Synthesis,crystal structure,and magnetic property of a stepped tetranuclear copper(II) complex of 3,5-diisopropylpyrazole-1-methoxide

Reaction of copper(II) chloride dihydrate in methanol with deprotonated 3,5-diisopropylpyrazole-1-methanol (dippmOH) led to the tetranuclear copper(II) complex [(dippmO)CuCl]₄ (1). The crystal structure of 1 indicates that two copper(II) ions connect via the oxygen atoms of dippmO⁻ ligands each other in which two dimeric units are formed. Furthermore, one of the coordinated oxygen atoms in a dimer is bonded to an adjacent copper(II) ion positioned other dimer, which gives rise to a stepped tetranuclear structure. 1 shows strong antiferromagnetic interactions through the oxo groups within the dimeric units (J₁ = − 239 cm^− 1) and weak antiferromagnetic couplings between the dimers (J₂ = − 15 cm^− 1).     

Ion implantation and anneal to produce low resistance metal–diamond contacts

Contacts to boron-doped, (100)-oriented diamond implanted with Si or with Si and B were formed and the effects of dose, implantation energy and anneal treatment on the specific contact resistance were examined. Ti/Au contacts on heavily implanted diamond (10¹⁶ Si ions cm⁻², E_i=30 keV or 10¹⁷ Si and B ions cm⁻², E_i=15 keV (Si) and E_i=10 keV (B)) had a specific contact resistance lower than the best contacts produced on unimplanted diamond. A specific contact resistance of (1.4±6.4)×10⁻⁷ Ω cm⁻² was achieved following a 450°C anneal. The results were consistent with a reduction in barrier height brought about by silicide formation. Light silicon implantation (10¹³ ions cm⁻²) or relatively light dual implantation (B, Si<10¹⁶ ions cm⁻²) did not reduce the specific contact resistance. Increasing the diamond conductivity by 4×10⁴ decreased the specific contact resistance by over three orders of magnitude, in agreement with the trend observed by Prins (J.F. Prins, J. Phys. D 22 (1989) 1562).     

Assembly of an imidazole templated indium-oxalate porous 3D framework with tcj/hc topology: Synthesis,structure and sorption property

A 3D In(III) metal organic framework {[(CH₃)₂NH₂][In₂(Ox)_3.5(Im)]∙H₂O∙DMF}_n (1) (Ox = oxalic acid, Im = imidazole) which is templated by imidazole molecules has been synthesized solvothermally. Compound 1, is an anionic framework with 1D open channels which are filled with (CH₃)₂NH₂⁺, DMF and water molecules. The network exhibits a 3,4-c binodal net with a rare tcj/hc topology. The total solvent accessible volume in the crystal is 43.2%. Sorption studies show that it can adsorb a maximum amount of 47 cm³ g^− 1 of CO₂ gas at 195 K while the uptake of N₂ and CH₄ is negligible.     

Ferromagnetic interactions in zinc(II) coordination complex containing nitronyl nitroxide radicals

A novel complex Zn(NIT2-py)₃(ClO₄)₂(NIT2-py = 2-(2′-pyridyl)-4,4,5,5-tetramethyl-2-imidazoline-1-oxyl-3-oxide) (1) has been synthesized and characterized structurally and magnetically. The metal coordination sphere is fully occupied by three chelating nitroxide ligands, showing a distorted octahedral geometry. Temperature dependence of susceptibility measurements shows a weak ferromagnetic coupling between NIT2-py radicals with J = 2.13 cm⁻¹. The field dependence of the magnetization further confirms that the ground state of the compound S = 3/2 results from ferromagnetic interactions within the complex 1.     

Synthesis,structure, and substitution reactivity of a new bi-oxo capped molybdenum cluster: [Mo3(μ3-O)2(μ-O2CCH2Cl)6(H2O)2(OH)]+

A new bi-oxo capped molybdenum carboxylate, [Mo₃(μ₃-O)₂(μ-O₂CCH₂Cl)₆(H₂O)₂(OH)]⁺, was synthesized by refluxing [Mo₃(μ₃-O)₂(μ-O₂CCH₃)₆(H₂O)₃]^2 + in chloroacetic acid for 20 h (T = 110 °C). Using ion-exchange chromatography (0.5 M NaClO₄ eluant), the trinuclear molybdenum ion was isolated and allowed to crystallize slowly (T = 4 °C) as the perchlorate salt (yield 23%). Upon dissolution of the compound in methanol-d₄, substitution of the terminal ligands for solvent occurs readily in which the observed exchange rate constant is k_obs^298K = 5.3 × 10^− 5 (± 0.3) s^− 1 and activation parameters equal to ΔH³ = 130 (± 10) kJ mol^− 1 and ΔS³ = 111 (± 33) J mol^− 1 K^− 1. From the kinetic data, we find that ligand substitution follows a dissociative pathway and that rates of substitution are faster than expected when compared to the molybdenum acetate analog. Herein, we report the synthesis, crystallographic study, and substitution reactivity of a new molybdenum bi-oxo capped cluster with bridging chloroacetate ligands.     

Enhancement of pyroelectric properties of lead-free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics by La doping

Lead-free 0.94NBT-0.06BT-xLa ceramics at x = 0.0–1.0 (%) were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. With increasing La³⁺ content pyroelectric coefficient (p) and figures of merits greatly increase; however, the depolarization temperature (T_d) decreases. p is 7.24 × 10⁻⁴C m⁻² °C⁻¹ at RT at x = 0.5% and 105.4 × 10⁻⁴C.m^−2 °C⁻¹ at T_d at x = 0.2%. F_i and F_v show improvements at RT from 1.12 (x = 0%) to 2.65 (x10 ⁻¹⁰ m v⁻¹) (x = 0.5%) and from 0.021 to 0.048 (m².C⁻¹) respectively. F_i and F_v show a huge increase to 37.6 × 10⁻¹⁰ m v⁻¹ and 0.56 m² C⁻¹ respectively at T_d at x = 0.2%. F_C shows values of 2.10, 2.89, and 2.98 (x10⁻⁹C cm⁻² °C⁻¹) at RT at 33, 100 and 1000 (Hz) respectively. Giant pyroelectric properties make NBT-0.06BT-xLa at x = 0.2% and 0.5% promising materials for many pyroelectric applications.     

New μ-oxo-bridged tetranuclear Cu(II) complex with Schiff-base ligand: Synthesis,crystal structure and magnetic properties

A new μ-oxo-bridged Cu(II) complex with cubane-like tetranuclear copper(II) complex, [Cu₄(L¹)₄] · 4H₂O (1) (H₂L¹ = 2-(3-methoxy-salicylidene-amino)-benzyl-alcohol), has been prepared, and structurally characterized by X-ray crystallography. Complex 1 crystallized in the monoclinic space group P₂₁/n and has a tetranuclear core of Cu₄O₄. The temperature dependence of magnetic susceptibility measurements shown that complex 1 exhibits a strong antiferromagnetic interaction with J = −103.4 cm⁻¹.     

Hydrothermal syntheses and characterization of a series of mixed-ligand luminescent CdII frameworks with novel 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl) acetate ligand and benzenedicarboxylate isomers

Under similar hydrothermal synthetic conditions using a novel flexible ligand 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)acetonitrile (PPAN), benzenedicarboxylate isomers (H₂pa = phthalate, H₂ip = isophthalate, and H₂tp = terephthalate) and Cadmium(II) acetate, three novel mixed-ligand Cd(II) coordination polymers {[Cd₂(PPAA)₂(μ-pa)(H₂O)]·2H₂O}_n (1), {[Cd₄(PPAA)₄ (μ₄-ip)₂]·2H₂O}_n (2) and {[Cd₂(PPAA)₂(μ-tp)]·2H₂O}_n (3) (PPAA⁻ = 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl) acetate) have been isolated, in 1–3 PPAN, and are also hydrolyzed into a novel PPAA⁻ ligand. Complex 1 is a 1D coordination polymer in which the tetra-nuclear [Cd₄(PPAA)₄]^4 + structural units are extended by tri-dentate μ-pa^2 − ligands. Complex 2 contains binuclear [Cd₂(PPAA)₂]^4 + structural units, which are extended by four tetra-dentate μ₄-ip^2 − ligands to link eight neighboring binuclear [Cd₂(PPAA)₂]^4 + units ultimately forming a 2D layered framework, while complex 3 contains 1D double chain containing [Cd(PPAA)]_n cation structural units, which are further extended by tetradentate μ-tp^2 − ligands to form a new 2D layered framework. All the complexes have been investigated by elemental analysis, FT-IR, thermal analysis and fluorescence characterization. The flexible coordination modes of PPAA⁻ are also briefly analyzed. The flexible coordination modes of PPAA⁻ and benzenedicarboxylate isomers also reveal great potential in the construction of these novel mixed-ligand luminescent frameworks with diverse structural motifs and unique functional properties.     

Magnetostructural study of tetracoordinate cobalt(II) complexes

Five tetracoordinate cobalt(II) complexes of the formula [CoX₂L₂] have been investigated by SQUID magnetometry; X is the (pseudo)halide ligand and L is the N- or P-donor ligand. The complexes exhibit a moderate magnetic anisotropy expressed by the zero-field splitting parameter D. Its value ranges as D/hc = −13 to + 5 cm 21 −1. The value of the D-parameter increases with the angular deformation δ that measures a deviation of the X–Co–X and L–Co–L angles with respect to the ideal tetrahedron.     

Ionic conductivity of Mn2+ doped dense tin pyrophosphate electrolytes synthesized by a new co-precipitation method

Mn²⁺-doped Sn_1−xMn_xP₂O₇ (x = 0–0.2) are synthesized by a new co-precipitation method using tin(II)oxalate as tin(IV) precursor, which gives pure tin pyrophosphate at 300 °C, as all the reaction by-products are vaporizable at <150 °C. The dopant Mn²⁺ acts as a sintering aid and leads to dense Sn_1−xMn_xP₂O₇ samples on sintering at 1100 °C. Though conductivity of Sn_1−xMn_xP₂O₇ samples in the ambient atmosphere is 10⁻⁹–10⁻⁶ S cm⁻¹ in 300–550 °C range, it increases significantly in humidified (water vapor pressure, pH₂O = 0.12 atm) atmosphere and reaches >10⁻³ S cm⁻¹ in 100–200 °C range. The maximum conductivity is shown by Sn_0.88Mn_0.12P₂O₇ with 9.79 × 10⁻⁶ S cm⁻¹ at 550 °C in ambient air and 2.29 × 10⁻³ S cm⁻¹ at 190 °C in humidified air. It is observed that the humidification of Sn_1−xMn_xP₂O₇ samples is a slow process and its rate increases at higher temperature. The stability of Sn_1−xMn_xP₂O₇ samples is analyzed.     

Reversible water inclusion in a porous magnetic material synthesized from copper(II) incorporated metal-organic framework showing alternate ferro- and antiferromagnetic interactions

X-ray structural analysis shows that {[Cu₂(CTA) (H₂O)] · 5 H₂O}_n constitutes infinite one-dimensional parallel chains along the c-axis with water columns running down the crystallographic a-axis. The inclusion of water molecules is reversible and is confirmed by X-ray powder diffraction studies. The magnetic data (2–300 K) reveal that there are alternate ferro- (J = 0.29 cm⁻¹) and antiferromagnetic (J = −2.5 cm⁻¹) interactions.     

A four-spin ring with alternating magnetic interactions formed by pyridine-substituted nitronyl nitroxide radicals and Gd(III) ions: Crystal structure and magnetic properties

A novel complex, [Gd(hfac)₃(NIT-5-Br-3py)]₂ (hfac = hexafluoroacetylacetonat, NIT-5-Br-3py = 2-(4,4,5,5-tetramethyl-3-oxylimidazoline-1-oxide)-5-bromo-3-pyridine) has been synthesized and characterized structurally and magnetically, in which a NIT-5-Br-3py molecular acts as a bridge ligand linking two Gd(III) ions through the oxygen atom of the N–O group and nitrogen atom from the pyridine ring to form a four-spin system. The fitting result of the magnetic susceptibility shows two different magnetic interactions between Gd(III) ion and NIT-5-Br-3py in one complex: a weak ferromagnetic interaction (J₁ = +2.60 cm⁻¹) through the N–O group, and a much weaker antiferromagnetic (J₂ = −0.24 cm⁻¹) interaction through pyridine ring.     

Structural characterization of ferromagnetic bridged-acetato and -dichlorido copper(II) complexes based on bicompartmental 4-t-butylphenol

The reaction of Cu(II) salts with 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-t-butylphenol (L^t-Bu-OH) afforded two bridged-phenoxido/hydroxido complexes. The dinuclear bridged acetate species [Cu₂(μ-L^t-Bu-O)(μ-CH₃COO)](PF₆)₂ (1) and the 1D polymeric doubly-bridged-chlorido {[Cu₂(μ-L^t-Bu-OH)(μ-Cl)₂](ClO₄)₂·4H₂O}_n (2). The two complexes were structurally characterized. Both complexes revealed ferromagnetic interactions; moderate in complex 1 (J = + 30.8 cm^− 1) and very weak (J = + 2.25 cm⁻¹) in 2.     

Improving the POM performance of YBa2Cu3O7−δ membrane reactor by Co doping

The performance of Co doped YBa₂Cu₃O_7−δ (YBCO) membrane reactor have been investigated in a process of the partial oxidation of methane (POM) to syngas. The results shows that doping YBCO membrane with a little Co can enhance its oxygen permeation flux and improve its stability in reducing atmosphere noticeably. At 900 °C, with feed flow at 50 ml/min, CH₄ 6.0 v%, SV = 12,000 h⁻¹, and Ni/ZrO₂ catalyst, CH₄ conversion rate, CO selectivity, and oxygen permeation flux can reach to 98%, 92% and 1.41 ml min⁻¹ cm⁻² respectively.     

Synthesis,crystal structure and magnetic properties of a new cyanide-bridged mixed-valence copper(I)/copper(II) clathrate

A unique cyanide-bridge mixed-valence Cu^I/Cu^II clathrate of formula [Cu^I₂(CN)₃][{Cu^II(tren)}₂(μ-CN)](CF₃SO₃)₂ [tren = tris(2-aminoethyl)amine] containing cyanide-bridged [{Cu^II(tren)}₂(μ-CN)]^3 + binuclear cations stacked between anionic honeycomb layered copper(I) cyanide networks, was synthesized and structurally characterized by single crystal X-ray diffraction. Variable-temperature magnetic susceptibility studies showed that the cyanide bridge mediates a strong antiferromagnetic interaction between the copper(II) centers (J = − 160 cm^− 1, the spin Hamiltonian being defined as H = −J S_A⋅S_B).     

Synthesis and characterization of nickel phosphonopropionate hybrid materials

Hydrothermal reaction of nickel acetate with 3-phosphonopropionic acid and 4,4′-bipyridine resulted in two novel phosphonate compounds Ni(HO₃PC₂H₄COO)(4,4′-bpy)(H₂O) · 0.5(4,4′-bpy) (bpy = bipyridine) (I) and Ni(O₃PC₂H₄COOH)(4,4′-bpy)(H₂O)₃ · H₂O (II). Single-crystal X-ray studies reveal that self-assemblies between the ligands and metal ion result in layer (I) and chain (II) structures. Magnetic measurement of I indicate there are ferromagnetic couplings between adjacent Ni²⁺ ions (C = 1.29 cm³ mol⁻¹ K and θ = 2.25 K).     

Alkoxo- and carboxylato-bridged hexanuclear copper(II) complex: Synthesis,structure and magnetic properties

Reaction of copper(II) nitrate trihydrate with N,N-dimethylethanolamine (dmea) and pivalic acid in methanol led to the hexanuclear copper(II) complex Cu₆(η¹:μ₂-C₄H₁₀NO)₄(η¹:η¹:μ₂-C₅H₉O₂)₄(η¹:μ₁-C₅H₉O₂)₂(μ₃-OH)₂ (1). The crystal structure of 1 indicates that hexametallic centers are bridged by the μ₃-alkoxo, dmea oxygens, and the μ₂-dicarboxylato oxygen atoms of pivalate ions. Furthermore, in the asymmetric unit, three types of copper ions have been found labeled as Cu₁, Cu₂ and Cu₃. The Cu₂ takes a distorted octahedral shape, whereas Cu₁ and Cu₃ adopt square pyramidal geometries. The complex 1 shows strong antiferromagnetic interactions through the oxo groups within the dimeric units (J = − 82.6 to − 25.8 cm^− 1) and weak antiferromagnetic couplings between the dimers (J = − 10.9 and 0.8 cm^− 1).     

Effect of Nd-doping on structural,thermal and electrochemical properties of LaFe0.5Cr0.5O3 perovskites

The structural, thermal and electrochemical properties of the perovskite-type compound La_1−xNd_xFe_0.5Cr_0.5O₃ (x=0.10, 0.15, 0.20) are investigated by X-ray diffraction, thermal expansion, thermal diffusion, thermal conductivity and impedance spectroscopy measurements. Rietveld refinement shows that the compounds crystallize with orthorhombic symmetry in the space group Pbnm. The average thermal expansion coefficient decreases as the content of Nd increases. The average coefficient of thermal expansion in the temperature range of 30–850 °C is 10.12×10⁻⁶, 9.48×10⁻⁶ and 7.51×10⁻⁶ °C⁻¹ for samples with x=0.1, 0.15 and 0.2, respectively. Thermogravimetric analyses show small weight gain at high temperatures which correspond to filling up of oxygen vacancies as well as the valence change of the transition metals. The electrical conductivity measured by four-probe method shows that the conductivity increases with the content of Nd; the electrical conductivity at 520 °C is about 4.71×10⁻³, 6.59×10⁻³ and 9.62×10⁻³ S cm⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. The thermal diffusivity of the samples decreases monotonically as temperature increases. At 600 °C, the thermal diffusivity is 0.00425, 0.00455 and 0.00485 cm² s⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. Impedance measurements in symmetrical cell arrangement in air reveal that the polarization resistance decreases from 55 Ω cm⁻² to 22.5 Ω cm⁻² for increasing temperature from 800 °C to 900 °C, respectively.     

Charge transport properties of single crystal CVD-diamond particle detectors

The charge transport properties of virgin and heavily irradiated intrinsic Single-Crystal CVD-Diamond Detectors (SC-CVD-DD) are discussed by means of the Transient-Current Technique (TCT), which proved to be a sensitive tool to detect the first changes of the detector's performance. Charge-carrier mobilities μ_e = 1300–3100 cm²/V s, μ_h = 2400 cm²/V s and effective deep-trapping lifetimes τ_eff-h = 300–900 ns, τ_eff-e = 160–360 ns were measured in the non-irradiated state, decreasing slightly after irradiation by a fluency F > 10¹³ p_26MeV cm^− 2. The carriers drift velocity remained almost unchanged after irradiation, indicating the creation of mainly neutral defects. After exposure to fluency above 10¹⁶ p cm^− 2 however, TC signals were not detectable with the available broadband electronics. A significant improvement was observed after annealing at 1000 °C, and almost complete restoration was obtained by priming with ⁹⁰Sr-electrons. Optical absorption (OA) spectra confirmed the degradation of the detector performance after exposure to increasing particle fluencies, showing deviations from the intrinsic ‘edge absorption’ shape around 5.3 eV that was observed before irradiation.     

On the stepwise change of activation energies in the hydrodechlorination of chlorobenzene over supported nickel

Kinetics of chlorobenzene hydrodechlorination have been measured over Ni on SiO₂, Al₂O₃, MgO, activated carbon and graphite. A stepwise variation of E_a is analysed using the selective energy transfer model where E_a is identified as the vibrational energy associated with an excitation of the chlorobenzene out-of-plane C–H bending mode. Variation of E_a with vibrational quantum number yields a vibrational frequency of 749 cm⁻¹ and a value (−1.1 cm⁻¹) for the anharmonicity term, which is characteristic of bending vibrational modes. Our analysis suggests that the reacting species are weakly adsorbed on the catalyst: heat of adsorption = −0.31 kJ mol⁻¹.