Isolation of p-tricyanovinylphenyldicyanomethide ion via a [2+2] cycloaddition of 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules

In the presence of CoCl₂·6H₂O and dppm (bis(diphenylphosphino) methane), the reaction of TCNQ (7,7,8,8-tetracyanoquinodimethane) molecules by [2+2] cycloaddition forms a p-tricyanovinylphenyldicyanomethide ion (PCQ⁻), which has been obtained as one anion unit in one new compound [Co(dppmdo)₃][PCQ⁻]₂·H₂O 1 (dppmdo = bis(diphylphospine oxide) methane). Its structure was determined by X-ray crystallography: 1 crystallizes in with a = 14.174(3) Å, b = 19.553(4) Å, c = 19.776(4) Å, α = 112.72(3)°, β = 95.43(3)°, γ = 110.79(3)°, and Z = 2. It was characterized by IR spectra, UV–Vis spectra, and cyclic voltammogram. Magnetic properties indicate that no magnetic coupling between PCQ⁻ and [Co(dppmdo)₃]²⁺ unit.     

Cobalt–silicon mixed oxide nanocomposites by modified sol–gel method

Cobalt–silicon mixed oxide materials (Co/Si=0.111, 0.250 and 0.428) were synthesised starting from Co(NO₃)₂·6H₂O and Si(OC₂H₅)₄ using a modified sol–gel method. Structural, textural and surface chemical properties were investigated by thermogravimetric/differential thermal analyses (TG/DTA), XRD, UV–vis, FT-IR spectroscopy and N₂ adsorption at −196 °C. The nature of cobalt species and their interactions with the siloxane matrix were strongly depending on both the cobalt loading and the heat treatment. All dried gels were amorphous and contained Co²⁺ ions forming both tetrahedral and octahedral complexes with the siloxane matrix. After treatment at 400 °C, the sample with lowest Co content appeared amorphous and contained only Co²⁺ tetrahedral complexes, while at higher cobalt loading Co₃O₄ was present as the only crystalline phase, besides Co²⁺ ions strongly interacting with siloxane matrix. At 850 °C, in all samples crystalline Co₂SiO₄ was formed and was the only crystallising phase for the nanocomposite with the lowest cobalt content. All materials retained high surface areas also after treatments at 600 °C and exhibited surface Lewis acidity, due to cationic sites. The presence of cobalt affected the textural properties of the siloxane matrix decreasing microporosity and increasing mesoporosity.     

Polarised IR and Raman spectra of non-centrosymmetric Na3Li(SeO4)2.6H2O crystal--a new Raman laser material

Polarised IR and Raman spectra of Na₃Li(SeO₄)₂·6H₂O single crystal have been recorded. Discussion of the results has been based on the factor group approach for the trigonal R3c (C_3v⁶) space group with Z = 2. The obtained results for the spontaneous Raman scattering have been used in the discussion of the stimulated Raman spectra of the material studied—a new Raman laser crystal.     

Reversible photomagnetic properties of the molecular compound [{Cu(bipy)2}2{Mo(CN)8}]·9H2O·CH3OH

The optical and photomagnetic properties of [{Cu^II(bipy)₂}₂{Mo^IV(CN)₈}]·9H₂O·CH₃OH (1) have been reinvestigated. A comparison between spectra in solution and in the solid state revealed the presence of an intervalence band (or Metal–Metal Charge Transfer, hereafter noted MMCT) at 570 nm. The photomagnetic properties have been performed in a Superconducting QUantum Interference Device at 10 K with irradiation in the range of the MMCT: 488 nm, 520 nm and 647 nm at 10 K. An important increase of the magnetic signal has been measured after 1 h of irradiation at 488 nm, whereas a weaker increase has been obtained for the irradiation at 520 nm in the same conditions. Moreover, after an excitation at 488 nm, an irradiation at 647 nm has induced a decrease of the magnetic moment, which corresponds to a partial deexcitation. The complete characterization of the photoproduct has been realised after an irradiation of 4 h at 488 nm. The photomagnetic properties have shown an increase of the paramagnetism of 1 at low temperature. After a thermal heating at 300 K, the material goes back to its initial state before irradiation. It is the first time that a fully reversible photomagnetic behaviour for the compound [{Cu^II(bipy)₂}₂{Mo^IV(CN)₈}]·9H₂O·CH₃OH has been described. The observed properties have been discussed in terms of an electron transfer mechanism Mo → Cu.     

The O–H···O, O–H···N and C–H···O hydrogen bonds in 1,4-dimethylpiperazine mono-betaine monohydrate

1,4-Dimethylpiperazine mono-betaine (1-carboxymethyl-1,4-dimethylpiperazinium inner salt, MBPZ) crystallizes as monohydrate. The crystals are orthorhombic, space group Pccn. Two MBPZ molecules and two water molecules form a cyclic oligomer, (MBPZ·H₂O)₂. The O–H···O and O–H···N hydrogen bonds are of 2.769(1) and 2.902(1) Å, respectively. The dimers interact with the neighboring molecules through the C–H···O hydrogen bonds of 3.234(1) Å. The piperazine ring assumes a chair conformation with the N(4)–CH₃ and N⁺(1)–CH₂COO⁻ groups in the equatorial position and the N⁺(1)–CH₃ group in the axial one. The FTIR spectrum is compared with that calculated by the B3LYP/6-31G(d,p) level of theory.     

Development of mullite and mullite/Al2O3 precursor sols for electrophoretic deposition of oxidation protection coatings

Mullite and mullite/Al₂O₃ precursor sols have been developed for the deposition of oxidation barrier coatings on carbon fibre reinforced composites using a combination of sol–gel synthesis and electrophoresis.The sols were synthesised by controlled hydrolysis and condensation of TEOS (tetraethoxysilane) and Al(OBu^s)₃ (aluminium tri-sec-butylate). The main objective was the definition of synthesis conditions which yield sols suitable for the electrophoretic deposition (EPD). Measurements of the Electrokinetic Sonic Amplitude were used to investigate the electrokinetic properties of the sols in the as-prepared state and depending on the later addition of H₂O. ²⁹Si CP/MAS NMR spectra of dried precursor samples were recorded to study the homogeneity of Al/Si mixture. The progress of crystallisation with increasing temperature of heat treatment was examined by XRD. Oxidation protection coatings on C/C–SiC composites were prepared by EPD.Whereas a low H₂O to TEOS ratio during the sol synthesis was advantageous for a low mullite formation temperature, a high H₂O to TEOS ratio was necessary to enable the EPD. The synthesis of a sol with a low H₂O to TEOS ratio in the first step and the later modification of this sol by the addition of water was a successful method to combine the required electrokinetic properties and mullitisation temperatures below 1200 °C.     

Syntheses and characterizations of five coordination polymers constructed by 3,5-bis(pyridin-3-ylmethoxy)benzoic acid ligand

Five coordination polymers, namely [Cd(L3)₂]·H₂O (1), [Zn(L3)₂] (2), [Co(L3)₂] (3), [Ni(L3)₂] (4) and [Cu₂(L3)₂]·3H₂O (5), where L3 = 3,5-bis(pyridin-3-ylmethoxy)benzoic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. Compound 1 is a binodal (3,4)-connected net with (6³)(6⁶) topology. Compounds 2–4 are isostructural and described by the uninodal (4,4)-connected net with (4⁴ · 6²) Schläfli symbol. The structure of 5 is a 2D binodal (6,3) net. In addition, the luminescent properties of compounds 1 and 2 have been studied in the solid state at room temperature.     

Crystal chemistry of three new monodimensional fluorometalates templated with ethylenediamine

Three new monodimensional hybrid metal (Ti, In, Al) fluorides are synthesized with ethylenediamine (en) as a templating agent in solvothermal conditions assisted by microwave heating. All structures involve inorganic chains built up from TiO₂F₄ octahedra connected by two opposite O²⁻ vertices in [H₂en]·(TiOF₄) (I), from InF₆(H₂O) pentagonal bipyramids linked by F–F edges in [H₂en]·(InF₄(H₂O))₂·H₂O (II) and from (Al₇F₃₀)⁹⁻ polyanions sharing two opposite AlF₆ octahedra in [H₂en]₃·(Al₆F₂₄) (III). I is tetragonal, P4/ncc, a = 12.761(3) Å, c = 8.041(3) Å; II is orthorhombic, F2dd, a = 6.904(5) Å, b = 16.559(5) Å, c = 19.777(4) Å and III is monoclinic, P2₁/n, a = 9.387(2) Å, b = 6.710(2) Å, c = 21.513(6) Å, β = 97.18(3)°.     

Molybdenum(VI) network polymers based on anion–π interaction and hydrogen bonding: Synthesis, crystal structures and oxidation catalytic application

A crystallographic investigation of anion–π interactions and hydrogen bonds on the preferred structural motifs of molybdenum(VI) complexes has been carried out. Two molybdenum(VI) network polymers MoO₂F₄·(Hinca)₂ (1) and MoO₂F₃(H₂O)·(Hinpa) (2), where inca = isonicotinamide and inpa = isonipecotamide, have been synthesized, crystallographically characterized and successfully applied to alcohol oxidation reaction. Complex 1 crystallizes in the monoclinic space C2/c: a = 16.832(3) Å, b = 8.8189(15) Å, c = 12.568(2) Å, β = 118.929(3)°, V = 1560.1(5) Å³, Z = 4. Complex 2 crystallizes in the triclinic space P-1: a = 5.459(2) Å, b = 9.189(4) Å, c = 12.204(5) Å, α = 71.341(6)°, β = 81.712(7)°, γ = 77.705(7)°, V = 564.8(4) Å³, Z = 2. Complex 1 consists of hydrogen bonding and anion–π interactions, both of which are considered as important factors for controlling the geometric features and packing characteristics of the crystal structure. The geometry of the sandwich complex of [MoO₂F₄]²⁻ with two pyridine rings indicates that the anion–π interaction is an additive and provides a base for the design and synthesis of new complexes. For complex 2, the anions and the protonated inpa ligands form a 2D supramolecular network by four different types of hydrogen contacts (N–HF, N–HO, O–HF and O–HO). The catalytic ability of complexes 1 and 2 has also been evaluated by applying them to the oxidation of benzyl alcohol with TBHP as oxidant.     

Formation of Cr(III) Hydroxides from Chrome Alum Solutions: 1. Precipitation of Active Chromium Hydroxide

The formation of active chromium hydroxide, Cr(OH)₃·3H₂O, was studied through potentiometric titrations and turbidimetric measurements. UV-Vis and IR spectroscopies were also employed to characterize the synthesized solid. The rapid addition of NaOH solution to aqueous chrome alum (KCr(SO₄)₂·12H₂O) solutions caused the immediate precipitation of the active material. Only monomeric Cr(III) species seemed to be participating in the precipitation process; neither chromium polymers nor complexes with anions (SO²⁻₄, Cl⁻, NO⁻₃, ClO⁻₄) influenced the fast formation of Cr(OH)₃·3H₂O. Titration studies allowed the determination of several hydrolysis and precipitation constants for Cr(III). Nevertheless, they cannot be used for the estimate of Cr(OH)⁰₃formation constant.     

Photoacoustic spectra of Nd(TFA)3 · 2H2O and Nd(HFA)3 · 2H2O

A new synthesis of trisfluoroacetylactone (TFA) and hexafluoroacetylactone (HFA) Nd complexes: Nd(TFA)₃ · 2H₂O and Hd(HFA)₃ · 2H₂O is reported. The photoacoustic (PA) spectra in the 300–800 nm region of the compounds NdCl₃ · 6H₂O, Nd(TFA)₃ · 2H₂O and Nd(HFA)₃ · 2H₂O are reported. The PA absorption bands are assigned and their relative intensities represented by intensity branching vectors are calculated. The perturbation of the ligand on the energy levels of Nd³⁺ ion is discussed and a model of the relaxation process of Nd(HFA)₃ · 2H₂O is proposed based on its PA and absorption spectra.     

Optical properties of a tetradentate bis(beta-diketonate) europium(III) complex

Eu₂(BPOPB)₃H₂O, an europium complex chelated with bis(β-diketone), was synthesized. Its properties have been investigated by absorption spectrum, emission spectrum and luminescence lifetime measurement. The complex displays strong red luminescence upon irradiation at the ligand band around 355 nm, which indicates that the bis-β-diketonate ligand BPOPB is an efficient sensitizer. The Judd–Ofelt parameters obtained from the emission spectrum of Eu₂(BPOPB)₃H₂O have been used to calculate the total spontaneous emission probabilities (A), the radiative lifetime (τ_rad), the fluorescence branching ratio (β) and the stimulated emission cross-sections (σ). The luminescence lifetimes are determined to be 402 and 169 μs for Eu₂(BPOPB)₃H₂O and Eu(DBM)₃(H₂O)₂, respectively. The relationship between the structures of rare-earth complexes and luminescence lifetimes was analyzed. The radiative properties reveal that Eu₂(BPOPB)₃H₂O is potential to be an efficient luminescent material.     

Synthesis and characterization of copper 4-carboxyphenylphosphonates

Three new copper 4-carboxyphenylphosphonates with formulae Cu(HOOCC₆H₄PO₃)·2H₂O, Cu(HOOCC₆H₄PO₃) and Cu₃(OOCC₆H₄PO₃)₂·3H₂O were prepared and characterized by thermogravimetric analysis, X-ray diffraction analysis, energy-dispersive X-ray microanalysis and infrared spectroscopy. The preparation conditions of Cu(HOOCC₆H₄PO₃)·2H₂O and Cu₃(OOCC₆H₄PO₃)₂·3H₂O differ in the acidity of the reaction mixture, where Cu(HOOCC₆H₄PO₃) was prepared under hydrothermal conditions. Copper 4-carboxyphenylphosphonate with formula Cu₃(OOCC₆H₄PO₃)₂·3H₂O reacts with 4-carboxyphenylphosphonic acid to form Cu(HOOCC₆H₄PO₃)·2H₂O.Cu(HOOCC₆H₄PO₃)·2H₂O is orthorhombic, space group Pbcn (no. 60), a=8.234(2) Å, b=9.438(2) Å, c=24.899(5) Å. Cu(HOOCC₆H₄PO₃) crystallizes in the monoclinic space group P2₁/c (no. 14), a=19.0951(3), b=8.0968(4), c=5.2111(11) Å, β=94.914(6)°, Z=4. Its layered structure is composed of distorted CuO₆ octahedra arranged hexagonally in a gibbsite-like manner around two phosphonate groups, which have their carboxyphenyl groups extending into the space above and below the copper–phosphonate layer. Infrared spectra indicate that for both Cu(HOOCC₆H₄PO₃)·2H₂O and Cu(HOOCC₆H₄PO₃) the acid hydrogen is present at the carboxyl group and not at the phosphonic group.     

Glass–ceramic Li2S–P2S5 electrolytes prepared by a single step ball billing process and their application for all-solid-state lithium–ion batteries

We report that glass–ceramic Li₂S–P₂S₅ electrolytes can be prepared by a single step ball milling (SSBM) process. Mechanical ball milling of the xLi₂S·(100 − x)P₂S₅ system at 55 °C produced crystalline glass–ceramic materials exhibiting high Li-ion conductivity over 10⁻³ S cm⁻¹ at room temperature with a wide electrochemical stability window of 5 V. Silicon nanoparticles were evaluated as anode material in a solid-state Li battery employing the glass–ceramic electrolyte produced by the SSBM process and showed outstanding cycling stability.     

Optical spectroscopy of europium 3,5-dinitrosalicylates—Intense red luminophores

It was found, that alkali metal-europium dinitrosalicylates of composition M₃Eu(3,5-NO₂-Sal)₃·nH₂O (M = Li, Na, K, Cs) are intense red luminophores with wide excitation band. Using methods of optical spectroscopy we studied the influence of nitrogroups and alkali metal counterions on Eu³⁺ luminescence efficiency and on processes of excitation energy transfer to Eu³⁺ ion in compounds synthesized. The Eu³⁺ luminescence and Eu³⁺ luminescence excitation spectra, as well as vibrational IR and Raman spectra were investigated. Details of the structure of compounds were discussed. The network of hydrogen bonds in lanthanide dinitrosalicylates is weakening at introduction of large alkali metal ions in compounds and at the increase of the temperature. As a consequence, the long-wavelength shift of the intraligand charge transfer (ILCT) band in Eu³⁺ excitation spectra arises at inclusion of Cs⁺ cations instead of Li⁺ in the crystal lattice of europium dinitrosalicylates and at heating of these compounds. To obtain the energy of the lowest excited triplet state the phosphorescence spectra of alkali metal-gadolinium compounds M₃Gd(3,5-NO₂-Sal)₃·nH₂O, of alkali metal dinitrosalicylate and salicylate salts were measured with time delay. Change of the energies of ligand electronic states and ligand–metal charge transfer state (LM CTS) can give a two-three orders of magnitude enhancement of the Eu³⁺ luminescence efficiency in dinitrosalicylates in comparison with salicylates and ten-fold enhancement at the substitution of Li⁺ and Na⁺ for Cs⁺ in dinitrosalicylates.     

Structural, optical and thermal studies of Eu ions in lithium fluoroborate glasses

Borate glasses doped with trivalent europium were prepared by the conventional melt quenching technique, in the chemical composition of (49.99-x)B₂O₃ + 25Li₂O + 25LiF+xEu₂O₃ by varying the concentration of the rare earth ion in the order 0.01, 0.1, 1, 2 and 3 wt% and their structural, luminescence and thermal behavior have been reported. The XRD and FTIR spectra reveal the glass structure and the functional groups. The UV–VIS, luminescence spectra and lifetime of the Eu³⁺ ions were measured. The local site symmetry around the Eu³⁺ ions were evaluated through the luminescence intensity ratio (R) of the ⁵D₀ → ⁷F₂ to ⁵D₀ → ⁷F₁ transitions. Optical measurements have been carried out to explore the optical properties such as bonding parameters, Judd–Ofelt parameters, stimulated emission cross-section, transition probability, branching ratio, radiative lifetime, etc. The lifetime measurements of the ⁵D₀ level as a function of the concentration of Eu³⁺ ion have been found and is comparable to other reported for Eu³⁺ doped borate, phosphate glasses and higher than that for the tellurite glasses. The thermal properties such as glass transition, crystallization and melting temperatures of the Eu³⁺ glasses were studied through the DSC traces in the temperature range of 30−1200 °C at a heating rate of 10 °C per minute. The change in optical properties with the variation of Eu³⁺ ion concentration have been discussed and compared with similar results.     

Hydrothermal syntheses, crystal structures of three new organic–inorganic hybrids constructed from Keggin-type [BW12O40] clusters and transition metal complexes

Three new organic–inorganic hybrid compounds constructed from Keggin-type polyanions and transition metal complexes, [Mn(2,2′-bipy)₃]_1.5[BW₁₂O₄₀Mn(2,2′-bipy)₂(H₂O)]·0.25H₂O (1), [Fe(2,2′-bipy)₃]_1.5[BW₁₂O₄₀Fe(2,2′-bipy)₂(H₂O)]·0.5H₂O (2) and [Cu₂(phen)₂(OH)₂]₂H[Cu(H₂O)₂{BW₁₂O₄₀Cu_0.75(phen)(H₂O)}₂]·1.5H₂O (3), have been hydrothermally synthesized and characterized by elemental analyses, IR, TGA and single-crystal X-ray diffraction. Compounds 1 and 2 are isostructural and both exhibit monosupporting polyoxometalate cluster structure, each of which contains a [BW₁₂O₄₀]⁵⁻ cluster decorated by one transition metal complex. Compound 3 contains a bisupporting polyoxometalate cluster anion where two {Cu_0.75(phen)(H₂O)}^0.75+ fragments are supported on the polyoxometalate dimer {Cu(H₂O)₂(BW₁₂O₄₀)₂}⁸⁻, this represents the first bisupporting polyoxometalate cluster based on a Keggin-type polyoxometalate dimer, which are further packed together via π–π stacking contacts into an extended 1-D chain.     

A novel 18-metallacrown-6 complex: Synthesis, structural characterization and magnetic properties

The novel 18-metallacrown-6 complex, with the formula of [Mn₆(C₁₁H₁₁N₂O₃)₆(CH₃CH₂OH)₆]·3C₃H₇NO·2CH₃CH₂OH (1) (pmshz = N-propanoyl-3-methyl-salicylhydrazide), has been prepared and characterized. The self-assembled, manganese complex assumes a nearly planar cyclic structure with an [Mn–N–N]₆ backbone. Due to the coordination, the ligand enforces the stereochemistry of the Mn³⁺ ions as a propeller shape with alternating …ΔΛΔΛ… configurations. The magnetic properties of the metallacrown molecule are characterized by a weak antiferromagnetic exchange interaction between the Mn³⁺ ion spins with S = 2 in the cyclic system.     

Système ternaire : H2O–Fe(NO3)3–Co(NO3)2 isotherme : 30 °C

Ternary system: H₂O–Fe(NO₃)₃–Co(NO₃)₂ isotherm: 30 °C. The H₂O–Co(NO₃)₂ binary system has been investigated in the –28 to 50 °C temperature range. The solid–liquid equilibria of the ternary system H₂O–Fe(NO₃)₃–Co(NO₃)₂ were studied by using a synthetic method based on conductivity measurements. One isotherm is established at 30 °C, and the stable solid phases that appear are iron nitrate nonahydrate: Fe(NO₃)₃·9 H₂O, iron nitrate hexahydrate: Fe(NO₃)₃·6 H₂O, cobalt nitrate hexahydrate: Co(NO₃)₂·6 H₂O, and cobalt nitrate trihydrate: Co(NO₃)₂·3 H₂O. To cite this article: B. El Goundali et M. Kaddami, C. R. Chimie 9 (2006).     

Dynamical Spin Chirality and Magnetoelectric Effect of α-Glycine

Dynamical spin chirality of α-glycine crystal at 301−302 K was investigated by DC (direct current)-magnetic susceptibility measurement at temperatures ranging from 2 to 315 K under the external magnetic fields (H=±1 T) parallel to the b axis. The α-glycine crystallizes in space group P2₁/n with four molecules in a cell, which has centrosymmetric charge distribution. The bifurcated hydrogen bonds N⁺(3)−H(8)···O(1) and N⁺(3)−H(8)···O(2) are stacked along the b axis with different bond intensities and angles, which form anti-parallel double layers. Atomic force spectroscopy result at 303 K indicated that the surface molecular structures of α-glycine formed a regular flexuous framework in the b axis direction. The strong temperature dependence is related to the reorientation of NH³⁺ group and the electron spin flip-flop of (N⁺H) mode. Under the opposite external magnetic field of 1 T and −1 T, the electron spins of N⁺(3)−H(8)···O(1) and N⁺(3)−H(8)···O(2) flip-flop at 301−302 K. These results suggested a mechanism of the magnetoelectric effect based on the dynamical spin chirality of (N⁺H), which induced the electric polarization to produce the onset of pyroelectricity of α-glycine around 304 K.