Photoluminescence and structural characteristics of double tungstates A(M1−X PrX)W2O8 (A = Li,Cs, M = Al,Sc, La)

In this article, photoluminescence of Pr³⁺ ions in the double tungstate A(M_1?X Pr_X)W₂O₈ (A = Li, Cs, M = Al, Sc, La; 0.0 ≤ X ≤ 0.1) are characterised. By varying ion radius in A and M sites the crystal structure was modified and even in crystals with similar structural characteristics three distinctive types of luminescence are observed. When the substitution ions in both A and M sites are relatively small the host lattice exhibits luminescence dominantly. With the small A site ion (Li⁺) and the large M site ion (La³⁺, 1.03 Å) the Pr³⁺ ion exhibits prominent luminescence. With the very large A site ion (Cs⁺, 1.67 Å) and relatively small M site ion (Sc³⁺, 0.75 Å) the Pr³⁺ exhibits both the 4f²–4f5d excitation and the ³P_J manifold excitations in the absorption spectrum. These excitation levels lead to two strong emissions from the Pr³⁺. PL characteristics are discussed with respect to crystal structural criteria.     

Synthesis of La1−xSrxMO3 (M = Mn,Fe, Co,Ni) nanopowders by alanine-combustion technique

La_1?xSr_xMO₃ (M = Mn, Fe, Co, Ni, x = 0–0.3) powders were obtained by solution combustion technique using metal nitrates and α-alanine. The as-prepared powders, resulted by the combustion reaction, were annealed at different temperatures to investigate the evolution of crystalline phases. For the strontium-doped lanthanum-based perovskites, higher annealing temperatures than for the corresponding pure lanthanum-based perovskites are needed to obtain single-phase compounds depending on M-site metal and strontium content. The oxide powders were investigated by FT-IR spectra, X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific area measurements. Based on our results we propose different mechanisms for La_1?xSr_xMO₃ (M = Mn, Fe, Ni, x = 0–0.3) obtaining, depending on the intermediary compounds formed in the combustion reaction or during the thermal treatment of the as-prepared powders.     

Divalent metal complexes of formylhydrazine: Syntheses and crystal structures of M(CH4N2O)2(H2O)2·2NO3 (M = Zn,Co)

The syntheses and crystal structures of Zn(CH₄N₂O)₂(H₂O)₂·2(NO₃) (1) and Co(CH₄N₂O)₂(H₂O)₂·2(NO₃) (2), the first well-characterised metal complexes of formylhydrazine (fh), are described. In both compounds, the fh acts as an N,O-bidentate ligand in a centrosymmetric [M(fh)₂(H₂O)₂]²⁺ cation, with charge balance supplied by nitrate counter ions. The packing for the two compounds are quite different: in 1, chains of [Zn(fh)₂(H₂O)₂]²⁺ units are seen in the triclinic unit cell, whereas in the monoclinic structure of 2, sheets of cations occur. This might arise because the conformations of the five-membered chelate rings for the ligands are slightly different, with that for 2 showing a greater degree of puckering.     

Synthesis,structure, and electrochemical behavior of a new dinuclear Rh(III) complex bridged by a bpp− ligand (bpp− = 3,5-bis(2-pyridyl)pyrazolate)

The new dinuclear rhodium complex [(Cp*RhCl)₂(bpp)](PF₆) ([1](PF₆), Cp* = pentamethylcyclopentadienyl, bpp = 3,5-bis(2-pyridyl)pyrazolate) was synthesized by the reaction of [Cp*RhCl₂]₂ with 3,5-bis(2-pyridyl)pyrazole (bppH). [1](PF₆) was characterized by ¹H- and ¹³C{¹H}-NMR spectroscopy and X-ray diffraction. The distance between the two Rh atoms in [1](PF₆) is 4.746(3) Å. A cyclic voltammogram of [1](PF₆) in acetonitrile shows three-step reduction peaks at E_pc = − 1.44, − 1.68 and − 1.88 V (vs. Fc⁺/Fc), which are assigned to the reduction of the two Rh(III) centers and the bpp⁻ ligand, respectively. [1](PF₆) catalyzes the reduction reaction of NAD⁺ (nicotinamide adenine dinucleotide) using HCO₂⁻ as a reductant.     

One-step preparation of Pt–M@FP-MWNT catalysts (M = Ru,Ni, Co,Sn, and Au) by γ-ray irradiation and their catalytic efficiency for CO and MeOH

Pt–M@FP-MWNT catalysts (M = Ru, Ni, Co, Sn, and Au) were prepared by one-step γ-ray irradiation. Two different types of functional polymers (FP), such as poly(vinylphenyl boronic acid) (PVPBAc) and poly(vinylpyrorridone) (PVP), were used as anchoring agents, when Pt–M nanoparticles were deposited on the multi-walled carbon nanotube (MWNT) using γ-ray irradiation in aqueous solution at room temperature. The obtained Pt–M@FP-MWNT catalysts were then characterized by XRD, TEM, and elemental analysis. The catalytic efficiency of the Pt–M@FP-MWNT catalysts was examined for CO stripping and MeOH oxidation for use in a direct methanol fuel cell (DMFC). The catalytic efficiency of the Pt–M@FP-MWNT catalyst for MeOH oxidation follows this order: Pt–Sn@FP-MWNT > Pt–Co@FP-MWNT > Pt–Ru@FP-MWNT > Pt–Au@FP-MWNT > Pt–Ni@FP-MWNT catalysts. The CO adsorption capacity of the Pt–M@FP-MWNT catalyst for CO stripping is as follows: Pt–Ru@FP-MWNT > Pt–Sn@FP-MWNT > Pt–Au@FP-MWNT > Pt–Co@FP-MWNT > Pt–Ni@FP-MWNT catalyst.     

Synthesis,crystal structures and properties of two coordination polymers constructed from M2+ (M2+ = Zn2+, Ni2+) with methylenediisophthalic acid and 1,1′-(1,4-butanediyl)bis(imidazole)

Two coordination polymers [Zn₂(H₂L)₂(bbi)(H₂O)₂·H₂O]_n 1 and [Ni₄(L)₂(bbi)₂(H₂O)₄·H₂O]_n 2 {H₄L = methylenediisophthalic acid, bbi = 1,1′-(1,4-butanediyl)bis(imidazole)} have been prepared under hydrothermal conditions and structurally characterized by X-ray diffraction analyses. Mononuclear 1 is a 1D ladder chain and bbi adopts trans-configuration linking two metal centers. Plus the hydrogen binding interactions, it formed a 3D two-fold perpendicular interpenetrating (4, 5)-connected framework. Binuclear units of 2 are connected by L^4? and cis-bbi to generate a 3D (4, 6)-connected framework, in which twisted bbi with binuclear units generate the rare triflexure helix. In solid state, complex 1 exhibits yellowgreen emissions at ambient temperature. Magnetic measurements show that there exist weak ferromagnetic interactions in 2.     

Selective acetylation of glycerol over CeO2–M and SO42−/CeO2–M (M = ZrO2 and Al2O3) catalysts for synthesis of bioadditives

The feasibility of acetylation of glycerol with acetic acid was investigated employing CeO₂–ZrO₂, CeO₂–Al₂O₃, SO₄^2?/CeO₂–ZrO₂, and SO₄^2?/CeO₂–Al₂O₃ solid acid catalysts to synthesize monoacetin, diacetin and triacetin having interesting applications as bioadditives for petroleum fuels. Intensive physicochemical and surface characterization of the prepared catalysts were performed using XRD, BET surface area, ammonia-TPD and Raman spectroscopy techniques. Characterization results revealed that impregnated sulfate ions strongly influence the physicochemical characteristics of the investigated mixed oxide catalysts. Among various catalysts investigated, the SO₄^2?/CeO₂–ZrO₂ combination catalyst exhibited superior catalytic activity under mild conditions. The effect of various parameters such as reaction temperature, molar ratio of acetic acid to glycerol, catalyst wt% and time-on-stream were studied over the SO₄^2?/CeO₂–ZrO₂ catalyst to optimize the reaction conditions. Catalyst reusability was also carried out to understand its stability.     

Three unique MOFs constructed by 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene and dicarboxylates: From rhombic tetrameric zinc(II) 2D layer to 2D + 2D → 3D polycatenated frameworks

Three metal–organic networks, namely, [Zn₂(Hnip)(4-bpdb)(nip)₂(μ₃-OH)] (1), {[Zn(tbip)(4-bpdb)_1.5]·CH₃OH}_n (2), and {[Ni(1,3-bdc)(4-bpdb)]·2H₂O}_n (3) (4-bpdb = 1.4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, H₂nip = 5-nitroisophthalic acid, H₂tbip = 5-tert-butylisophthalic acid, and 1,3-H₂bdc = 1,3-benzenedicarboxylic acid) are synthesized under hydrothermal conditions. The structure of 1 is built around uncommon rhombic {Zn₄} clusters with double T_d and double O_h Zn(II) geometries, which extend into a 2D network by the rigid deprotonated H₂nip and 4-bpdb bridges. Meanwhile, 2 presents a novel 2D → 3D parallel polycatenated framework assembled from 2D bilayers with cuboids as the fundamental building units. Compound 3 features an interesting 2D → 3D inclined polycatenated network based on 4⁴-sql subunits. Moreover, the thermal stabilities, photoluminescence, and magnetic properties of the compounds are also discussed.     

Effects of different glass formers on Li2S–P2S5–MS2 (M = Si,Ge, Sn) chalcogenide solid-state electrolytes

Chalcogenide solid-state electrolytes (SSEs) have been receiving growing attentions due to their high ionic conductivity and suitable mechanic properties, especially the Li₂S–P₂S₅ systems incorporated with a second glass network formers (Si, Ge, Sn, and so on) besides P. Although the ionic conductivities are generally enhanced with the second glass network formers, the comprehensive effects of different glass formers on other properties, including electrochemical, cycling, and air stability, remain elusive. To acquire deeper understanding, herein, three common but representative glass network formers (SiS₂, GeS₂, and SnS₂) were introduced into Li₂S–P₂S₅, and their individual effects were investigated systematically. The results of multiscale characterizations before and after lithium stripping/plating cycling confirmed that the introduction of metal cations (Ge, Sn) generally leads to worse electrochemical stability and shorter cycle life of these SSEs toward lithium metal compared with SSEs with nonmetal cation (Si) modification. However, the air stability is related to the binding energy of M–S (M = Si, Ge, Sn), which is consistent with the hard base soft acid theory. This work provides valuable understanding for designing pragmatic Li₂S–P₂S₅–MS₂-based SSEs with high electrochemistry, cycling, and air stability.     

Two 1-D Krebs-type heteropolyoxotungstates based on [X2W21O72Na(OH)2]13 − (X = SbIII,BiIII) units

By the one-pot self-assembly reaction of simple materials under acidic aqueous solution, two 1-D chain Krebs-type heteropolyoxometalates [H₂N(CH₃)₂]₂Na₁₁[X₂W₂₁NaO₇₂(OH)₂]·34H₂O (X = Sb^III for 1, Bi^III for 2) have been successfully synthesized and structurally characterized by elemental analysis, IR spectra, UV spectra, thermogravimetric (TG) analysis and X-ray single-crystal diffraction. The most prominent structural feature of 1 and 2 is that both display an interesting 1-D chain alignment constructed from Krebs-type [X₂W₂₁NaO₇₂(OH)₂]^13 − fragments connected by sharing four W–O–W connectors, which is for the first time observed in the polyoxometalate chemistry. Additionally, the electrochemical properties of 1 and 2 have been studied in 0.5 mol L^− 1 Na₂SO₄ + H₂SO₄ supporting electrolyte.     

Electronic properties and stability of M2O3 (M = Al,Ga, In) and alloy (MxGa1-x)2O3 in α and β phases: A theoretical study

Ga₂O₃ is clearly emerging as an important wide band-gap semiconductor. Band-gap engineering is now highly demanded for expanding its applications. Alloying with the same group of metal oxides is a straightforward and effective way. In this work, by using hybrid density functional theory calculations, the structural, electronic properties, and phase stability of group IIIA (Al, Ga, In) metal oxides and their ternary alloys (M_xGa_1-x)₂O₃ (M = Al, In) in the corundum and monoclinic phases are systematically investigated. The lattice constants, elastic constants, modulus, formation energies, band-gaps, band-gap deformation potentials, band-edge alignments, band-gap bowing, and ternary alloy formation energies are obtained. The basic relations between the geometric structure and electronic properties are discussed. It is found that the cation ordered structure is the most stable alloy structure in the monoclinic phase, rather than the random alloy structure as is commonly thought. A phase stability diagram of the (M_xGa_1-x)₂O₃ alloys is established, showing that the stable phase of the alloy changes from the monoclinic phase to the corundum phase when the incorporation of Al₂O₃ (In₂O₃) is greater than 69% (76%). These results can be used to understand the relative experimental data and shed some light on the synthesis and device design efforts of Ga₂O₃.     

Characterization of Ba0.5Sr0.5M1−xFexO3−δ (M = Co and Cu) perovskite oxide cathode materials for intermediate temperature solid oxide fuel cells

Ba_0.5Sr_0.5Co_1?xFe_xO_3?δ (x = 0.2, 0.6, and 0.8) and Ba_0.5Sr_0.5Cu_1?xFe_xO_3?δ (x = 0.6 and 0.8) perovskite oxides have been investigated as cathode materials for intermediate temperature solid oxide fuel cells. All the samples synthesized by a citrate–EDTA complexing method were single-phase cubic perovskite solid solutions. Then, the thermal expansion coefficient, electrical conductivities, the oxygen vacancy concentrations, the polarization resistances (R_p), and the power densities were measured. An increase in the Co content resulted in a decrease in the polarization resistance, the electrical conductivities at low temperatures, and the inflection point of the thermal expansion coefficient, but it led to an increase in the electrical conductivities at high temperatures, the oxygen vacancy concentrations, and the maximum power densities. The Cu-based system has similar behavior to the Co-based system; yet, in terms of the electrical conductivities, high Cu content gave a better result than low content for the entire range of temperatures.     

The adsorption feature and photocatalytic oxidation activity of K1−2xMxTiNbO5 (M = Mn,Ni) for methyl mercaptan in methane

The novel photocatalytic ceramics material K_1?2xM_xTiNbO₅ (M = Mn, Ni) were prepared through Mn²⁺ and Ni²⁺ ion-exchange of KTiNbO₅, which was synthesized by a hydrothermal method. The influence of the ion-exchange process on the structure and morphology of prepared ceramics material were investigated by such physicochemical methods as powder X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), UV–visible diffuse reflectance spectroscopy (UV–vis DRS) and Fourier-transform infrared (FT-IR) microscopy. The adsorption and photocatalytic oxidation of methyl mercaptan (MM) in methane were used to evaluate the catalytic performance of different constitutes. The results revealed that K_1?2xNi_xTiNbO₅ exhibited better adsorption and photocatalytic oxidation activity for MM in methane under both visible and UV light radiation. While the photocatalytic oxidation activity of K_1?2xMn_xTiNbO₅ is similar to that of K_1?2xNi_xTiNbO₅, however it has little adsorption activity for MM in dynamic state.     

Redox properties of α2-K8P2W17(M·OH2)O61 (M = MnII,ZnII, FeII,CoII, and NiII) Wells–Dawson heteropolyacids probed by scanning tunneling microscopy and tunneling spectroscopy

Scanning tunneling microscopy (STM) and tunneling spectroscopy investigations of α₂-K₈P₂W₁₇(M·OH₂)O₆₁ (M = Mn^II, Zn^II, Fe^II, Co^II, and Ni^II) Wells–Dawson heteropolyacids (HPAs) were conducted. HPAs formed self-assembled and well-ordered arrays on graphite surface. Negative differential resistance (NDR) phenomena were observed in the tunneling spectra of the HPAs. NDR peak voltage of the HPAs appeared at less negative voltage with increasing reduction potential and with decreasing UV–visible absorption edge energy. HPAs were then applied to the electro-oxidation of methanol as a redox mediator. The oxidation activity for residual intermediates in the reaction increased as NDR peak voltage of HPA appeared at less negative voltage.     

Se4CuX,Te4CuX and Cu2Se7X2 (X = GaCl4) — Coordination compounds of neutral infinite chalcogen chains

The reactions of selenium and tellurium in molten GaCl₃ with SbCl₃ and copper(II) or copper(I) chloride yielded CuSe₄[GaCl₄] (1), CuTe₄[GaCl₄] (2), and Cu₂Se₇[GaCl₄]₂ (3). EPR measurements show no resonances, implying the presence of monovalent Cu ions. The structures consist of discrete infinite neutral chalcogen chains of helical shape. Cu(I) ions are coordinated to the Se and Te chains via three chalcogen atoms for the isotypic 1 and 2, and via two Se atoms for 3. The coordination tetrahedron for Cu is completed by coordination of Cl atoms of neighboring [GaCl₄]⁻ anions.     

Dual regulation of Li+ migration of Li6.4La3Zr1.4M0.6O12 (M = Sb,Ta, Nb) by bottleneck size and bond length of M−O

Bottleneck size is the minimum Li⁺ migration channel of Li₇La₃Zr₂O₁₂ (LLZO) and it greatly influences the Li⁺ conductivity. Doping different elements on the Zr site of LLZO can adjust the bottleneck size and improve the Li⁺ conductivity. However, the regulation mechanism is not clear. In this work, Li_6.4La₃Zr_1.4M_0.6O₁₂ (M = Sb, Ta, Nb) has been prepared and the bottleneck size has been adjusted by doping different pentavalent ions. The results manifest that the cell parameter and bottleneck size decrease with the rise of the radius of doped pentavalent ions. This is because larger pentavalent ion leads to larger bond length of M–O, and weaker covalent component between M⁵⁺ and O^2-, corresponding, the formal charge on the M⁵⁺ become larger, and the bond length of La–O slightly decreases due to the coulomb repulsion between La³⁺ and M⁵⁺ increase. While, the activation energy drop firstly and then rise with the rise of bottleneck size because of the migration of Li⁺ not only relate to the size of the migration channel but also to the strength of M–O covalent bonding. The bottleneck size and bond length of M–O synergistically affect the migration of Li⁺.     

Synthesis and optical properties of Ce0.95Pr0.05−xMxO2 (M = Mn,Si) as potential ecological red pigments for coloration of plastics

Ecological red pigments Ce_0.95Pr_0.05?xM_xO₂ (M = Mn, Si) have been synthesized by conventional solid-state route and characterized by X-ray diffractometer, scanning electron microscope and UV–vis spectroscopy. Mn⁴⁺/Si⁴⁺ was incorporated into the CeO₂–PrO₂ system to tune the color properties of the pigments by shifting the optical absorption edge. Si⁴⁺ substitution blue shifts the absorption edge of Pr-doped ceria and shows bright reddish brown color. Mn⁴⁺ substitution stabilizes the absorption edge and exhibits dark brown hue. The coloring mechanism is based on the shift of charge transfer band of CeO₂ to higher wavelength by co-substitution of Pr⁴⁺ and tetravalent metal ions in ceria. Si co-doped pigments possess smaller particles and hence exhibit more lightness compared to Mn co-doped samples. The reddish brown pigments exhibit very good coloring performance in polymer matrix. These Ce_0.95Pr_0.05?xM_xO₂ (M = Mn, Si) pigments have potential to be used as ecological red pigments for coloration of plastics.     

Synthesis and characterization of nitrosyl complexes containing 4,6-dimethyl-pyrimidine-2-thiolato (‘SpymMe2’) as ligand: [Ru(‘SpymMe2’,-N,-S) (‘SpymMe2’,-S)(NO)(P–P)](PF6) (P–P = 1,2-bis(diphenylphosphino)ethane or 1,2-bis(diphenylphosphino)ethylene: X-ray structure of [Ru(‘SpymMe2’,-N,-S) (‘SpymMe2’,-S)(NO)(dppe)](PF6)

The reaction products of fac-[RuCl₃(NO)(P–P)], [P–P = dppe (1) and c-dppen (2)] with the 4,6-dimethyl-2-mercaptopyrimidine ligand in methanol are the correspondent nitrosyl derivatives [Ru(‘SpymMe₂’,-N,-S)(‘SpymMe₂’,-S)(NO)(P–P)](PF₆). These are the first reported ruthenium complexes containing both, nitrosyl and a pyrimidinethiol derivative. The X-ray crystal structure of complex 1 is reported. The intense ν_NO bands in the IR spectra (KBr pellets) of complexes 1 and 2 are at 1850 and 1860 cm⁻¹, respectively. The cyclic voltammetry of both complexes shows two reduction waves centered at the NO⁺ ligand.     

Synthesis,crystal structure,and thermal stability of a novel 3D cadmium carboxyphosphonate containing left-hand helical chains Cd3Cl2[(O3PCH2–N(H)C5H9–COO)2(H2O)2] · 4H2O

A novel 3D cadmium carboxyphosphonate containing left-hand helical chains, Cd₃Cl₂[(O₃PCH₂–N(H)C₅H₉–COO)₂(H₂O)₂] · 4H₂O 1 has been synthesized by hydrothermal reaction at 120 °C and structurally characterized by single-crystal X-ray diffraction as well as with infrared spectroscopy, elemental analysis and thermogravimetric analysis. In compound 1, the hexanuclear clusters based on Cd(1)O₄Cl₂, Cd(2)O₄Cl₂, Cd(3)O₆ and CPO₃ polyhedra are interconnected through carboxyphosphonate ligands to form a 3D open-framework structure with channel system. The result of connections in this manner is the formation of 20- and 30-atom rings that are parallel to one another and run in the a-axis direction. It is interesting that a type of left-hand helical chain is formed by HL^2? ligands bridging Cd₃ ions running along the b-axis.