The Fe2+ chelate of hydrazinecarboxylic acid studied by the Mössbauer effect

The chelate compounds K[Fe(hyc)₃] and N₂H₅[Fe(hyc)₃]·H₂O (hyc = N₂H₃COO) were studied by the Mössbauer effect of ⁵⁷Fe at various temperatures. At room temperature the quadrupole splitting parameter is 2.77 mm/sec for K[Fe(hyc)₃] and 2.35 mm/sec for N₂H₅[Fe(hyc)₃]·H₂O, and the center shift is 1.08 mm/sec for both compounds. The temperature dependences of the quadrupole parameters yielded the crystal field splittings of the ⁵T_2g levels of the Fe²⁺ ions which indicate large trigonal distortion of the Fe(hyc)₃ anion. Using a molecular crystal-like treatment of the ferrous ion vibrations the temperature dependence of the recoilless fraction gave an effective Debye temperature Θ_D = 71°K for K[Fe(hyc)₃] and Θ_D = 90°K for N₂H₅[Fe(hyc)₃]·H₂O. No evidence for magnetic ordering was found down to 4.5°K in either compound.     

Neutron diffraction study of Li4Ti5O12 at low temperatures

The crystal structure of the “zero-strain” positive electrode material Li₄Ti₅O₁₂ was characterized by neutron powder diffraction in the temperature range 3.4 K–300 K. No phase transition was detected, and the thermal evolution of lattice parameters has been evaluated by the 2nd order Grüneisen approximation using the Debye formalism for internal energy and intrinsic anharmonicity contributions. A relatively high Debye temperature θ_D = 689 ± 71 K was determined. The thermal behavior of cation-anion bond lengths in octahedral and tetrahedral environments is discussed. The lithium diffusion pathway in Li₄Ti₅O₁₂ was discussed on the basis of bond-valence modeling.     

Disordered structures,vibrational spectroscopy,thermal behavior,and electrical properties of two new tetrachlorometallates complexes [(CH3CH2CH2)4N]2MIICl4 with MII = Co and Mn

The two new hybrids single crystals having the general formula [(CH₃CH₂CH₂)₄N]₂M^IICl₄ with M^II = Co (1) and Mn (2) have been synthetised by the slow evaporation process in aqueous solutions. In this article, these compounds were described by the following characterization techniques: X-rays diffraction, thermal analysis (TGA-TDA), vibrational spectroscopy, nuclear magnetic resonance (NMR), and electrical properties. From the crystallographic study, the crystals (1) and (2) have been disclosed to be crystallized too in the centrosymmetric monoclinic systems, with space group P2₁/c (Z = 4) and C2/c (Z = 8), respectively. Their crystal structures consist of [MCl₄]²⁻ anions and two different cations [(CH₃CH₂CH₂)₄N]⁺, which are connected by a three dimensional network of C-H···Cl hydrogen bonds. In both crystals, each M^II center atom being surrounded by four chloride ligands forming a slightly distorted tetrahedral geometry. The tetrahedral [CoCl₄]²⁻ is ordered, while the tetrahedral [MnCl₄]²⁻ is disordered. Some tetrapropylammonium cations of these compounds are found to be disordered. The thermal analysis studies made in the temperature range (298–473 K) did not show any phase transition for the two crystals. Furthermore, the electrical properties of the two compounds are studied by using the complex impedance spectroscopy technique in the temperature and frequency field varied of 290–363 K and 1 kHz–13 MHz, respectively.     

Low temperature structural phase transition of Ba3NaIr2O9

Single crystal X-ray and synchrotron X-ray powder diffraction have been used to probe the structure of Ba₃NaIr₂O₉ from 300 K down to 20 K. Ba₃NaIr₂O₉ is found to undergo a structural transition from hexagonal symmetry, P6₃/mmc, at ambient temperature to monoclinic symmetry, C2/c, at low temperature. The evolution of the unit cell volume upon cooling is indicative of a higher order structural transition, and the symmetry breaking becomes apparent as the temperature is decreased. The low temperature monoclinic structure of Ba₃NaIr₂O₉ contains strongly distorted [NaO₆] and [IrO₆] octahedra in comparison to the room temperature hexagonal structure.     

Superb thermal stability purple-blue phosphor through synergistic effect of emission compensation and nonradiative transition restriction of Eu2+

Phosphors with outstanding luminescence thermal stability are desirable for high-power phosphor-converted light-emitting diode (pc-LED) lightings. High structural rigidity and large bandgap of phosphor hosts are helpful to suppress nonradiative relaxation of optical centers and realize excellent thermal stability. Unfortunately, few host materials simultaneously possess aforementioned structural features. Herein, we confirm that Sr₃(PO₄)₂ (SPO) phosphate possesses high structural rigidity (Debye temperature, Θ_D = 559 K) and large bandgap (E_g = 8.313 eV) by density functional theory calculations. As expected, Eu²⁺-doped SPO purple-blue phosphors show extraordinary thermal stability. At 150/300 °C, SPO:5%Eu²⁺ presents emission loss of only 4%/8% and a predicated ultrahigh thermal quenching temperature of 973 °C. The most strikingly discoveries here are that thermal-induced emission compensation appears within two distinct Eu²⁺ sites of SPO host. The outstanding thermal stability, on one hand, is attributed to rigid structure and large bandgap of host that inhibits nonradiative relaxation of Eu²⁺ and on the other hand, the emission self-compensation of Eu²⁺. Benefiting from synergistic effect of emission compensation and nonradiative transition restriction of Eu²⁺, as-prepared SPO:5%Eu²⁺ purple-blue phosphor not only presents superior thermal stability but also high internal quantum efficiency of 95.1% and excellent hydrolysis resistant. Some advanced applications are explored including white LED lighting and wide-color-gamut display. Our work provides in-deep insights into structure-property relationships of thermally stable phosphors.     

Structural, electronic properties and inter-atomic bonding in layered chalcogenide oxides LaMChO (where M = Cu, Ag, and Ch = S, Se) from FLAPW-GGA calculations

Using the first principles FLAPW-GGA method, comparative study of structural, electronic properties and of chemical bonding in four 1111-like chalcogenide oxides LaMChO (LaCuSO, LaCuSeO, LaAgSO, and LaAgSeO) with ZrCuSiAs-type structure was performed. Our studies showed that: (i) replacements of d metal atoms (Cu ↔ Ag) and chalcogen atoms (S ↔ Se) lead to anisotropic deformations of the crystal structure; this effect is related to strong anisotropy of inter-atomic bonds; (ii) all of the examined chalcogenide oxides are semiconducting; the band gap decreases both at S → Se and Cu → Ag substitutions; and (iii) the bonding in LaMChO phases can be classified as a high-anisotropic mixture of ionic and covalent contributions, where mixed covalent-ionic bonds take place inside [La₂O₂] and [M₂Ch₂] blocks, whereas between the adjacent [La₂O₂]/[M₂Ch₂] blocks, ionic bonds emerge owing to [La₂O₂] → [M₂Ch₂] charge transfer. Since the near-Fermi bands of LaMChO phases originate mainly from electronic states of [M₂Ch₂] blocks, we speculate that chemical substitutions inside these blocks can result in striking differences in electronic properties of these systems; therefore, this approach can be promising for significant enlargement of the functional properties of these materials.     

Photoluminescence properties and application of yellow Ca0.65Si10Al2O0.7N15.3:xEu2+ phosphors for white LEDs

A series of yellow-emitting oxynitride Ca_0.65Si₁₀Al₂O_0.7N_15.3:xEu²⁺ phosphors with α-sialon structure were synthesized. The phase composition and crystal structure were identified by X-ray diffraction and the Rietveld refinement. The excitation and emission spectra, reflectance spectra and thermal stability were investigated in detail, respectively. Results show that Ca_0.65Si₁₀Al₂O_0.7N_15.3:0.12Eu²⁺ phosphors can be efficiently excited by UV-Vis light in the broad range of 290–450 nm and exhibit broad emission spectra peaking at 550–575 nm. The concentration quenching mechanism are discussed in detail and determined to be the dipole-dipole interaction. When the temperature increased to 150 °C, the emission intensity of Ca_0.65Si₁₀Al₂O_0.7N_15.3:0.12Eu²⁺ phosphor is 88.46% of the initial value at room temperature. White LED was fabricated with N-UV LED chip combined with blue Ca₃Si₂O₄N₂:Ce³⁺ and yellow Ca_0.65Si₁₀Al₂O_0.7N_15.3:Eu²⁺ phosphors. The color rendering index and correlated color temperature of this white LED were measured to 78.94 and 6728.12 K, respectively. All above results demonstrate that the as-prepared Ca_0.65Si₁₀Al₂O_0.7N_15.3:xEu²⁺ may serve as a potential yellow phosphor for N-UV w-LEDs.     

Dilatation thermique anormale et caractere en couches des metavanadates MV2O6 (M = Ca,Cd, Zn,Mg, Pb)

The variations of cell parameters and thermal expansion tensors of metavanadates MV₂O₆ have been measured in the range 77–295 K. The thermal expansion anisotropy is characteristic of layer structures especially for brannerite-type structures (M = Cd, Zn, Mg); this anisotropy is explained by the presence of [VO₅] polyhedra, such as occur in the V₂O₅ layer structure. For CaV₂O₆ the variation of thermal expansion as a function of temperature is abnormal: peaks, typical of a diffuse transition, are observed at 260 K for α₁(T) and α₃(T) curves. The temperature anomaly is reduced when cadmium is substituted for calcium.     

Thermal properties of the pyrochlore, Y2Ti2O7

The thermal conductivity and heat capacity of high-purity single crystals of yttrium titanate, Y₂Ti₂O_7, have been determined over the temperature range 2 K?T?300 K. The experimental heat capacity is in very good agreement with an analysis based on three acoustic modes per unit cell (with the Debye characteristic temperature, θ_D, of ca. 970 K) and an assignment of the remaining 63 optic modes, as well as a correction for C_p−C_v. From the integrated heat capacity data, the enthalpy and entropy relative to absolute zero, are, respectively, H(T=298.15 K)−H₀=34.69 kJ mol⁻¹ and S(T=298.15 K)−S₀=211.2 J K⁻¹ mol⁻¹. The thermal conductivity shows a peak at ca. θ_D/50, characteristic of a highly purified crystal in which the phonon mean free path is about 10 μm in the defect/boundary low-temperature limit. The room-temperature thermal conductivity of Y₂Ti₂O₇ is 2.8 W m⁻¹ K⁻¹, close to the calculated theoretical thermal conductivity, κ_min, for fully coupled phonons at high temperatures.     

Dynamics of [Zn(D2O)6] in [Zn(D2O)6][SiF6] crystal as studied by 1D, 2D spectra and spin-lattice relaxation time of H NMR

The dynamics of [Zn(D₂O)₆]²⁺ in [Zn(D₂O)₆][SiF₆] was investigated by ²H NMR one-dimensional spectra, two-dimensional exchange spectra and spin-lattice relaxation time (T₁). The lineshapes of those spectra and T₁ were dominated by the 180° flip of the water molecules and the reorientation of [Zn(D₂O)₆]²⁺ about the C₃ axis. The variation of lineshape of the one-dimensional spectrum below room temperature can be explained by only the 180° flip of the water molecules. The spectrum at room temperature showed a typical shape due to the rapid 180° flip of water molecules. The change in lineshape of the one-dimensional ²H NMR spectrum is caused by the three-site jump of [Zn(D₂O)₆]²⁺ about its C₃ axis above 333 K. Information of the reorientation of [Zn(D₂O)₆]²⁺ below 333 K could not be obtained from the one-dimensional spectrum and T₁. In this temperature range, the two-dimensional exchange spectrum was effective for analysis of molecular motion. The effects of multiple motions, the 180° flip of the water molecules and the reorientation of [Zn(D₂O)₆]²⁺ about the C₃ axis, on the lineshape of the two-dimensional exchange spectrum were studied using spectral simulation.     

Synthesis,crystal structure and magnetic properties of a new tri‐nuclear iron (II,III) complex,a precursor for the preparation of superparamagnetic Fe3O4 nanoparticles applicable in the removal of Cd2+

This study reports the structural and spectroscopic characterization of a novel metal organic compound formulated as [Fe (bpy)₃] [Fe (dipic)₂]₂.7H₂O ( 1 ) (dipic = pyridine‐2,6‐dicarboxylate and bpy = 2,2^′‐bipyridine). 1 was investigated by elemental analysis, FT‐IR spectroscopy, powder X‐ray diffraction and single crystal X‐ray diffraction (SC‐XRD), which revealed a triclinic structure of expected composition. Thermal degradation of 1 was also investigated. Complex 1 was used as a precursor to prepare superparamagnetic nanoparticles of Fe₃O₄ by thermal analysis. The obtained Fe₃O₄ was characterized by Fourier transformed infrared spectroscopy (FT‐IR), powder X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Fe₃O₄ nanoparticles were used as a nano‐adsorbent to remove Cd²⁺ from water at room temperature. The results showed that this nano‐adsorbent is effective in removing Cd²⁺ from contaminated water sources, and that the maximal effectivity of adsorption occurs at pH = 6. Magnetic measurements of complex 1 and Fe₃O₄ nanoparticles at room temperature revealed paramagnetic and superparamagnetic behavior, respectively.     

Synthesis,structure and magnetic properties of iron (II), cobalt (II) and nickel (II) complexes of 2,6-bis(pyrazol-3-yl)pyridine and paramagnetic counterions

Iron (II), cobalt (II) and nickel (II) complexes of 2,6-bis(pyrazol-3-yl)pyridine (bpp) with [Cr(C₂O₄)₃]³⁻ have been prepared. They were characterised by single-crystal X-ray diffraction, magnetic susceptibility measurements and thermal gravimetric analyses. All three compounds are isostructural and they are formed by isolated [M^II(bpp)₂]²⁺ and [Cr(C₂O₄)₃]³⁻ complexes and free ClO₄ ⁻. As expected, only the salt [Fe(bpp)₂]₂[Cr(C₂O₄)₃]ClO₄·5H₂O shows a thermal spin transition with transition temperature (T_1/2) around 375 K that is correlated to the loss of water molecules.     

Crystal structure of a new vanadate variety in the lomonosovite group: Na5Ti2O2[Si2O7](VO4)

The title compound has been prepared by a flux crystallisation method and its crystal structure was determined by single crystal X-ray diffraction: space group P, a=5.309(1), b=7.133(1), c=14.746(2) Å, α=99.05(1), β=95.97(1), γ=90.08(1)°, wR₂=0.073, R=0.028. The structure may be described as built by seidozerite modules of composition Na₂Ti₂O₂Si₂O₇ — brucite-type layers of [TiO₆] and [NaO₆] octahedra embedded between layers of [TiO₆] octahedra, [Si₂O₇] groups and [NaO₈] polyhedra. These almost centrosymmetrical triple-layers alternate along the c-axis with polar double-layer-modules of composition Na₃VO₄ formed by isolated [VO₄]³⁻ anions and six- and four-coordinate Na cations. The crystal structure is discussed in context with minerals of the lomonosovite group. The thermal decomposition behaviour suggests a decay to the single modular components Na₂Ti₂O₂Si₂O₇ and Na₃VO₄.     

Synthesis,structure and magnetic properties of pyrazolate-bridged dinuclear complexes [{M(NCS)(4-Phpy)}2(μ-bpypz)2] (M = Co2+ and Fe2+)

The synthesis and magnetic characterization of pyrazolato-bridged dinuclear complexes [{M(NCS)(4-Phpy)}₂(μ-bpypz)₂] (Hbpypz = 3,5-bis(2-pyridyl)-pyrazole; 4-Phpy = 4-phenylpyridine; M = Co²⁺ (1) and Fe²⁺ (2)) are described together with the X-ray crystal analysis of the cobalt complex. The structure of 1 shows that the desired coordination has been achieved with the cobalt atoms being coordinated to two bpypz to form the dimer. The X-ray diffraction patterns show 1 and 2 to be isomorphous at room temperature. 2 displays a single spin-crossover transition between the [HS–HS] and [LS–LS] states with T_c = 150 K.     

Synthesis,molecular structure,vibrational studies,optical properties and electrical conduction mechanism of the new hybrid compound based on selenate

The new hybrid material tetrapropylammonium hydrogen selenate bis (selenic acid), N(C₃H₇)₄[HSeO₄][H₂SeO₄]₂ (hereafter abbreviated TPSe) has been synthesized by slow evaporation technique at room temperature. Crystal structure, DTA-TGA measurements, Raman, Infrared spectroscopy, nuclear magnetic resonance (NMR) electrical properties, and optical properties were provided to characterize the TPSe. This crystal structure contains one organic cation [N(C₃H₇)₄]⁺, one [HSeO₄]⁻ tetrahedra, and two neutral selenic acids H₂SeO₄. The inorganic [HSeO₄]⁻ and H₂SeO₄ species consist of infinite two-dimensional inter-linkers via strong hydrogen bonds (O-H⋯O), giving birth to trimmers [(H₂SeO₄)₂ HSeO₄]_nⁿ⁻. The IR and Raman spectra of the compound recorded at room temperature were studied in regard to the literature data, and on the basis of theoretical group analysis. The theoretical calculations using the density functional theory DFT at the B3LYP/6-31G(d) level, are made to study the optimized molecular structure, the vibrational spectra, and the optical properties of TPSe compound. Good agreements were found between the theoretical results and the experimental Raman, IR spectra and the molecular structure. The polarizability α, the hyperpolarizability β, and the electric dipole μ calculated using DFT/B3LYP-31G(d) exhibit the non-zero hyperpolarizability β of the TPSe, indicating that this material could be used in certain NLO applications. The thermal DTA-TGA analyses did not show any phase transition in the 333–500 K temperature domain. The complex impedance spectroscopy is measured and discussed in the temperature (290–363 K) and frequency (1 kHz−13 MHz) domains to study the electrical propreties of the compound.     

Solid state coordination chemistry of the copper(II)/bisterpy/vanadate system: The structures of [Cu2(bisterpy)V4O12]·2H2O and [Cu2(bisterpy)V4F2O11] (bisterpy = 2,2′:4′,4′′:2′′,2′′′-quarter-pyridyl, 6′,6′′-di-2-pyridine)

Hydrothermal methods were exploited in the preparation of bimetallic organic–inorganic hybrid materials of the metal-bisterpy/vanadate class. [Cu₂(bisterpy)V₄O₁₂]·2H₂O exhibits a two-dimensional structure constructed from {Cu₂V₄O₁₂}_n chains linked through bisterpy ligands. The isomorphous materials [M₂(bisterpy)V₄F₂O₁₁] (M = Cu, Zn) are also two-dimensional. In these cases, {M₂V₄F₂O₁₁}_n chains are linked through bisterpy ligands to generate the two-dimensional network.     

Structure and photoluminescence properties of Ce-doped novel silicon-oxynitride Ba4−zMzSi8O20−3xN2x (M=Mg, Ca, Sr)

Structural and photoluminescence properties of undoped and Ce³⁺-doped novel silicon-oxynitride phosphors of Ba_4−zM_zSi₈O_20−3xN_2x (M=Mg, Sr, Ca) are reported. Single-phase solid solutions of Ba_4−zM_zSi₈O_20−3xN_2x oxynitride were synthesized by partial substitutions of 3O²⁻→2N³⁻ and Ba→M (M=Mg, Ca, Sr) in orthorhombic Ba₂Si₄O₁₀. The influences of the type of alkaline earth ions of M, the Ce³⁺ concentration on the photoluminescence properties and thermal quenching behaviors of Ba₃MSi₈O_20−3xN_2x (M=Mg, Ca, Sr, x=0.5) were investigated. Under excitation at about 330 nm, Ba₃MSi₈O_20−3xN_2x:Ce³⁺ (x=0.5) exhibits efficient blue emission centered at 400-450 nm in the range of 350-650 nm owing to the 5d→4f transition of Ce³⁺. The emission band of Ce³⁺ shifts to long wavelength by increasing the ionic size of M due to the modification of the crystal field, as well as the Ce³⁺ concentrations due to the Stokes shift and energy transfer or reabsorption of Ce³⁺ ions. Among the silicon-oxynitride phosphors of Ba₃MSi₈O_18.5N:Ce³⁺, M=Sr_0.6Ca_0.4 possesses the best thermal stability probably related to its high onset of the absorption edge of Ce³⁺.     

Synthesis and characterization of manganese and cobalt pyroborates: M2B2O5 (M = Mn,Co)

The magnetic property of Co₂B₂O₅ and the optical property of M₂B₂O₅ (M = Mn, Co) were investigated. Co₂B₂O₅ showed antiferromagnetic behavior below the Néel temperature of T_N ≈ 45 K, and the Weiss temperature was T_W = +7.7 K. The effective magnetic moment of Co was 4.96 μ_B, which indicated that Co was divalent and in a high-spin state. Absorptions attributed to the d–d transitions in Mn²⁺ and Co²⁺ ions were observed at 250–650 nm in the diffuse reflection spectra. The optical absorption edges of Mn₂B₂O₅ and Co₂B₂O₅ were at 243 nm (5.11 eV) and 299 nm (4.15 eV), respectively.     

A New Main Group Metal Coordination Polymer: Synthesis,Structure, and Dielectric Constant Property of [Na(C6H4N5)(H2O)2]n

The reaction of NaOH with 4‐(2H‐tetrazol‐5‐yl)pyridine affords the first tetrazole‐pyridine sodium coordination polymer with chain structure, [Na(C₆H₄N₅)(H₂O)₂]_n ( 1 ). The compound could be characterized by single‐crystal X‐ray diffraction analysis. The temperature dependence of dielectric permittivity remains unchanged almost within the measured temperature range of 80 K to 270 K at 1 <SC>MH</SC>z, and the frequency dependence of the permittivity showed rapidly drops from 31.5 to 4.3 within the measured frequency range of 200 to 1 MHz at room temperature.     

Densities and refractive indices of imidazolium- and phosphonium-based ionic liquids: Effect of temperature,alkyl chain length,and anion

A systematic study of densities and refractive indices of 17 room temperature ionic liquids is presented at four different temperatures ranging from 293 K to 333 K. The ionic liquids are grouped into four families: 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [C_nmim][Ntf₂], ionic liquids (with n = 2, 4, 6, 8, 10, 12, and 14); 1-alkyl-3-methylimidazolium hexafluorophosphate, [C_nmim][PF₆], ionic liquids (with n = 4, 6, 8); ionic liquids based on the trihexyl(tetradecyl)phosphonium cation, [P_{6 6 6 14}], combined with the anions bis(trifluoromethylsulfonyl)amide, [Ntf₂], acetate, [OAc], and triflate, [OTf]; and [C₄mim]-based ionic liquids combined with the anions [OAc], [OTf], methylsulfate [MeSO₄], and tetrafluoroborate [BF₄]. The data obtained were analysed to determine the effect of (i) temperature, (ii) the alkyl chain length of the 1-alkyl-3-methylimidazolium cation, and (iii) the nature of the anion. Different empirical models for the calculation of the densities of the ionic liquids were tested. Molar refractions were also calculated from the volumetric and refractive index data and the values were discussed with the aim of checking their utility in obtaining insights on the intermolecular forces and behaviour in solution of the different ionic liquids.