evolution accompanying ferrite formation follows the formal equation. Mn²⁺ _σα Zn_σβ Fe³⁺ _2σ(1–γ) [V ]_{σ/4(1–2γ)} O₄ =σ'/σ Mn²⁺ _σ(α–2ϕ) Zn_σβ Fe²⁺ _2σθ Mn³⁺ _2σϕ Fe³⁺ _{2σ(1–γ–θ)} [V ]_{σ/4(1–2γ–3ϕ)} O₄ +σ'φ/2O₂ (g) where α and β denote the MnO and ZnO mole fractions in the primary mixture γ=α+β, θ and ϕ depend on the quantities of Fe²⁺ and Mn³⁺ formed, respectively, φ=θ–ϕ and σ'/σ is a function of the former parameters. Even though the relative amounts of Fe²⁺ /Fe³⁺ and Mn²⁺ /Mn³⁺ remain uncertain, the vacancy content [V ] of the ferrite can be determined because it depends on φ alone, which is related to the change in mass of the sample as the synthesis takes place through the equation φ=(1.5–γ) μ_β /μ_O2 (1–m _f /m _i ) Here, m _i and m _f are the masses of the sample before and after O₂ evolution, μ_B is the formula mass of the ferrite and μ_O2 is the O₂ molar mass. Practically vacancy-free single-phase MnZn ferrite samples were obtained by sintering in air at 1250°C and cooling in pure N₂ . This revised version was published online in July 2006 with corrections to the Cover Date.     

1A1 5T2 Spin transition in the solid phases of FexNi1-x(ATr)3(NO3)2 (ATr = 4- amino- 1,2,4- triazole)

The effect of Fe²⁺ substitution by Ni²⁺ in the complex of iron(II) nitrate with 4- amino- 1,2,4- triazole Fe(ATr)₃(NO₃)₂ on the character of the¹A₁ ⁵T₂ spin transition (ST) is studied by magnetic susceptibility and calorimetry methods. Solid phases of Fe_xNi_{1- x}(ATr)₃(NO₃)₂ (0.1 ≤ x ≤ 0.9) were synthesized. The temperature dependences of the effective magnetic moment were measured in the range of 78– 360 K. Heat capacities were measured in the range of 210– 340 K for 0.1 ≤ x ≤ 0.5 and in the range of 230– 340 K for 0.6 ≤x ≤ 0.9. As x decreases, the transition temperature (T_C), hysteresis (δT_C, and transition enthalpy (δH) decrease and the ST is leveled. The results are compared with the data obtained previously for the solid phases of Fe_xZn_{1- x}(ATr)₃(NO₃)₂ (0.01 ≤ x ≤ 0.8). The dependence Μ_eff(T) is analyzed theoretically in terms of both the domain model and the spin equilibrium model. Translated fromZhumal Strukturnoi Khimii, Vol. 38, No. 4, pp. 696–703, July–August, 1997.     

Synthesis and Structural Characterization of a New Macrocyclic Polysiloxane-immobilized Ligand System

A new porous solid macrocyclic 1,4,7,11,14-pentaazapentadecane-3,15-dione polysiloxane ligand system of the general formula P–(CH₂)₃–C₁₁H₂₂O₂N₅ (where P represents [Si–O]_n siloxane network) has been prepared by the reaction of polysiloxane-immobilized iminobis(N-(2-aminoethyl)acetamide) with 1,3-dibromopropane. The FTIR and XPS results confirm the introduction of the macrocyclic functional ligand group into the polysiloxane network. The new macrocyclic polysiloxane ligand system exhibits high potential for the uptake of metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺).     

Formation of the silylene-bridged complex Fe2(CO)6(μ2-SiCl2)3 from cis-Fe(CO)4(SiCl3)2: an experimental and computational study

Abstract  

Thermolysis of cis-Fe(CO)₄(SiCl₃)₂ results in the formation of the novel compound Fe₂(CO)₆(μ₂-SiCl₂)₃, which was characterized by single crystal X-ray diffraction. Density functional theory calculations were carried out to elucidate possible reaction steps leading to the formation of Fe₂(CO)₆(SiCl₂)₃, including CO dissociation and chlorine abstraction by a SiCl₃ radical generated from homolytic Fe–Si bond cleavage involving a singlet–triplet intersystem crossing.     

A novel 18-membered metallacrown containing a double-azathiacrown

A new type of 18-metallacrown-6, [Fe₆(H₂O)₆L₆] (L = 1-(2-hydroxy-benzoyl)-thiosemicarbazide), has been prepared and characterized. The backbone of this metal-organic assembly is the double-azathiacrown, which is formed by six repeating units of the five-membered rings [Fe–S–C–N–N]. It is the first metal complex containing a double-azathiacrown. Due to the meridional coordination of the ligand to the Fe³⁺ ion, the ligand enforces the stereochemistry of the Fe³⁺ ions as a propeller configuration with alternating Λ/Δ forms. Antibacterial screening data showed that the metallacrown has strong antimicrobial activity against Escherichia coli and Staphylococcus aureus.     

Synthesis and reactivity of metal-containing monomers

Thermal transformations of Fe^III maleate, [Fe₃O(OOCCH=CHCOOH)₆]OH·3H₂O (1), in an autogenerated atmosphere and the change in the short-range surrounding of Fe atoms during thermolysis were studied. The thermal transformations of1 are accompanied by the following processes: dehydration with simultaneous rearrangement of the ligand environment and formation of maleic acid, and polymerization of the rearranged monomer and its decarboxylation at high temperatures. In the initial stage of decarboxylation, the destruction of the metal-carboxylate Fe₃O complex occurs followed by the formation of the Fe−Fe bond (r=0.246 nm). The oxidation of the Fe atoms is observed when the thermolysis duration increases. For Part 49, seeIzv. Akad. Nauk, Ser. Khim., 1998; 1145 [Russ. Chem. Bull., 1998,47, 1113 (Engl. Transl.)]. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1505–1510, August, 1998.     

Synthesis and Properties of Solid Solutions in The FeVMoO7–CrVMoO7 System

X-ray phase analysis (XRD), differential thermal analysis (DTA) and IR spectroscopy have shown that continuous substitution solid solutionsin are formed in the FeVMoO₇–CrVMoO₇ system. With increasing the degree of Cr³⁺ ion incorporation into the FeVMoO₇ structure, a crystal lattice contraction of the Fe_1–xCrxVMoO₇ solid solution arise. Elevation of temperature of its incongruent melting and gradual shifting of the corresponding IR absorption bands towards higher wavenumbers have been noticed, as well. The solid product of incongruent melting for x≤0.5 is the Fe_4–yCr_yV₂ Mo₃ O₂₀ solid solutions phase, whereas for x>0.5 Fe_2–zCr_z(MoO₄)₃ and Fe_2–u Cr_u O₃ solid solutions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Probing the structural effects on the intrinsic electronic and redox properties of [2Fe–2S]<Superscript>+</Superscript> clusters,a broken-symmetry density functional theory study

In biological electron transport chains, [2Fe–2S] clusters have versatile electrochemical properties and serve as important electron carriers in a wide variety of biological processes. To understand structural effects on the variation in reduction potentials in [2Fe–2S] proteins, a series of [2Fe–2S] protein analogs with bidentate ligands ( − SC ₂ H ₄ NH ₂) were recently produced by collision-induced dissociation of [Fe ₄ S ₄(L)₄]²⁻ (L = SC ₂ H ₄ NH ₂). Combined with photoelectron spectroscopy findings, the reaction mechanisms of [Fe ₄ S ₄(L)₄]²⁻ to [Fe ₂ S ₂(L)₂]⁻ and the structural effects of ligands on the electronic and redox properties of the [2Fe–2S] clusters are investigated here using broken-symmetry density functional theory method. Our calculations suggest that [Fe ₂ S ₂(η² − L)(cis − L)]⁻ and [Fe ₂ S ₂(η² − L)₂]⁻ are the experimentally observed [2Fe–2S] products, which are generated via a fission process of [Fe ₄ S ₄(L)₄]²⁻ followed by rearrangement of ligands of [Fe ₂ S ₂(L)₂]⁻. Moreover, structural variation of the ferrous center may dramatically affect the oxidation energy of the [2Fe–2S] clusters.     

Phosphodiester hydrolysis promoted by dinuclear iron(III) complexes

We report the reactivity of three binuclear non-heme Fe(III) compounds, namely [Fe₂(bbppnol)(μ-AcO)(H₂O)₂](ClO₄)₂ (1), [Fe₂(bbppnol)(μ-AcO)₂](PF₆) (2), and [Fe₂(bbppnol)(μ-OH)(Cl)₂]·6H₂O (3), where H₃bbppnol = N,N′-bis(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)–1,3-propanediamine-2-ol, toward the hydrolysis of bis-(2,4-dinitrophenyl)phosphate as models for phosphoesterase activity. The synthesis and characterization of the new complexes 1 and 3 was also described. The reactivity differences observed for these complexes show that the accessibility of the substrate to the reaction site is one of the key steps that determinate the hydrolysis efficiency.     

Thermal decomposition of dinuclear complexes LM(μ-OOCR)<Subscript>4</Subscript>ML (L is α-substituted pyridine)

The solid-state thermal decomposition of the tetrabridged dinuclear Mn^II, Fe^II, Co^II, Ni^II, and Cu^II pivalate complexes with apical α-substituted pyridine ligands containing different substituents (2,3-dimethylpyridine or quinoline) was studied by differential scanning calorimetry and thermogravimetry. The decomposition of the Co^II complexes is accompanied by the aggregation to form the volatile octanuclear complex Co₈(μ₄-O)₂(μ_n-OOCCMe₃)₁₂, where n = 2 or 3, whereas the thermolysis of the Mn^II, Fe^II, Ni^II, and Cu^II complexes is accompanied by the degradation of the starting compounds, the phase composition of the decomposition products being substantially dependent on the nature of metal and the apical organic ligand. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1650–1659, September, 2007.