Octahedral Form Research Articles

Oxo-Hydroxoferrate K2-x Fe4O7-x (OH) x : Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures.

The reaction of Fe(NO3)3⋅9 H2O with KOH under hydroflux conditions at about 200 °C produces red crystals of K2−xFe4O7−x(OH)x in a quantitative yield. In the crystal structure, edge‐sharing [FeO6] octahedra form ∞2[ Fe2O6] honeycomb nets. Pillars consisting of pairs of vertex‐sharing [FeO4] tetrahedra link the honeycomb layers and form columnar halls in which the potassium ions are located. The trigonal (P 3‾ 1m) and the hexagonal (P63/mcm) polytypes of K2−xFe4O7−x(OH)x show oriented intergrowth. The sub‐stoichiometric potassium content (x≈0.3) is compensated by hydroxide ions. K2−xFe4O7−x(OH)x is an antiferromagnet above 2 K and its magnetic structure was determined by neutron powder diffraction. Under ambient conditions, K2−xFe4O7−x(OH)x hydrolyzes and K2CO3 ⋅ H2O forms gradually on the surface of the K2−xFe4O7−x(OH)x crystals. Upon annealing at air at about 500 °C, the potassium atoms in the columnar halls start to order into a superstructure. The thermal decomposition of K2−xFe4O7−x(OH)x proceeds via a topotactic transformation into K1+x′Fe11O17, adopting the rhombohedral β’’ or the hexagonal β‐aluminate‐type structure, before γ‐Fe2O3 is formed above 950 °C, which then converts into thermodynamically stable α‐Fe2O3.

Synthesis, characterization, and pharmacological evaluation of the proton transfer salts of 2-aminobenzothiazole derivatives with 5-sulfosalicylic acid and their Cu(II) complexes

Two proton transfer compounds, formed between 2-aminobenzothiazole derivatives (2-aminobenzothiazole (abt) and 2-amino-6-ethoxybenzothiazole (EtOabt)) and 5-sulfosalicylic acid dihydrate (H3ssa) as parent compounds, (Habt)+(H2ssa)− (1) and (HEtOabt)+(H2ssa)− (2) and their Cu(II) complexes (3 and 4, respectively) have been prepared and characterized using spectroscopic techniques. The single crystal X-ray diffraction method has been also applied to 3 and 4. Although 3 has a distorted octahedral form, 4 exhibits a distorted square pyramidal geometry. All compounds, including saline and diclofenac sodium as standards, have been evaluated pharmacologically for their anti-inflammatory and analgesic activities in rats and mice. Parent compounds (abt, EtOabt, and H3ssa) 3 and 4 show significant anti-inflammatory and analgesic activities as compared with control compounds.

Controllable synthesis of LiNbO3 micro-octahedrons and micro-cubes via a molten-salt process

In this paper, a facile molten-salt strategy is developed for controllably synthesizing LiNbO3 microcrystals shaped as octahedrons and cubes in molten LiNO3 and LiCl salts without using any capping agents. The as-prepared LiNbO3 micro-octahedrons and micro-cubes are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). Our results show that the formation of LiNbO3 micro-octahedrons and micro-cubes can be attributed to a dissolution-nucleation-aggregation-recrystallization process. Furthermore, in order to minimize the surface and interface energies between the constituents and the salts, octahedral and cubic morphology forms under different molten-salt conditions, which shows the anion may play a crucial role in tuning the product morphology.

Ab-initio studies of electronic, structural and thermophysical properties of the Sr2TiMoO6 double perovskite

Double perovskite-like material Sr2TiMoO6 (STMO) has been obtained by solid state synthesis. Analysis of the morphology by SEM reveals the occurrence of polyhedral grains with octahedral forms in its faces and hexahedron forms in the corners. The electronic structure and thermophysical properties are reported for the first time using the pseudopotential and plane-wave method. Theoretical calculations for different antiferromagnetic configurations showed that the antiferromagnetic spins alignment in planes interspersed along the direction [111] presents the most stable structure. Values of the coefficient of thermal expansion, the Debye temperature, and the Grüneisen parameter show that at low temperatures the specific heat at constant pressure and constant volume has a similar behavior, with a value for the Dulong-Petit limit expected for a triclinic perovskite-type structure. Finally, measures of susceptibility as a function of temperature suggest an antiferromagnetic behavior, with Néel temperature TN = 20.1 K. From the Curie-Weiss adjust, the temperature independent susceptibility was determined to be χo = 0.0038 emu/mol and the effective magnetic moment μ = Peff = μB = 1.30 μB.

Evaluation of the effect of the synthesis method on the performance of manganese spinel as cathode material in lithium-ion batteries

Spinel-structured lithium manganese oxide (LiMn2O4) has been successfully used as a cathode material for various lithium batteries. To improve the capacity and increase the discharge potential of the battery, transition metals are commonly added to the spinel as dopants or as a substitute for manganese. This can also confer stability on the structure of the cathode material. In this work, the production and performance of spinel LiMn2O4 (LMO) and LiN i0.5Mn1.5O4 (LNMO) by solid-state and sol-gel synthesis methods were studied. Synthetized (LMO) and (LNMO) materials were characterized by Raman spectroscopy and X-ray diffraction (XRD) to verify the formation of a spinel-like structure. It was corroborated that both synthesis methods can produce an adequate spinel structure. SEM analyses showed that in general, spinel take an octahedral form. The particle size changes according to the synthesis method used. Lower particle sizes were obtained by sol-gel. The electrochemical characterization demonstrates that solid-state synthesis generates compounds with greater purity and crystallinity, which induces a greater capacity of lithium ion intercalation. The addition of nickel to the spinel increases the discharge potential of the cathode by 0.5V.

Properties and catalytic evaluation of nanometric X zeolites containing linear alkylammonium cations

The reduction of zeolite particle size and the development of methods to enhance the basic properties of catalysts are some of the important research fields currently explored. In light of this, this work aimed at evaluating how the combination of crystallite size reduction and ion exchange of micro- and nanocrystalline NaX zeolites with different chain-length linear alkylammonium cations affects their overall properties, Lewis basicity and catalytic activity. Scanning electron microscopy (SEM) analyses showed that micro- and nanocrystalline NaX possessed octahedral and undefined crystalline forms, respectively, both being polycrystalline. 27Al and 29Si MAS-nuclear magnetic resonance (NMR) analyses revealed that nanocrystalline zeolites presented lower long-range organization, forming a less rigid structure with more accessible sites, which is a desirable feature for catalytic applications. These characteristics were confirmed using a range of techniques: nitrogen physisorption, thermogravimetric analysis and catalytic evaluation. Nanocrystalline zeolites exhibited higher exchange degrees than the microcrystalline zeolites, because the smaller crystal sizes and the higher mesoporosity of the former enhance the accessibility to the exchangeable sites and reduce steric hindrance. Catalytic evaluation of the zeolites via Knoevenagel condensation reaction between butyraldehyde and ethyl cyanoacetate confirmed the advantages of both zeolite modification methods Ion-exchanged zeolites presented higher catalytic activity than NaX zeolites. Zeolites with nanometric crystals showed greater conversions, and higher reaction rates than the micrometric. In addition, most of the nanosized catalysts presented higher turnover frequencies at zero reaction time.

Multidimensional structural variation in the cyanotrichite family of merotypes: camerolaite-3b-F\bar 1.

A new superstructure of the mineral camerolaite, Cu6Al3(OH)18(H2O)2[Sb(OH)6](SO4), has been refined in space group P\bar 1 with unit-cell parameters aP = 7.7660 (16), bP = 8.759 (4), cP = 11.306 (2) Å, αP = 108.67 (4), βP = 83.41 (3), γP = 126.64 (2)°, V = 581.6 (3) Å3 and Z = 1, with R1 = 0.0951 (all data). This is the first refined example of a cyanotrichite-group mineral in which long-range order of interlayer anions produces a superstructure along b, although diffuse scattering has previously been reported that corresponds to short-range order. Though the structure shares with other members of the cyanotrichite group a structural unit in which ribbons of edge-sharing Cu and Al octahedra form layers || (001), the superstructure arises from regular alternation of [SO4] and [Sb(OH)6] polyhedra along rods that lie between the layers, and phase coupling between rods that maximizes the distance between [SO4] groups of adjacent rods along a and c directions. This arrangement suggests an alternative nearly orthogonal choice of unit cell in F\bar 1 with parameters aF = 12.473 (26), bF = 8.759 (4), cF = 21.476 (7) Å, αF = 85.94 (4), βF = 95.91 (5), γF = 92.34 (9)°, which is recommended for comparing this structural variety of camerolaite with other members of the group.

Structure and properties of barium niobophosphate glasses

Phosphate glasses of the ternary system BaO-Nb2O5-P2O5 were studied in two compositional series, namely 40BaO-xNb2O5-(60-x)P2O5 (series A), with x=0–40mol% Nb2O5, and yBaO-20Nb2O5-(80-y)P2O5 (series B), with y=20–60mol% BaO. Nine homogeneous glassy samples were prepared altogether in both series, and their basic physical properties (density, molar volume, glass transition temperature, dilatometric softening temperature and thermal expansion coefficient) were determined. The chemical durability of the Nb2O5-containing glasses is high and the dissolution rate at 80°C is lower than 4–5×10−8gcm−2min−1. The glass transition temperature of the glasses in series A increased significantly with increasing Nb2O5 content from 324 to 727°C, whereas in the series B with increasing BaO content, Tg increased within the range 620–725°C. The index of refraction increased more steeply in glass series A with increasing Nb2O5 content than in the glass series B. According to the Raman spectra in the glass series A, at low Nb2O5 content niobium forms isolated octahedra NbO6 incorporated in the glass network, but when Nb2O5 content increases, these octahedra are linked into chains and further into three-dimensional clusters. In glass series B, NbO6 octahedra form only NbONbO chains connecting NbO6 octahedra. NbO6 octahedra clustering is reflected also in the 31P MAS NMR spectra of BaO-Nb2O5-P2O5 glasses showing on a non-monotonous transformation of phosphate units in the direction Q3→Q2→Q1→Q0, both with increasing Nb2O5 content in the first A series and BaO content in the second B series.

Temperature Dependent Magnetic Susceptibility and Equilibrium Studies in Solution: Evans’s Method

The chemical shift in a solvent caused by the presence of a paramagnetic species and the temperature dependence of the chemical shift difference to determine the temperature dependent magnetic susceptibility can be studied using Evans method. The method is very useful because a common NMR instrument, easily accessible in a department of chemistry, allows the accurate measurement of paramagnetic susceptibilities. The present review highlights planar (S = 0) and octahedral (S = 1) forms of Ni(II) complexes are in equilibrium and has been followed in the temperature range 298 − 338 K by 1H NMR technique using the protocol of Evans’s method.

Structural comparison of copper(II) thiocyanate pyridine complexes

Copper(II) thiocyanate forms a series of closely related complexes when reacted with substituted pyridines (XPy) in methanol. Although these compounds are nominally square planar trans-[Cu(NCS)2(XPy)2], most show N,S-thiocyanate bridging via long Cu–S bonds of ⩾2.7Å. The resulting Jahn-Teller (J-T) distorted octahedra form edge-sharing chains. However, these units can also form sheets or small oligomers. For some 2- or 3-substituted pyridines, isolated square planar trans-[Cu(NCS)2(XPy)2], J-T distorted octahedral trans-[Cu(NCS)2(XPy)2(MeOH)2], or square pyramid trans-[Cu(NCS)2(XPy)2(MeOH)] were isolated. Polymorphism and/or solvento isomers appear to be common, being identified for five of 21 ligands studied. Use of 2-NH2Py produces methoxy-bridged dimers [Cu2(NCS)2(2-NH2Py)2(μ-OMe)2] that are further linked via bridging thiocyanate to form a sheet structure. Unusual aryl bromide metal chelation is noted in the mixed ligand complex trans-[Cu(NCS)2(2-BrPy)(3-BrPy)]. When LL=4,4′-bipyridyl (Bpy) or pyrazine (Pyz) is used, bridging by both the organic and thiocyanate ligands produces sheet networks, trans-[Cu(NCS)2(LL)].

Stable monolayer honeycomb-like structures ofRuX2(X=S,Se)

Recent studies show that several metal oxides and dichalcogenides $(M{X}_{2})$, which exist in nature, can be stable in two-dimensional (2D) form and each year several new $M{X}_{2}$ structures are explored. The unstable structures in $H$ (hexagonal) or $T$ (octahedral) forms can be stabilized through Peierls distortion. In this paper, we propose new 2D forms of ${\mathrm{RuS}}_{2}$ and ${\mathrm{RuSe}}_{2}$ materials. We investigate in detail the stability, electronic, magnetic, optical, and thermodynamic properties of 2D $\mathrm{Ru}{X}_{2}$ $(X=\text{S},\text{Se})$ structures from first principles. While their $H$ and $T$ structures are unstable, the distorted $T$ structures $({T}^{\ensuremath{'}}\text{\ensuremath{-}}\mathrm{Ru}{X}_{2})$ are stable and have a nonmagnetic semiconducting ground state. The molecular dynamic simulations also confirm that ${T}^{\ensuremath{'}}\text{\ensuremath{-}}\mathrm{Ru}{X}_{2}$ systems are stable even at 500 K without any structural deformation. ${T}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{RuS}}_{2}$ and ${T}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{RuSe}}_{2}$ have indirect band gaps with 0.745 eV (1.694 eV with HSE) and 0.798 eV (1.675 eV with HSE) gap values, respectively. We also examine their bilayer and trilayer forms and find direct and smaller band gaps. We find that AA stacking is more favorable than the AB configuration. The new 2D materials obtained can be good candidates with striking properties for applications in semiconductor electronic, optoelectronic devices, and sensor technology.

Structure and spectroscopic properties of (Y, Eu)(PO3)3 polyphosphate red phosphors

A series of orange-red emitting phosphor Y(PO3)3: xEu3+ (x = 0.1–1.0) was prepared by a solid-state reaction route. The phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) as well as decay lifetimes. Studies revealed the phase transfer from monoclinic to orthorhombic when Y3+ is totally replaced by Eu3+, and expansion of the unit cell occurs with increasing Eu3+ doped content. The PL spectra show that the phosphors Y(PO3)3: xEu3+ can be effectively excited by near ultraviolet (n-UV) light, and exhibit strong red-orange emission with no concentration quenching. The profile of PL spectra changes significantly at high Eu3+ content (x ≥ 0.80), which is due to the variation of preference for substitution of Eu3+. The luminescence due to the 5D0 → 7FJ (J = 1, 2) transitions at 77 K exhibits its own spectral features for different crystallographic site. It is found that Eu3+ ions occupy the centers of octahedral polyhedron and form Ci/C1 point group in Y(PO3)3.

Time-resolved luminescence spectroscopy of structurally disordered K3WO3F3 crystals

Three emission centers of exciton-like origin, with distinct relaxation time, emission and excitation spectra were revealed in K3WO3F3 and described taking into account its structural disordering. Low-temperature monoclinic phase of K3WO3F3 features few anion sites with mixed oxygen/fluorine occupancy per [WO3F3] octahedron. Therefore, different kinds of distorted octahedra form, providing different luminescence centers. The time-resolved luminescence spectroscopy technique was applied to distinguish these centers. The simultaneous thermal quenching of them above ∼200 K was qualitatively explained involving dynamic structural disorder of the compound. The energy transfer mechanism between centers was found and tentatively described by the diffusion of excitons. Apart from intrinsic luminescence, the PL of defect-related centers was discovered and the role of shallow charge carrier traps in the low-temperature persistent luminescence was revealed.

Effects of particle shape on the thermoelastoplastic behavior of particle reinforced composites

Particle shape effects in thermoelastoplastic ductile matrix composites are evaluated systematically. This is done by studying generic, periodic, multi-inhomogeneity volume elements that contain 20 volume percent of randomly positioned and, where applicable, randomly oriented, identical particles taking the form of spheres, regular octahedra, cubes, or regular tetrahedra. The Finite Element method is used for obtaining the responses of the initially stress-free volume elements to single, stress controlled loading cycles at four fixed macroscopic stress triaxialities, viz., loading by shear, uniaxial, in-plane hydrostatic, and hydrostatic applied stresses. In addition, a thermal loading cycle and the effects of residual stresses on shear loading are considered. Results are evaluated as ensemble averages over five phase arrangements of each type. They are presented in terms of macroscopic responses as well as the evolution of the phase-level averages and standard deviations of the microscopic stress and strain fields. Consistent shape effects are predicted for all load cases considered, with the responses of cube-shaped and octahedral particles being fairly similar and lying between the predictions obtained for spherical and tetrahedral inhomogeneities. Among the shapes studied, tetrahedral particles are found to give rise to the stiffest responses under mechanical loading.

STUDY OF THE MAGNETITE OXIDATION

To study the process of magnetite oxidation the experiments had been conducted on large single crystals of magnetite having octahedral form and retrieved from chlorite schist in Shabrovski talc mine (the Middle Urals). Using the method of diff erential thermal curves obtained by diff erential heating of samples the good reproducibility of the processes that occur during oxidative roasting magnetite was shown. The mechanism of the magnetite oxidation and temperature ranges of exothermic and endothermic reactions in various stages of magnetite oxidation was considered. Using the method of separated standard the unknown thermal eff ect of magnetite oxidation was determined in accordance with the standard thermal effect (CaCO3 ) and the values obtained in the areas of the fi gures in thermograms concluded between the diff erential heating curve and the axis of time proportional to the thermal eff ects of the standard and the test substances (Fe3O4 ). The obtained results are of some interest. Knowing the temperature intervals of magnetite oxidation, it can be taken into account in establishing the mode of burning heat source for technological zones in conveyor type roasting machines. This achieves optimization of the fi ring thermal regime and reduction in specifi c fuel consumption

Nanostructured coordination complexes/polymers derived from cardanol: “one-pot, two-step” solventless synthesis and characterization

An eco-design of Cardanol and Mn(ii)/Co(ii) based nanostructured CP with octahedral geometry and form micro to nano spheres that self arranged to contour amorphous, layered morphology with desirable antibiofilm activity and high thermal stability.

Research of the characteristics of particles obtained by treating of CuSO4 solution by the contact nonequilibrium plasma

The paper presents the results of a study of the particles obtained from the synthesized cathode dry deposits. It is noted that the amount of the obtained residual particles can vary within wide limits. At the same time there is the predominance of octahedral and cuboktahedral forms of the particles in the dimension characteristic for fine and ultrafine powders. X-ray diffraction analysis showed the prevalence of oxide copper (I) in these forms. The variation of process parameters, especially the reduction of the current density of the process and therefore reduction of the current density at the cathode lead to reducing the size of the resulting particles and improving uniformity of deposits, as evidenced by the results of electron microscopic studies of the synthesized cathode deposits. This allows controlling the process of synthesis of particles by adjusting the process parameters of plasma chemical treatment, which due to its constructive design isn’t cause difficulties and, along with the possibility of using very dilute solutions, is the advantage of this method.

Structure of a new three-dimensional metal-organic framework: Poly[manganese(II)-bis-(µ4-1,4-naphthalenedicarboxylate)-bis-(N,N-dimethylformamide)

A novel metal-organic framework, [Mn2(C12H6O4)2(C3H7NO)2]n has been synthesized solvothermally by assembling ligands 1,4-naphthalenedicarboxylic acid (NDC), N,N-dimethylformamide (DMF) and manganese(II). Both independent Mn(II) ions are six-coordinated in a distorted octahedral environment with oxygen donors. Bis(bridging bidentate) μ4-η1:η1:η2:η1, NDC ligands orient in two directions, [010] and [001], linking the Mn(II) ions to form a square grid in (100) plane. Corner shared Mn(II) octahedral form chains along a direction resulting in a three dimensional network.

Characterization and structural investigation of lead borophosphate glasses modified by tungsten oxide

The effect of WO3 on the properties and structure of PbO–B2O3–P2O5–WO3 quaternary system was studied. Glasses containing up to 60 mol% WO3 were prepared and the variation of several physical properties was determined with respect to chemical composition in a broad compositional range. Chemical durability of WO3-containing glasses is very high and their thermal stability as well. Glass transition temperature increases with increasing WO3 content up to 566 °C. Glass structure was studied by Raman spectroscopy and 31P and 11B MAS NMR spectroscopy. NMR spectroscopy reveals the formation of B–O–W linkages and also the existence of tetrahedral BO4 units and trigonal units BO3 in the glass structure. With increasing WO3 content in the glasses, the number of starting tetrahedral B(OP)3O units decreases and B–O–P bridges are replaced gradually by B–O–W and B–O–B bridges, while the number of BO3 units increases. Raman spectra of the studied glasses possess a doublet of strong vibrational bands in the range at 800–1000 cm−1, assigned to vibrations of W–O− and WO bonds in tungstate structural units. In glasses with a higher WO3 content WO6 octahedra form tungstate clusters interconnected by W–O–W bridges as reflected in the Raman spectra. The formation of strong P–O–W and B–O–W linkages in the studied glasses explains high chemical durability of the glasses and the observed increase in the glass transition temperature.

Syntheses, crystal structures, and electronic properties of Ba8Si2US14 and Ba8SiFeUS14

Black single crystals of the new compounds Ba8Si2US14 and Ba8SiFeUS14 have been obtained by high-temperature solid-state methods at 1223 K. These isostructural compounds crystallize in a new structure type in space group C2h3 – C2/m of the monoclinic system. The salt-like structure comprises isolated US6 octahedra and MS4 tetrahedra separated by Ba cations. The US6 octahedra form pseudo-layers that are separated by two other pseudo-layers formed by isolated MS4 tetrahedra. These compounds do not show any short S–S interactions. Ba8Si2US14 charge balances with 8 Ba2+, 2 Si4+, 1 U4+, and 14 S2−; Ba8SiFeUS14 can be charge balanced with 8 Ba2+, 1 Si4+, 1 Fe3+, 1 U5+, and 14 S2−. DFT calculations using the HSE functional indicate that the compounds are semiconductors. The calculated band gaps are 1.2 eV and 1.8 eV for Ba8Si2US14 and Ba8SiFeUS14, respectively.