Synthesis of crystallized mesoporous transition metal oxides by silicone treatment of the oxide precursor

Ordered mesoporous transition metal oxides were successfully crystallized after strengthening the amorphous framework by a silica layer, which efficiently protected the original mesoporous structure against crystallization and resulting mass transfer.     

Synthesis,characterization and properties of polyaniline doped with transition metal substituted silicotungstate

Polyaniline hybrid material doped with transition metal mono-substituted silicotungstate β₂-K₆[SiW₁₁M(H₂O)O₃₉]?·?xH₂O (M?=?Mn²⁺, Co²⁺, Cu²⁺, Fe²⁺) were prepared for the first time. Their scanning electron microscopy (SEM), infrared (IR), UV–Vis, and X-ray diffraction (XRD) patterns confirm the existence of Keggin anions and form the space reticular structure. The material exhibits excellent proton conduction, its proton conductivity is 9?×?10^?2?s?cm^?1 at room temperature (20°C).     

17O and 15N solid state NMR studies on ligand-assisted templating and oxygen coordination in the walls of mesoporous Nb, Ta and Ti oxides

A multinuclear solid state NMR approach is applied to four templated mesoporous oxides (silica, titania, niobia and tantala) to include (15)N and (17)O magic angle spinning (MAS) NMR and double resonance (15)N-(93)Nb, (17)O Rotational-Echo Adiabatic Passage Double Resonance (REAPDOR). The templated samples were ramped in steps of 20 degrees C for 2 days up to typically 110 degrees C where the samples were left for 2-4 days. (15)N MAS NMR shows that amines are the only species present in the TiO2, Nb2O5, and Ta2O5. In SiO2, amines are only present as a minor coordination (10 +/- 2%), but there are several strong ammonium (15)N resonances. The REAPDOR experiments show that the nitrogen interacts with niobium, confirming a ligand interaction between the Nb and N, as previously believed. In the case of silica, the amine is quaternized and there is apparently no interaction with the Si, suggesting a RNH3(+) (-)O-Si- hydrogen-bonding interaction with the walls. (17)O MAS NMR provides the clearest indication of the local wall structure. In the aged, templated samples in all cases only OM2 coordinations are present which is very different from the pure bulk oxides (apart from SiO2) and must be due to the effects of amine coordination at the metal centers. On removal of the template, these oxides behave differently, with Ta2O5 showing a mixture of OTa2 (85 +/- 5%) and OTa3 (15 +/- 5%) which is similar to the types of coordination found in the bulk oxide. The previously reported (17)O MAS NMR data from heat-treated mesoporous niobia shows only ONb2, which is very highly ordered. In contrast for titania, the OTi2 coordination is immediately lost on removal of the template to be replaced by a mixture of OTi3 (60 +/- 5%) and OTi4 (40 +/- 5%), with the OTi4 becoming dominant above 250 degrees C, very different behavior from the corresponding bulk oxide. In summary, this NMR study shows that the local oxygen coordination in amine-templated mesoporous transition metal oxides is present as OM2 which is relatively rare in bulk oxides. The data indicates that the template interaction is largely controlled by the N-M dative bond to the wall, suppressing higher oxygen coordination numbers. Qualitatively it appears that the strength of this interaction varies greatly in the different mesoporous oxides.     

Synthesis,characterization and redox properties of a new vic-dioxime and its transition metal complexes

A novel vic-dioxime, 1,2 dihydroxyimino-1-p-tolyl-3-aza-6-morpholine heptane (LH₂) was prepared by reacting anti-p-tolylchloroglyoxime with 4-(3-aminopropyl)morpholine in absolute THF. Mononuclear complexes with a metal–ligand ratio of 1:2 were prepared using Co^II, Cu^II and Ni^II salts. The ligand and its complexes were characterized by elemental analyses, FT-IR, u.v.–vis., ¹H- and ¹³C-n.m.r. spectra, magnetic susceptibility measurements, thermogravimetric analyses (t.g.a.), and by cyclic voltammetry.     

Synthesis,characterization and antimicrobial activity of a new macrocycle and its transition metal complexes

The semicarbazone (L¹) has been prepared by reaction of semicarbazide and glutaraldehyde (2 : 1) in distilled water and methanol (1 : 1). The reaction of semicarbazide, glutaraldehyde and diethyl oxalate in distilled water and methanol gave Schiff-base L², 1,2,4,7,9,10-hexaazacyclo-pentadeca-10,15-dien-3,5,6,8-tetraone. Complexes of first row transition metal ions Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) have also been synthesized. The ligand and its complexes were characterized by elemental analysis, molar conductance, magnetic moment measurements, IR, ¹H NMR, UV–Visible spectra and thermogravimetric analysis (TGA). Molar conductance values show that the complexes of Ni(II), Cu(II), Zn(II), Mn(II) and Co(II) are 1 : 2 electrolytes. On the basis of electronic spectral studies and molar conductance measurements an octahedral structure has been proposed for Mn(II) and Co(II) complexes, tetrahedral for Zn(II) complex and square planar for Ni(II) and Cu(II). The thermal behavior of the compounds, studied by TGA in a nitrogen atmosphere up to 800°C, reveal that the complexes have higher thermal stability than the macrocycle. All the synthesized compounds and standard drugs kanamycin (antibacterial) and miconazole (antifungal) have been screened against bacterial strains Staphylococcus areus, Escherichia coli and fungal strains Candida albicans, Aspergillus niger. The metal complexes inhibit growth of bacteria to a greater extent than the ligand.     

Structural characterization of tellurite glasses doped with transition metal oxides using Raman spectra and ab initio calculations

Systems of iron tellurite glasses were prepared by melt quenching with compositions of [85%TeO2+5%Fe2O3+10%TMO], where transition metal oxides (TMO) are TiO2, V2O5, MnO, CoO, NiO and CuO. Furthermore, the main structural units of these samples have been characterized by means of Raman spectra (150-1200 cm(-1)) as well as wavenumber predictions by means of Gaussian 98 ab initio calculations for the proposed site symmetries of TeO4(4-) triagonal bipyramid (C2v) and Te2O7(6-) bridged tetrahedra (Cs and C1). Aided by normal coordinate analysis, calculated vibrational frequencies, Raman scattering activities, force constants in internal coordinates and potential energy distributions (PEDs), revised vibrational assignments for the fundamental modes have been proposed. The main structural features are correlated to the dominant units of triagonal bipyramid (tbp) or bridged tetrahedral (TeO3+1 binds to TeO3 through TeOTe bridge; corner sharing). Moreover, the Raman spectra of the investigated tellurites reflect a structural change from tbp (coordination number is four) to triagonal pyramidal (coordination number is three).     

Synthesis and characterization of new quaternary polyselenide Ba4TMSbSe12 (TM = Nb,Ta)

Two new quaternary polyselenides, Ba₄TMSbSe₁₂ (TM = Nb, Ta), are synthesized using a solid state reaction. They crystallize in a new structural type with a P‐1 triclinic space group, characterized according to single‐crystal X‐ray diffraction. The structure is alternately stacked using isolated NbSe₉^5? and SbSe₃^3?, which are separated by Ba²⁺. The structure contains the NbSe₉^5? unit with a bipentagonal pyramidal shape coordinated with Se^2? and Se₂^2? in monodenteate and bidentate modes. The vibrational property of the diselenide Se₂^2? unit was studied using Raman spectrum analysis. ultraviolet–visible diffused reflectance and temperature‐dependent resistivity measurements indicate semiconductor behaviors. Calculations of electronic structures indicate the presence of a band gap and strong Se‐Se interactions in the diselenide group, which experimentally supports the measured physical properties.     

Synthesis and characterization of mesoporous nickel oxide for electrochemical capacitor

A mesoporous electrochemical active material NiO with face center cubic structure has been synthesized using supramolecular as template and urea as hydrolysis-controlling agent. The synthesized product was characterized physically by thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, and Brunauer–Emmett–Teller-specific surface area measurement. Electrochemical characterization was performed using cyclic voltammetry and chronopotentiometry in 6 mol/l KOH aqueous solution electrolyte. A specific capacitance of approximately 327 F/g was obtained by annealing the sample at 350 °C. To get a better understanding of the effect of supramolecular template on improving the structure property and electrochemical performance, a compared experiment was also carried out in this work.     

Synthesis and characterization of Zr-SBA-15 supported tungsten oxide as a new mesoporous solid acid

A series of materials WO₃/Zr-SBA-15 were synthesized by modifying zirconium-incorporated SBA-15 mesoporous molecular sieve with various loadings of tungsten oxide, followed by calcining at different temperatures. The structures and the surface states of these materials were determined by XRD, TEM, N₂ adsorption–desorption and Raman spectroscopy, while the surface acidities were characterized by FT-IR spectroscopy of pyridine adsorption, NH₃-TPD, and the Hammett indicator method. To evaluate the catalytic activities of the prepared materials, the benzoylation of anisole was chosen as the model reaction. All the results reveal that the synthesized samples are strong solid acids, even solid superacids under some conditions, with uniform mesoporous structure and high surface area. The dispersion state of the supported WO₃, which depends on the WO₃ loading and the calcination temperature, has a direct influence on the acidity and catalytic activity of the materials. Moreover, the high acid strength is attributed to the WO bond nature of the complex formed by the interaction between WO₃ and the surface of Zr-SBA-15.     

Synthesis, characterization and thermal analysis of some new transition metal complexes of a polydentate Schiff base

A new polydentate Schiff base (H3L) was synthesized from the condensation of 2,6-diformyl-4-methylphenol and S-methylhydrazine-carbodithionate. The 1:1 metal complexes were obtained from the interaction of H3L and the metal ions Cr(III), Co(II), Ni(II), Cu(II), Cd(II) and Hg(II). The complexes were characterized by elemental analysis and IR spectroscopy. Detailed studies of the thermal properties of the complexes were investigated by thermogravimetry techniques.     

Synthesis, characterization and formation process of transition metal oxide nanotubes using carbon nanofibers as templates

Mono and binary transition metal oxide nanotubes could be synthesized by the immersion of carbon nanofiber templates into metal nitrate solutions and removal of the templates by heat treatment in air. The transition metal oxide nanotubes were composed of nano-crystallites of metal oxides. The functional groups on the carbon nanofiber templates were essential for the coating of these templates: they acted as adsorption sites for the metal nitrates, ensuring a uniform metal oxide coating. During the removal of the carbon nanofiber templates by calcination in air, the metal oxide coatings promoted the combustion reaction between the carbon nanofibers and oxygen.     

Nonaqueous synthesis of metal oxide nanoparticles: Short review and doped titanium dioxide as case study for the preparation of transition metal-doped oxide nanoparticles

The liquid-phase synthesis of metal oxide nanoparticles in organic solvents under exclusion of water is nowadays a well-established alternative to aqueous sol–gel chemistry. In this article, we highlight some of the advantages of these routes based on selected examples. The first part reviews some recent developments in the synthesis of ternary metal oxide nanoparticles by surfactant-free nonaqueous sol–gel routes, followed by the discussion of the morphology-controlled synthesis of lanthanum hydroxide nanoparticles, and the presentation of structural peculiarities of manganese oxide nanoparticles with an ordered Mn vacancy superstructure. These examples show that nonaqueous systems, on the one hand, allow the preparation of compositionally complex oxides, and, on the other hand, make use of the organic components (initially present or formed in situ) in the reaction mixture to tailor the morphology. Furthermore, obviously even the crystal structure can differ from the corresponding bulk material like in the case of MnO nanoparticles. In the second part of the paper we present original results regarding the synthesis of dilute magnetic semiconductor TiO₂ nanoparticles doped with cobalt and iron. The structural characterization as well as the magnetic properties with special attention to the doping efficiency is discussed.     

Synthesis and characterization of mesoporous indium tin oxide possessing an electronically conductive framework

The new mesoporous transparent conducting oxide based on indium-tin-oxide, meso-ITO, has been synthesized by a modified sol-gel method, using CTAB as the surfactant. Critical was the employment of triethanolamine to control the rate of hydrolysis and inhibit deposition of the bulk oxides. Removal of the surfactant by calcination yielded a relatively well-ordered worm-hole motif arrangement of pores visible in the TEM and stable to 400 degrees C. BET measurements revealed no hysteresis in the absorption-desorption isotherm, consistent with a narrow pore-size distribution (between 20 and 40 A depending on the In:Sn ratio); surface areas ranged between 270 and 310 m2/g. This colorless material is the first mesoporous oxide exhibiting substantial framework conductivity, with a conductivity at 25 degrees C of 1.2 x 10-3 S/cm. This distinguishes it from mesoporous mixed-valence transition-metal oxides that exhibit weak hopping semiconductor behavior and much lower conductivity.     

Synthesis and characterization of monodisperse, mesoporous, and magnetic sub-micron particles doped with a near-infrared fluorescent dye

Recently, multifunctional silica nanoparticles have been investigated extensively for their potential use in biomedical applications. We have prepared sub-micron monodisperse and stable multifunctional mesoporous silica particles with a high level of magnetization and fluorescence in the near infrared region using an one-pot synthesis technique. Commercial magnetite nanocrystals and a conjugated-NIR-dye were incorporated inside the particles during the silica condensation reaction. The particles were then coated with polyethyleneglycol to stop aggregation. X-ray diffraction, N₂ adsorption analysis, TEM, fluorescence and absorbance measurements were used to structurally characterize the particles. These mesoporous silica spheres have a large surface area (1978 m²/g) with 3.40 nm pore diameter and a high fluorescence in the near infrared region at λ=700 nm. To explore the potential of these particles for drug delivery applications, the pore accessibility to hydrophobic drugs was simulated by successfully trapping a hydrophobic ruthenium dye complex inside the particle with an estimated concentration of 3 wt%. Fluorescence imaging confirmed the presence of both NIR dye and the post-grafted ruthenium dye complex inside the particles. These particles moved at approximately 150 μm/s under the influence of a magnetic field, hence demonstrating the multifunctionality and potential for biomedical applications in targeting and imaging.     

Functionalized SBA-15 mesoporous silica in ion chromatography of alkali,alkaline earths,ammonium and transition metal ions

The retention properties of a SBA-15 mesoporous silica functionalized with –(CH₂)₃COOH groups, synthesized by a co-condensation route, were investigated for the ion chromatography of different cationic species. A systematic study on the effect of different eluent compositions containing non-complexing (methanesulfonic acid) or complexing (oxalic or pyridine-2,6-dicarboxylic acids) eluents, in the presence of organic modifiers (CH₃CN, CH₃OH, CH₃NH₂) on the retention of cations (Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Sr²⁺, Ba²⁺, NH₄⁺, Cu²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Co²⁺, Pb²⁺, Fe³⁺) chosen as model analytes and for their environmental importance, allowed us to elucidate the mechanisms (cation-exchange or complexation) involved in the retention on the SBA-15 phase. For the first time separations of cations on SBA-15 based stationary phases are investigated, providing the basis for further development of mesoporous silica chemistry for in-flow ion-exchange applications.     

Hydrolysis reactions of transition metal fluorides in liquid hydrogen fluoride: Oxonium salts with Nb,Ta and W

The hydrolysis reactions of the hexafluorides of molybdenum and tungsten, the pentafluorides of niobium and tantalum and the tetrafluorides of zirconium and hafnium have been studied in liquid hydrogen fluoride. The following new compounds have been isolated and characterized: H₃O⁺WOF^-₅, H₃O⁺NbF^-₆ and H₃O⁺TaF^-₆. Hydrolysis of MoF₆ leads to MoOF₄, but in HF solution there is evidence for the existence of MoOF^-₅ ion.     

Synthesis and characterization of undecatungstotitanates incorporating a lanthanide or a transition metal

Summary K_n[TiW₁₁M(H₂O)O₃₉]·xH₂)(M=F, Co, Cr, Cu, Mn or Zn) and K₁₃[Ln(TiW₁₁O₃₉)₂]·xH₂O (Ln=a lanthanide) complexes have been prepared and characterized by elemental analysis, by u.v.-vis. and i.r. spectroscopy, by magnetic susceptibility measurements and by thermal measurements.     

Synthesis,structure, and photocatalytic properties of titanium(IV) oxide modified with silver oxide nanoparticles on a boron-containing mesoporous support

A method for the synthesis of TiO₂–B₂O₃–Ag composite has been proposed. The composite structure and phase composition have been determined by X-ray diffraction analysis, IR spectroscopy, and scanning as well as transmission electron microscopy. The introduction of boron oxide in the TiO₂–Ag composite enhances catalytic activity of the samples in the reactions of methyl orange photodecomposition.     

Synthesis and structure of Ta4S9Br8. An emergent family of early transition metal chalcogenide clusters

Single crystals of Ta4S9Br8 are obtained by heating Ta, S, and Br2 at 400 degrees C in a 4.0:9.0:4.0 molar ratio in a 44% yield. The structure was determined by X-ray analysis and consists of molecular clusters [Ta4(mu4-S)(mu-S2)4Br8]. The tantalum atoms form a square with long Ta...Ta distances (3.30 angstroms), with four S2 ligands bridging the Ta-Ta edges and one capping the square. Each Ta atom has two terminal bromine atoms. The compound is diamagnetic and has only two electrons for metal-metal bonding. IR and Raman spectral studies with the use of 34S allow to identify characteristic vibrations S-S (537 cm(-1)) and Ta4-mu4-S (407 cm(-1)). The compound is soluble in CH3CN, giving a dark-red solution with a characteristic electronic spectrum, which was assigned on the base of DFT calculations. ESI-MS spectra of the solutions show formation of [[Ta4S9Br8]Br]- associates.     

Synthesis and characterization of volatile, thermally stable, reactive transition metal amidinates

A series of homoleptic metal amidinates of the general type [M(R-R'AMD)(n)](x) (R = (i)Pr, (t)Bu, R' = Me, (t)Bu) has been prepared and structurally characterized for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. In oxidation state 3, monomeric structures were found for the metals Ti(III), V(III), and La(III). Bridging structures were observed for the metals in oxidation state 1. Cu(I) and Ag(I) are held in bridged dimers, and Ag(I) also formed a trimer that cocrystallized with the dimer. Metals in oxidation state 2 occurred in either monomeric or dimeric form. Metals with smaller ionic radii (Co, Ni) were monomeric. Larger metals (Fe, Mn) gave monomeric structures only with the bulkier tert-butyl-substituted amidinates, while the less bulky isopropyl-substituted amidinates formed dimers. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. They have high volatility, high thermal stability, and high and properly self-limited reactivity with molecular hydrogen, depositing pure metals, or water vapor, depositing metal oxides.