Synthesis,structure, and substitution reactivity of a new bi-oxo capped molybdenum cluster: [Mo3(μ3-O)2(μ-O2CCH2Cl)6(H2O)2(OH)]+

A new bi-oxo capped molybdenum carboxylate, [Mo₃(μ₃-O)₂(μ-O₂CCH₂Cl)₆(H₂O)₂(OH)]⁺, was synthesized by refluxing [Mo₃(μ₃-O)₂(μ-O₂CCH₃)₆(H₂O)₃]^2 + in chloroacetic acid for 20 h (T = 110 °C). Using ion-exchange chromatography (0.5 M NaClO₄ eluant), the trinuclear molybdenum ion was isolated and allowed to crystallize slowly (T = 4 °C) as the perchlorate salt (yield 23%). Upon dissolution of the compound in methanol-d₄, substitution of the terminal ligands for solvent occurs readily in which the observed exchange rate constant is k_obs^298K = 5.3 × 10^− 5 (± 0.3) s^− 1 and activation parameters equal to ΔH³ = 130 (± 10) kJ mol^− 1 and ΔS³ = 111 (± 33) J mol^− 1 K^− 1. From the kinetic data, we find that ligand substitution follows a dissociative pathway and that rates of substitution are faster than expected when compared to the molybdenum acetate analog. Herein, we report the synthesis, crystallographic study, and substitution reactivity of a new molybdenum bi-oxo capped cluster with bridging chloroacetate ligands.     

Aqueous chemical solution deposition of ultra high-k LuFeO3 thin films

Thin orthorhombic ultra high-k LuFeO₃ (LFO) films on Si₃N₄/SiO₂/Si substrates were obtained by means of aqueous chemical solution deposition (CSD). Prior to thin film deposition, the precursor synthesis, thermal decomposition and crystallization behavior of the bulk material were studied. It was shown that phase-pure hexagonal LFO powder could be formed at 650 °C while a higher temperature of 900 °C was required to obtain the orthorhombic phase. Deposition on SiO₂/Si resulted in the development of silicates in this temperature range, thus preventing the formation of the orthorhombic LuFeO₃ phase. The use of Si₃N₄/SiO₂/Si as the substrate shifted the silicate formation to higher temperature, allowing the synthesis of phase-pure orthorhombic LuFeO₃ as a thin film at 1000 °C. Impedance spectroscopy analyses confirmed its associated ultra high dielectric constant (>10,000) at room temperature for frequencies lower than or equal to 1 kHz.     

Experimental study on the stability of graphitic C3N4 under high pressure and high temperature

The stability and decomposition of graphitic C₃N₄ (g-C₃N₄) were studied in the pressure and temperature range of 10–25 GPa and up to 2000 °C by multi-anvil experiments and phase characterization of the quenched products. g-C₃N₄ was found to remain stable at relatively mild temperatures, but decomposes to graphite and nitrogen at temperatures above 600–700 °C and up to 15 GPa, while it decomposes directly to diamond (plus nitrogen) above 800–900 °C and between 22 and 25 GPa. The estimated decomposition curve for g-C₃N₄ has a positive slope (~ 0.05 GPa/K) up to ~ 22 GPa, but becomes inverted (negative) above this pressure. The diamond formed through decomposition is characterized by euhedral crystals which are not sintered to each other, but loosely aggregated, suggesting the crystallization in a liquid (nitrogen) medium. The nitrogen release from the graphitic CN framework may also play an important role in lowering the activation energy required for diamond formation and enhancing the grain growth rate. No phase transition of g-C₃N₄ was found in the studied P–T range.     

Synthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4

The nanocomposites of WO₃ nanoparticles and exfoliated graphitized C₃N₄ (g-C₃N₄) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions.The WO₃ nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C₃N₄ particles were prepared by calcination of melamine forming bulk g-C₃N₄, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m² g⁻¹.The nanocomposites were prepared by mixing of WO₃ nanoparticles and g-C₃N₄ structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 °C. The real content of WO₃ was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C₃N₄ particles were covered by the WO₃ nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO₃ nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively.The formation of heterojunction between both components was investigated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO₃, which was explained by shielding of the g-C₃N₄ surface by bigger WO₃ agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.     

Catalytic properties in N2O decomposition of mixed cobalt–iron spinels

The effect of introduction of iron in the Co_3 − xFe_xO₄ on catalytic activity in N₂O decomposition was investigated. The spinel catalysts were characterized by XRD, SEM, RS, BET methods, work function measurements and Mössbauer spectroscopy. Introduction of iron in the Co_3 − xFe_xO₄ spinel catalysts at the level of x < 1 leads to preferential substitution of Fe³⁺ in tetrahedral sites, whereas for x > 1 also octahedral ones are substituted. A strong correlation between deN₂O activity (T_50%) and work function was observed showing that electronic factor controls the catalytic reactivity of Co–Fe spinels. The results revealed that the active centers for N₂O decomposition are cobalt ions and thus even a low level of their substitution by iron leads to substantial decrease of the deN₂O activity of the cobalt spinel.     

Improved photovoltaic performances of Ru (II) complex sensitized DSSCs by co-sensitization of carbazole based chromophores

Herein, we report photovoltaic performance studies of three carbazole based dyes (N_1–3) derived from (Z)-3-(9-hexyl-9H-carbazol-3-yl)-2-(thiophen-2-yl)acrylonitrile scaffold as effective co-sensitizers in Ru (II) complex, i.e. NCSU-10 sensitized DSSCs. From the results it is evident that, the device fabricated using co-sensitizer N₃ with 0.2 mM of NCSU-10 exhibited improved photon conversion efficiency (PCE) of 8.73% with J_SC of 19.87 mA·cm^− 2, V_OC of 0.655 V and FF of 67.0%, while N₁ displayed PCE of 8.29% with J_SC of 19.75 mA·cm^− 2, V_OC of 0.671 V and FF of 62.6%, whereas NCSU-10 (0.2 mM) alone displayed PCE of 8.25% with J_SC of 20.41 mA·cm^− 2, V_OC of 0.667 V and FF of 60.6%. However, their EIS studies confirm that, N₁, showing higher V_OC is efficient in suppressing the undesired charge recombination in DSSCs through enhanced surface coverage on TiO₂ and thereby resulting in longer electron lifetime than that of NCSU-10 dye alone. Here, the higher PCE of N₃ can be attributed to its improved light harvesting efficiency, which is due to the presence of highly electron withdrawing barbituric acid in its structure. Conclusively, the results showcase the potential of simple carbazole based dyes as co-sensitizers in improving efficiency of DSSCs.     

Solvent directed assembly of two zinc(II)-2-(4-pyridyl)-4,5-imidazoledicarboxylate frameworks

Two zinc(II)-2-(4-pyridyl)-4,5-imidazoledicarboxylate frameworks, formulated as {[Zn₃(HPIDC)₃(DMF)₂](DMF)₂(H₂O)₂}_n (1) and {[Zn₄(HPIDC)₄(DMF)₄](DMF)₂(FMA)₂(H₂O)}_n (2) (H₃PIDC = 2-(4-pyridyl)-1H-4,5-imidazoledicarboxylic acid, DMF = N,N′-dimethylformamide, FMA = formamide) have been solvothermally synthesized depending on whatever solvents are used. In both structures, the HPIDC^2 − anions act as tripodal connectors to chelating with three zinc(II) cations while the zinc(II) cations coordinate with three HPIDC^2 − anions, to form the T-shape molecular building blocks [Zn_n(HPIDC)_n], which further connect in interdigitating or alternating fashion to result in the assembly of two different 3,3-connected networks. The luminescence behaviors and solvent effect were also discussed.     

Hydrothermal syntheses and characterization of a series of mixed-ligand luminescent CdII frameworks with novel 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl) acetate ligand and benzenedicarboxylate isomers

Under similar hydrothermal synthetic conditions using a novel flexible ligand 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)acetonitrile (PPAN), benzenedicarboxylate isomers (H₂pa = phthalate, H₂ip = isophthalate, and H₂tp = terephthalate) and Cadmium(II) acetate, three novel mixed-ligand Cd(II) coordination polymers {[Cd₂(PPAA)₂(μ-pa)(H₂O)]·2H₂O}_n (1), {[Cd₄(PPAA)₄ (μ₄-ip)₂]·2H₂O}_n (2) and {[Cd₂(PPAA)₂(μ-tp)]·2H₂O}_n (3) (PPAA⁻ = 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl) acetate) have been isolated, in 1–3 PPAN, and are also hydrolyzed into a novel PPAA⁻ ligand. Complex 1 is a 1D coordination polymer in which the tetra-nuclear [Cd₄(PPAA)₄]^4 + structural units are extended by tri-dentate μ-pa^2 − ligands. Complex 2 contains binuclear [Cd₂(PPAA)₂]^4 + structural units, which are extended by four tetra-dentate μ₄-ip^2 − ligands to link eight neighboring binuclear [Cd₂(PPAA)₂]^4 + units ultimately forming a 2D layered framework, while complex 3 contains 1D double chain containing [Cd(PPAA)]_n cation structural units, which are further extended by tetradentate μ-tp^2 − ligands to form a new 2D layered framework. All the complexes have been investigated by elemental analysis, FT-IR, thermal analysis and fluorescence characterization. The flexible coordination modes of PPAA⁻ are also briefly analyzed. The flexible coordination modes of PPAA⁻ and benzenedicarboxylate isomers also reveal great potential in the construction of these novel mixed-ligand luminescent frameworks with diverse structural motifs and unique functional properties.     

Dual-nodal PMMA-supported Eu3 +-containing metallopolymer with high color-purity red luminescence

Based on chemical grafting of the complex monomer [Eu(TTA)₃(4-vinyl-Py)₂] (HTTA = 2-thenoyltrifluoroacetylacetate, 4-vinyl-Py = 4-vinyl-pyridine) with two active vinyl groups and MMA (methyl methacrylate), the dual-nodal PMMA-supported metallopolymers with high color-purity Eu^3 +-based luminescence are obtained. The physical properties show that their luminescent properties (τ_obs = 494–552 μs and Ф_Eu^L = 50–55%) are distinctively enhanced from copolymerization in comparison with those (τ_obs = 470 μs and Ф_Eu^L = 44%) of the complex monomer besides the improvement of thermal-stabilities.     

One novel and unprecedented one-dimensional zinc coordination polymer with a N,O-donor chelating phenolic ligand, 3-n-butyl-2-(2-hydroxyphenyl)-3H-benzimidazole: synthesis,structure, characterization,photoluminescence and theoretical calculations

One novel and unprecedented 1D zinc coordination polymer with an unsymmetrical N,O-donor phenolic ligand, [Zn(bpbm)₂]_n (1) (Hbpbm · HCl · H₂O = 3-n-butyl-2-(2-hydroxyphenyl)-3H-benzimidazole hydrochloride hydrate) has been prepared and characterized crystallographically, and the geometric structure and photoluminescent properties, investigated experimentally and theoretically by DFT level. The deprotonated ligands, bpbm^?, as μ₂-bridging, adopt uncommon (O,N)-bridging poly(oligo)merization coordination mode, and not the common O-bridging poly(oligo)merization coordination mode. The photoluminescent property is assigned to π → π¹ ligand-to-ligand charge transfer transition (LLCT).     

Oxidation of vanillin by peroxomonosulphate-thermodynamic and kinetic investigation

The oxidation of vanillin by peroxomonosulphate (PMS) in acetic acid–sodium acetate buffered medium was carried out at 308 K. The rate was first order with respect to [vanillin] and [PMS]. The rate increased with increase in pH and the rate was too fast to be measured at pH 5.2. The rate increased with increase in [acetate] and the plot of k_obs versus [acetate] was a straight line with positive intercept. Variation of ionic strength had no effect on the rate of the reaction. Effects of polarity were studied with five different solvents and in all the cases, log k_obs versus 1/? were linear with negative slope. The reaction had been carried out at four different temperatures and the activation and thermodynamic parameters were calculated. The product of oxidation was confirmed as vanillic acid by IR, ¹H NMR and GC-MS spectral analysis. Based on the results obtained a reaction scheme had been proposed and the rate law was derived.     

Biotribological performance of NCD coated Si3N4–bioglass composites

A nanocrystalline diamond (NCD) coated Si₃N₄–bioglass composite, with potential use for hip and knee joint implants, was tribologically tested in simulated physiological fluids. NCD was deposited using a hot-filament chemical vapour deposition (HFCVD) apparatus in an Ar–H₂–CH₄ gas mixture. Self-mated reciprocating experiments were performed using a pin-on-flat geometry in Hanks' balanced salt solution (HBSS) and dilute fetal bovine serum (FBS). A nominal contact pressure of 25 MPa was applied for up to 500,000 cycles. Very low friction coefficients of 0.01–0.02 were measured using HBSS, while for FBS lubricated tests the values are slightly higher (0.06–0.09), due to a protein attaching effect. AFM assessed wear rates by an approach using the bearing function for volume loss quantification, yielding wear rates of k ∼ 10^− 10 mm³ N^− 1 m^− 1 in HBSS and k ∼ 10^− 9–10^− 8 mm³ N^− 1 m^− 1 for FBS, characteristic of very mild wear regimes.     

Mononuclear Dy(III) complex based on bipyridyl-tetrazolate ligand with field-induced single-ion magnet behavior and luminescent properties

A new mononuclear Dy(III) complex, namely {[Dy(tbpy)₂(NO₃)(DMF)]⋅ DMF} (1) (tbpy = 6-(tetrazol-5-yl)-2,2′-bipyridine, DMF = N,N-dimethylformamide), has been synthesized and characterized. Structural measurements reveal that the Dy(III) ion displays a distorted tricapped trigonal prism with two mono-anionic tridentate chelating ligands, nitrate anion and N,N-dimethylformamide molecule. Magnetic investigation indicates that the title complex 1 exhibits field-induced single-ion magnet behavior. Moreover, the studies on photoluminescence properties show that complex 1 displays relatively strong fluorescent emission, which are typical narrow emission bands of lanthanide ion.     

A highly electrical conducting, 3D supermolecular Ag(I) coordination polymer material with luminescent properties

A stable, 3D supermolecular material, [Ag(H₂O)(2,6-ndc)_0.5(L)_0.5]_n (2,6-H₂ndc = 2,6-naphthalenedicarboxylic acid; L = N,N′-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide (dpndi)) with high electrical conducting ability was successfully synthesized under a solvothermal condition and characterized by single-crystal X-ray diffraction, IR spectroscopy and thermogravimetric analysis (TGA). The electrical conducting and photoluminescence properties were investigated.     

Reduction of N2O by NH3 on polycrystalline copper and Cu(1 1 0): A combined XPS,FT-IRRAS and kinetics investigation

Kinetics of N₂O decomposition and catalytic reduction of N₂O by NH₃ in the presence or absence of oxygen have been studied on polycrystalline Cu planar chip (3 cm × 3 cm × 0.1 cm) or Cu(1 1 0) single crystal, using catalytic test equipment, XPS and FT-IRRAS techniques. It has been shown that N₂O decomposes on metallic Cu, but gives then Cu₂O, which is detrimental to N₂O decomposition. The presence of a reductant, such as NH₃, allowed N₂O to react leading to its catalytic reduction to N₂; 500 °C is the best temperature for catalytic reduction alone, i.e. with low additional self-decomposition of N₂O or NH₃. The presence of oxygen, in amount less than that of NH₃, leads to more efficient NH₃ oxidation, oxygen being observed to be more reactive than N₂O on NH₃. XPS results enabled to identify the active surface as metallic Cu and Cu₃N for NH₃ oxidation and NH₂, NH, N adsorbed species as intermediates of the reaction. At room temperature, in the presence of N₂O, O₂ and NH₃, FT-IRRAS allowed to show the formation of NH₂ and NH species (bands at 1550 and 1440 cm⁻¹, respectively) and of two N₂^δ− species (bands at 2170 and 2204 cm⁻¹), the latter one corresponding to adsorbed N₂^δ− species close to adsorbed electron accepting O or OH species. This study demonstrated that N₂O decomposed to N₂ and O species during SCR reaction; it enabled to identify several adsorbed surface species (N, NH, NH₂, N₂^δ−), both by XPS after catalytic reaction at 500 °C on the polycrystalline Cu chip and by IRRAS on Cu(1 1 0) single crystal in the presence of the reactants at room temperature. In addition, it was shown that N₂ is a powerful IR probe to characterise the surrounding environment of surface sites that cannot be identified by any other way.     

Bi-Co3O4 catalyzing N2O decomposition with strong resistance to CO2

Bi added to Co₃O₄ by coprecipitation method significantly decreased the average crystalline size of Co₃O₄ and increased the surface area and the active sites of the catalyst in population for catalyzing the N₂O decomposition. Over Bi_0.02Co that was the optimized from the Bi_xCo catalysts, 2000 ppm of N₂O in pure Ar was completely decomposed at 400 °C in GHSV of 20,000 h^− 1. Outstandingly, the catalyst exhibited a strong resistance to CO₂, stable N₂O conversion larger than 95% was obtained over the catalyst in the presence of 10% CO₂ at the reaction temperature.     

Property improvement of 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb0.96La0.04(ZrxTi1−x)0.99O3 ceramics by hot-pressing

The piezoelectric ceramics of the compositions expressed by the formula: 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb_0.96La_0.04(Zr_xTi_1−x)_0.99O₃ (x = 0.50–0.53) were prepared by two kind of sintering processes: conventional sintering (CS) and hot-pressing (HP) sintering. By comparing the properties of these two series of ceramics, piezoelectric coefficients (d₃₃), electromechanical coupling factors (k_p), dielectric constants (ɛ_r), etc. were enormously improved by HP sinter procedure, which can be attributed to the highly dense microstructure (bulk density >99%). The most impressive results are the d₃₃ (845pC/N) and k_p (0.703) in the HP specimen with Zr/Ti = 51/49, which have not been observed in the previous relative reports. Additionally, according to the contrast of the experiment data, the origin of the property improvement was analyzed in details.     

Copper(II) azide complexes of [Cu(acac)(N3)(dpyam)] and [Cu(μ-N3-κN1)(C2N3-κN1)(dpyam)]2: Synthesis,crystal structure and magnetism

Two new compounds, [Cu(acac)(N₃)(dpyam)] (1), (acac = acetylacetonate; dpyam = di-2-pyridylamine) and [Cu(μ-N₃-κ^N1)(C₂N₃- κ^N1) (dpyam)]₂ (2), have been synthesized and characterized by single-crystal X-ray diffraction and magnetic analyses. Compound 1 is a mononuclear compound in which each of two independent Cu(II) ions is penta-coordinated with a distorted square pyramidal geometry with distortion parameters τ = 0.21 and 0.16. In contrast, compound 2 is an azido-bridged dinuclear compound with monodentate dicyanamide anions and the Cu(II) ions display a distorted trigonal bipyramidal geometry with τ = 0.73 and end-on azido bridges providing an equatorial–axial position between the metal ions. The EPR spectra of powdered samples for 1 and 2 have also been investigated. Magnetic susceptibility measurements of compound 2 reveal a very weak ferromagnetic interaction between the Cu(II) ions with a J value of +5.8 cm⁻¹.     

Highly active SO2-resistant ex-framework FeMFI catalysts for direct N2O decomposition

Ex-framework FeMFI catalysts, prepared by isomorphous substitution of iron in the aluminosilicate or gallosilicate MFI-type framework and activation by calcination at 823 K and steaming (300 mbar H₂O in N₂) at 873 K, show high activity and stability in N₂O decomposition in the presence of O₂, CO₂, H₂O, and SO₂. The N₂O conversion of the ex-framework catalysts in simulated tail-gas mixtures was >80% at 800 K and 75,000 h⁻¹. The specific activity per mole of Fe (turnover frequency, TOF) of the ex-framework catalysts in N₂O–He is four to nine times higher than observed for catalysts prepared by conventional solid and liquid-ion exchange, and sublimation methods. The stability of ex-framework catalysts for the direct N₂O decomposition, in the absence of any reductant, is remarkable, showing no significant deactivation (at N₂O conversion levels ranging from 20 to 65%) after 600 h on stream. Sublimed and especially ion-exchanged FeZSM-5 catalysts show a strong irreversible deactivation in feed mixtures containing H₂O and SO₂. The effect of SO₂ on the catalytic performance of FeMFI catalysts is discussed, as well as the applicability of the ex-framework FeMFI catalysts in fluid-bed combustion facilities.     

Crystal structure and magnetic property of a 3D heterometallic coordination polymer constructed by 3-cyanobenzoate and 3-(5H-tetrazol) benzoate ligands

Hydrothermal reaction of Cd(NO₃)₂, Co(NO₃)₂, Na(3-cba) and NaN₃ yielded a 3D heterometallic coordination polymer, [Cd(μ₅-3-tzba)(μ₂-3-cba)(μ₃-OH)Co(H₂O)]_n·2nH₂O 1 (3-H₂tzba = 3-(5H-tetrazol)benzoic acid and 3-Hcba = 3-cyanobenzoic acid), which was characterized by single-crystal X-ray diffraction. The in situ [2 + 3] cycloaddition reaction of nitrile and azide in presence of Cd(II) salt afforded tetrazolate-based 3-tzba^2? ligand. In 1, metal-oxo chains [Cd(μ₃-OH)Co]_n are linked by 3-tzba^2? in an unprecedented μ₅-κN1:κN2:κN3:κN4:κO1,O2 coordination mode to form 2D layers, which are further pillared by 3-cba^? to generate a 3D open framework encapsulating 1D chiral channels. Variable-temperature magnetic studies show that 1 exhibits antiferromagnetic interactions between Co(II) ions bridged by μ₃-OH group.