Novel Three-Dimensional Copper(II) 1,2- Ethylenediphosphonate Framework with Channel-like Voids

Turquoise monoclinic single crystals of the novel three-dimensional Cu2[μ8- O3P(CH2)2PO3)]*3.2H2O coordination polymer have been prepared using the silica gel method. Space group C2/m (no. 12) with a = 1483.6(2), b = 668.44(8), c = 436.30(6) pm, beta = 93.28(2)°. The Cu2+ cation is coordinated by four oxygen atoms stemming from the 1,2- ethylenediphosphonate dianions in a square planar manner and two water molecules in the axial positions. The connection between the Cu2+ cations and the [PO3C] units from the 1,2- ethylenediphosphonate dianions leads to layers parallel to (100), which are linked by the ethylene groups to a three-dimensional framework with channel-like voids. The voids accommodate water molecules not bound to Cu2+ and extend parallel along [001] with an opening of about 550 x 260 pm. Magnetic measurements reveal an antiferromagnetic behaviour due to a superexchange coupling between Cu2+ ions through an oxygen bridge. The UV-Vis spectrum reveals three d-d transition bands at 694, 774, and 918 nm. The compound can be fully dehydrated by thermal treatment and rehydrated by storage in ambient air

Barium titanate via thermal decomposition of Ba,Tiprecursor complexes: The nature of the intermediate phases

The thermal decomposition of Ba,Ti-precursor complexes, containing organic ligands and suitable for the single-source preparation of nanocrystalline BaTiO3, leads firstly to the segregation of specific Ba-rich and Ti-rich phases. Quantitative electron energy loss spectroscopy and powder X-ray diffraction data indicated that the (i) Ba-rich phase is a BaOstabilised variant of the calcite-type high-temperature modification of BaCO3 and (ii) Ti-rich phases are represented by low crystalline barium titanates with the general Ba:Ti ratio close to 1:4. The subsequent solid state reaction between these phases results then in the formation of BaTiO3

Synthesis, phase evolution and properties of phase-pure nanocrystalline BiFeO3 prepared by a starch-based combustion method

The preparation of phase-pure nano-sized BiFeO3 by a combustion-like method using starch as complexing agent is described herein. Phase evolution and development of the crystallite size during the synthesis were monitored depending on the heat treatment and the composition of the (BiFe)-gels. Phase-pure BiFeO3 was obtained at a low heating rate and calcination temperatures between 500 and 600 °C. Above 600 °C the BiFeO3 gradually decomposed to Bi25FeO40 and Bi2Fe4O9. The investigations showed that the appearance of secondary phases depends on the heating rate, calcination temperature, and the fuel to oxidizer ratio in the (BiFe)-gel. The use of HNO3 instead of acetic acid in the preparation of the (BiFe)-gel promotes the formation of secondary phases. To study the phase stability the phase-pure BiFeO3 powder (1c) obtained after calcining at 550 °C (dcryst = 37 nm) was sintered to ceramic bodies up to 800 °C. During sintering the BiFeO3 phase decomposed to Bi25FeO40 and Bi2Fe4O9 gradually. The activation energy for the decomposition process during sintering was calculated to 337±19 kJ/mol using the Johnson–Mehl–Avrami– Kolmogorov (JMAK) model. Magnetic measurements on phase-pure BiFeO3 powders show maximal magnetization of about 0.7 emu/g at 90 kOe and coercivities between 5−7 kOe at 300 K. Investigations at 10 K reveal a loop shift (exchange-bias) up to 2.9 kOe in the negative direction. The optical band gaps of the phase-pure BiFeO3 powders were determined as 2.28(4) eV

Investigations of BaFe0.5Nb0.5O3 nano powders prepared by a low temperature aqueous synthesis and resulting ceramics

A facile method to prepare nanoscaled BaFe0.5Nb0.5O3 via synthesis in boiling NaOH solution is described herein. The nano-crystalline powder has a high specific surface area of 55 m2 g−1 and a crystallite size of 15 nm. The as-prepared powder does not show any significant crystallite growth up to 700 °C. The activation energy of the crystallite growth process was calculated as 590 kJ mol−1. Dense ceramics can be obtained either after sintering at 1200 °C for 1 h or after two-step sintering at 1000 °C for 10 h. The average grain sizes of ceramic bodies can be tuned between 0.23 μm and 12 μm. The thermal expansion coefficient was determined as 11.4(3)⋅10−6 K−1. The optical band gap varies between 2.90(5) and 2.63(3) eV. Magnetic measurements gave a Néel temperature of 20 K. Depending on the sintering regime, the ceramic samples reach permittivity values between 2800 and 137000 at RT and 1 kHz

Strukturelle Untersuchungen an polymeren Koordinationsverbindungen mit Anionen von Benzolcarbonsäuren und der Quadratsäure

Polymere Koordinationsverbindungen erwecken gegenwärtig großes Interesse. Zum Aufbau eignen sich Anionen von Benzolcarbonsäure sowie das Quadratatdianion. Mit geeigneten Metallkationen lassen sich ein-, zwei- und dreidimensionale unendliche Verbände aufbauen. Unter Verwendung von Templatmolekülen eröffnet sich der Zugang zu zeolithartigen Strukturen. Dabei ist es notwendig strukturbestimmende Faktoren zu erkennen. Der Aufbau der Verbindungen wurde u.a. mit Hilfe von Einkristallstrukturanalysen aufgeklärt

Syntheses and Crystal Structures of Two Cadmium Methanetetrabenzoates Featured by Open Framework and Infinite Layers

International audienceColourless single crystals of Cd2[μ8-MTB]*3H2O*DMF (1) were prepared in DMF/H2O solution. 1: Space group C2/c (no. 15) with a = 1821.30(6), b = 2175.08(6), c = 1269.87(4) pm, β = 129.684(1)°. The connection between the methane-p-benzoate tetraanions (MTB4−) and the Cd2+ cations leads to a three-dimensional framework with channels extending along [ 10] and [110] with openings of 670 pm × 360 pm. The channel-like voids accommodate water molecules and N,N-dimethylformamide (DMF) molecules not bound to Cd2+. Colourless single crystals of [Cd4(2,2′-bipy)4(μ7-MTB)2]*7DMF (2) were prepared in DMF in the presence of 2,2'-bipyridine. 2: Space group P (no. 2) with a = 1224.84(4), b = 1418.85(5), c = 2033.49(4) pm, α = 85.831(2)°, β = 88.351(2)°, γ = 68.261(1)°. The coordination of MTB4− to Cd2+ results in infinite layers parallel to (001). The layers, not connected by any hydrogen bonds, contain small openings of about 320 pm × 340 pm

Fine-grained magnetoelectric Sr0.5Ba0.5Nb2O6–CoFe2O4 composites synthesized by a straightforward one-pot method

Magnetoelectric (Sr0.5Ba0.5Nb2O6)1x(CoFe2O4)x (x = 0.2–0.6) composites were prepared by a one-pot softchemistry synthesis using PEG400. Calcining at 700 ◦C resulted in nanocrystalline composite powders (dcryst. = 24–30 nm) which were sintered between 1050 and 1200 ◦C to ceramic bodies with relative densities up to 98%. SEM investigations confirm the formation of composite ceramics with a 0–3 connectivity and variable grain sizes from 0.2 to 3.6 μm for sintering up to 1150 ◦C, while sintering at 1200 ◦C leads both to a change in the microstructure and a considerable grain growth. Magnetic measurements at 300 K reveal ferrimagnetic behaviour with saturation magnetization values smaller than bulk CoFe2O4 and coercivities between 790 and 160 Oe. Temperature-dependent impedance spectroscopy showed that the relative permittivities decrease both with rising frequency and CoFe2O4 fraction. The frequency dependence of the impedance can be well described using a single RC circuit. Magnetoelectric measurements show the presence of pronounced field hystereses. The maximum magnetoelectric coefficient (αME) depends both on the CoFe2O4 fraction (x) and sintering temperature. The composite with x = 0.3 exhibits the largest αME value of 37 μV Oe1 cm1 (@ 900 Hz). With rising frequency of the AC driving field αME increases up to 300–400 Hz and is nearly constant until 1 kHz

Mixed crystalline precursor complexes of the type [Ba(C2H6O2)4][Ti1−xSnx(C2H4O2)3] (x = 0–1) for BaTi1−xSnxO3 ceramics: Synthesis, structure and calcination

The synthesis of [Ba(C2H6O2)4][Ti(C2H4O2)3], its crystal structure and thermal decomposition is described. This 1,2-ethanediolato complex forms with the isotypic tin compound [Ba(C2H6O2)4][Sn(C2H4O2)3] solid solutions [Ba(C2H6O2)4][Ti1−xSnx(C2H4O2)3] in any ratio. Corresponding mixed crystalline samples are suitable precursor complexes for BaTi1−xSnxO3 ceramics with the feature of a heavy element distribution in molecular scale matching the element distribution of the final ceramics

Thermoanalytical, optical, and magnetic investigations on nanocrystalline Li0.5Fe2.5O4 and resulting ceramics prepared by a starch-based softchemistry synthesis

Nanocrystalline Li0.5Fe2.5O4 was prepared by a starch-based soft-chemistry synthesis. Calcining of the (LiFe)-gel between 350 and 1000 °C results in Li0.5Fe2.5O4 powders with crystallite sizes from 13 to 141 nm and specific surface areas between 35 and 7.1 m2 g−1. XRD investigations reveal the formation of ordered Li0.5Fe2.5O4. Sintering between 1050 and 1250 °C leads to ceramics with relative densities of 67−95 % consisting of grains between 0.3 and 54 μm. As the sintering temperature increases a rising weight loss of the ceramic samples was observed due to the loss of Li2O. Temperature-dependent magnetic measurements indicate a superparamagnetic behaviour for the nano-sized samples. Field-dependent measurements at 3 K of ceramics sintered between 1050 and 1200 °C show increasing saturation magnetization values (Ms) of 70.0 to 73.0 emu g−1 most likely due to the formation of lithium vacancies and a decrease of the inversion parameter. The magnetization drops down to 67.7 emu g−1 after sintering at 1250 °C caused by the formation of hematite. Diffuse reflectance spectra reveal an indirect allowed band gap decreasing from 1.93 to 1.60 eV depending on thermal treatment. DSC measurements of the order - disorder phase transition on nano-sized powders and bulk ceramics exhibit transition temperatures between 734 and 755 °C and enthalpy changes (ΔtrsH) ranging from 5.0 to 13.5 J g−1. The linear starch was found to be 11.4⋅10−6 K−1

Preparation and characterization of Ce-MOF/g-C3N4 composites and evaluation of their photocatalytic performance

In this study, unique hybrid structures were constructed between a Ce-based metal-organic framework (Ce-MOF) and graphitic carbon nitride (g-C3N4) materials. In addition, the g-C3N4 materials used for these heterostructures were prepared by five different methods, namely the conventional pyrolysis method, chemical exfoliation by a strong acid, activation by an alkaline hydrothermal treatment, melamine-cyanuric acid supramolecular assembly with a mechanochemical method, and by the solvothermally pre-treated method. The structural and morphological properties of the resulting g-C3N4 sheets and their composites were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis-derivative thermogravimetry (TGA-DTG), diffuse reflectance UV–vis spectroscopy (UV–vis DRS) and N2 sorption-desorption isotherms (BET). Finally, the photocatalytic performance of the composites was determined by following the photocatalytic degradation of methylene blue (MB) in an aqueous solution under UV–visible light irradiation. It was found that the photocatalytic efficiency of the Ce-MOF/g-C3N4‒TS composite was significantly higher than that of their counterparts (Ce-MOF or g-C3N4‒TS) for the photocatalytic degradation of MB. When employing the composite, UV light-induced degradation of MB yielded an efficiency of 96.5% after 120 min for a dye solution containing 10 mg/L MB. This corresponds to a 5-fold or 2-fold improvement of the rate constant (k) when compared to the Ce-MOF or g-C3N4, respectively