Titanium as a chemical modifier for the determination of cobalt in marine sediments

The determination of cobalt in marine sediments by electrothermal atomic absorption spectrometry was studied using no modifier and magnesium and titanium as modifiers. Titanium is one of the major sediment constituents, which widely affects the cobalt determination and it was studied as a chemical modifier since it was the only concomitant that increased the cobalt signal in the concentration range usually found in sediments. The performance of Mg and Ti as chemical modifiers was compared relative to maximum pyrolysis and atomization temperatures, linear calibration range, sensitivity and matrix effects. The pyrolysis curves showed that the analyte could be stabilized up to 1400 °C when either Ti or Mg(NO₃)₂ was present, while only 1000 °C could be used in the absence of a modifier. The optimum atomization temperature was 2500 °C in all cases. Analytical curves were compared using no modifier, 5 μg Ti and 100 μg Mg(NO₃)₂ as modifiers, and the linear range found was up to approximately 4 ng Co whether a modifier was used or not. With Ti as a chemical modifier, analytical curves for cobalt in aqueous solution and in a synthetic matrix resulted in the same sensitivity (m₀=55 pg), whereas the use of Mg led to characteristic mass values of 59 and 72 pg in aqueous solution and in a synthetic matrix, respectively, showing some matrix effect. The detection limits (3σ, n=10) were 0.4 μg g⁻¹ using no modifier and 0.3 μg g⁻¹ with Ti as a modifier in the original matrix. A reference estuarine sediment NIST 1646 with a non-certified content of 10.5 μg g⁻¹ Co was analyzed and the found value of 10.9±2.4 μg g⁻¹, (n=3), using Ti as chemical modifier and calibration against aqueous standards, was in good agreement with the recommended value.     

Zn(II) complexes with pyridine derived N6 and N8 donor azamacrocyclic ligands

A novel N6 macrocyclic ligand, L¹ (2,8,14,20-tetramethyl-3,7,15,19,25,26-hexaaza-tricyclo[19.3.1.1^9,13]hexacosa-1(24),9,11,13(26),21(25),22-hexaene), was obtained by reduction of the 2 + 2 condensation product of 2,6-diacetylpyridine and propane-1,3-diamine. Zinc(II) complexes of L¹, of a related N8 macrocycle, L³ (3,6,9,17,20,23,29,30-octaaza-tricyclo[23.3.1.1[11,15]]triaconta-1(28),1,13,15(30),25(29),26-hexaene), similarly prepared by 2 + 2 condensation of 2,6-diformylpyridine and diethylenetriamine and of a tetra N-2-cyanoethyl derivative of a homologue of L¹ prepared from diformyl pyridine and ethane-1,2-diamine, L² (3-[6,14,17-tris-(2-cyano-ethyl)-3,6,14,17,23,24-hexaaza-tricyclo[17.3.1.1^8,12] tetracosa-1(23),8(24),9,11,19,21-hexaen-3-yl]-propionitrile), were prepared. Structures were determined for [ZnL¹](ClO₄)₂ · H₂O, [ZnL²](NO₃)₂ and [Zn₂L³(NO₃)₂](NO₃)₂ · H₂O. The [ZnL¹](ClO₄)₂ · H₂O and [ZnL²](NO₃)₂ complexes present a mononuclear endomacrocyclic structure with the metal in an octahedral distorted environment coordinated by the six donor nitrogen atoms from the macrocyclic backbone while the complex [Zn₂L³(NO₃)₂](NO₃)₂ · H₂O is dinuclear with both metal atoms into the macrocyclic cavity coordinated by four donor nitrogen atoms from the macrocyclic framework and one oxygen atom from one monodentate nitrate anion, in a distorted square pyramidal arrangement.     

Sintering behavior and apatite formation of diopside prepared by coprecipitation process

Sintering behavior and bioactivity of diopside, CaMgSi₂O₆, prepared by a coprecipitation process were examined for its biomedical applicability. As-prepared powder was synthesized by adding aqueous ammonia to an ethanol solution containing Ca(NO₃)₂·4H₂O, Mg(NO₃)₂·6H₂O, and Si(OC₂H₅)₄ and characterized by means of TG–DTA, XRD, and TG–MS. The dried powder was X-ray amorphous and crystallized into diopside at 845.5 °C. The glass network formation by SiO₄ tetrahedra was almost completed below 800 °C. The bioactivity of the diopside prepared by sintering the compressed powder at 1100 °C for 2 h was evaluated by immersion of the sintered body in a simulated body fluid (SBF) at 36.5 °C. Leaf-like apatite particles were found to be formed on the surface of the sintered body and grew with passage of soaking time. This apatite-forming behavior in the SBF is related to the dissolution of Ca(II) ions from the sintered body in the early stage of immersion. Thus, diopside prepared by the coprecipitation process using the metal alkoxide and the metal salts was found to have an apatite-forming ability.     

The ternary system H2O–Fe(NO3)3–Co(NO3)2 isotherms 0 and 15 °C

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.

Two isotherms were established at 0 and 15 °C, and the stable solid phases which appear are the iron nitrate nonahydrate (Fe(NO₃)₃·9H₂O), the iron nitrate hexahydrate (Fe(NO₃)₃·6H₂O), the cobalt nitrate hexahydrate (Co(NO₃)₂·6H₂O) and the cobalt nitrate trihydrate (Co(NO₃)₂·3H₂O).     

Three interpenetrated frameworks constructed by long flexible N,N′-bipyridyl and dicarboxylate ligands

Three interpenetrated polymeric networks, {[Co(bpp)(OH-BDC)] · H₂O}_n (1) [Ni(bpp)_1.5(H₂O)(OH-BDC)]_n (2) and {[Cd(bpp)(H₂O)(OH-BDC)] · 2H₂O}_n (3), have been prepared by hydrothermal reactions of 1,3-bis(4-pyridyl)propane (bpp), 5-hydroxyisophthalic acid (OH-H₂BDC), with Co(NO₃)₂ · 6H₂O, Ni(NO₃)₂ · 6H₂O and Cd(NO₃)₂ · 4H₂O, respectively. Single-crystal X-ray diffraction analyses reveal that the three compounds all exhibit interpenetrated but entirely different structures. Compound 1 is a fourfold interpenetrated adamantanoid structure with water molecules as space fillers, in which bpp adopts a TG conformation (T = trans, G = gauche). Compound 2 is an interdigitated structure from the interpenetrated long arms of one-dimensional molecular ladders, while bpp in 2 adopts both TT and TG conformations. Compound 3 is a twofold interpenetrated three-dimensional network from a one-dimensional metal-carboxylate chain bridged by TG conformational bpp. The hydrogen bonding interactions in 1–3 further stabilize the whole structural frameworks and play critical roles in their constructions.     

Synthesis and crystal structure of two novel nickel (imidazole) complexes having hydrogen-bonded networks

Two nickel (imidazole) complexes, Ni(im)₆Cl₂·4H₂O (1) and Ni(im)₆(NO₃)₂ (2) (im=imidazole) have been synthesized and characterized by elemental analysis, IR, UV, TG and single crystal X-ray diffraction. 1 crystallizes in the triclinic space group P-1 with a=8.800(6) Å, b=9.081(6) Å, c=10.565(7) Å, =75.058(9)°, β=83.143(8)°, γ=61.722(8)°, V=718.3(8) Å³, Z=1 and R₁ (wR₂)=0.0469 (0.1497). 2 crystallizes in the trigonal space group R-3 with a=12.370(6) Å, b=12.370(6) Å, c=14.782(14) Å, =90.00°, β=90.00°, γ=120.00°, V=1959(2) Å³, Z=3 and R₁ (wR₂)=0.0358 (0.0955). 1 and 2 exhibit different supramolecular network due to their different counter anions and different hydrogen bonding connection. In compound 1, [Ni(im)₆]²⁺ cation and counter anions Cl⁻ alternatively array in an ABAB fashion via N–HCl hydrogen bonding. In compound 2, the plane of each NO₃²⁻ is almost parallel and each NO₃²⁻ connect three different [Ni(im)₆]²⁺ cations via N–HO hydrogen bonding.     

Interaction between Pd and Ag on the surface of silica

Palladium, silver and palladium–silver catalysts supported on silica were prepared by coimpregnation of support with solution of AgNO₃ and Pd(NO₃)₂. The catalysts were characterized by X-ray powder diffraction (XRD), temperature programmed reduction (TPR), time of flight ion mass spectrometry (ToF-SIMS), chemisorption of carbon monoxide and were tested in the reaction of selective oxidation of glucose to gluconic acid.

XRD and TPR studies have shown that an interaction between Pd and Ag on the surface of silica after oxidation at 500 °C and reduction at 260 °C leads to the formation of solid solutions.

ToF-SIMS images of the surface of 5% Ag/SiO₂ catalyst after oxidation at 500 °C and reduction at 260 °C show that Ag atoms supported on silica are not distributed homogenously but tend to form regions of enhanced Ag concentration. Positive ions images of the surface of 5% Pd/SiO₂ catalyst also display regions of enhanced concentration of Pd atoms, but they are more homogenously distributed on silica.

ToF-SIMS peak intensity ratio ¹⁰⁸Pd⁺/¹⁰⁷Ag⁺ for bimetallic 5% Pd–5% Ag/SiO₂ catalysts has a lower value than that obtained for physical mixture 5% Pd/SiO₂–5% Ag/SiO₂ which indicates that the surface of bimetallic catalyst is enriched with silver atoms.     

Ion size dominated 1D and 2D Salen lanthanide coordination complexes and their luminescence

Lewis acid/base addition between Ln(NO₃)₃ · 6H₂O (Ln = Pr, Nd, Sm, Eu, Tb and Lu) and H₂salen [H₂salen = N,N′-ethylenebis(salicylideneimine)] gives rise to an array of coordination polymeric structures. Crystal structural analysis reveals that Salen effectively functions as a bridging ligand in these compounds. The size of the lanthanide ions controls the structures of these Salen lanthanide complexes. Two representative structures with one dimensional and two dimensional topologies, viz. [Pr(H₂salen)(NO₃)₃(CH₃OH)₂]_n (1) and [Ln(H₂salen)_1.5(NO₃)₃]_n [Ln = Pr (2), Nd (3), Sm (4), Eu (5), Tb (6) and Lu (7)] are reported. Luminescent spectra of complexes 4 and 5 exhibit characteristic metal-centered emission lines. However, the characteristic luminescence of the terbium(III) ion is not observed either in solution or in the solid state of complex 6.     

Li2SO4-MgSO4及LiNO3-Mg(NO3)2熔盐体系的研究

用目测变温法和差热分析法研究了Li₂SO₄-MgSO₄、LiNO₃-Mg(NO₃)₂熔盐体系。在前一体系中有固液异组成化合物Li₂SO₄·2MgSO₄生成,它在832°熔化分解。化合物与Li₂SO₄间形成低共熔点,温度为647℃,组成含MgSO₄23.6Wt%。Li₂SO₄多晶转变点575℃,在加入MgSO₄后形成类低共熔点,温度552℃,组成含MgSO₄4.2%。LiNO₃-Mg(NO₃)₂为一简单低共熔体系,共晶点含Mg(NO₃)₂47.3%,温度200℃。     

Influence of electronic and steric effects on stability constants and electrochemical reversibility of divalent ion complexes with glycine and sarcosine. A glass electrode potentiometric, sampled direct current polarographic, virtual potentiometric, and molecular modelling study

Cd^II complexes with glycine (gly) and sarcosine (sar) were studied by glass electrode potentiometry, direct current polarography, virtual potentiometry, and molecular modelling. The electrochemically reversible Cd^II–glycine–OH labile system was best described by a model consisting of M(HL), ML, ML₂, ML₃, ML(OH) and ML₂(OH) (M = Cd^II, L = gly) with the overall stability constants, as log β, determined to be 10.30 ± 0.05, 4.21 ± 0.03, 7.30 ± 0.05, 9.84 ± 0.04, 8.9 ± 0.1, and 10.75 ± 0.10, respectively. In case of the electrochemically quasi-reversible Cd^II–sarcosine–OH labile system, only ML, ML₂ and ML₃ (M = Cd^II, L = sar) were found and their stability constants, as log β, were determined to be 3.80 ± 0.03, 6.91 ± 0.07, and 8.9 ± 0.4, respectively. Stability constants for the ML complexes, the prime focus of this work, were thus established with an uncertainty smaller than 0.05 log units. The observed departure from electrochemical reversibility for the Cd–sarcosine–OH system was attributed mainly to the decrease in the transfer coefficient . The MM2 force field, supplemented by additional parameters, reproduced the reported crystal structures of diaqua-bis(glycinato-O,N)nickel(II) and fac-tri(glycinato)-nickelate(II) very well. These parameters were used to predict structures of all possible isomers of (i) [Ni(H₂O)₄(gly)]⁺ and [Ni(H₂O)₄(sar)]⁺; and (ii) [Ni(H₂O)₃(IDA)] and [Ni(H₂O)₃(MIDA)] (IDA = iminodiacetic acid, MIDA = N-methyl iminodiacetic acid) by molecular mechanics/simulated annealing methods. The change in strain energy, ΔU_str, that accompanies the substitution of one ligand by another (ML + L′ → ML′ + L), was computed and a strain energy ΔU_str = +0.28 kcal mol⁻¹ for the reaction [Ni(H₂O)₄(gly)]⁺ + sar → [Ni(H₂O)₄(sar)]⁺ + gly was found. This predicts the monoglycine complex to be marginally more stable. By contrast, for the reaction [Ni(H₂O)₃IDA] + MIDA → [Ni(H₂O)₃MIDA] + IDA, ΔU_str = −0.64 kcal mol⁻¹, and the monoMIDA complex is predicted to be more stable. This correlates well with (i) stability constants for Cd–gly and Cd–sar reported here; and (ii) known stability constants of ML complex for glycine, sarcosine, IDA, and MIDA.     

A convenient catalytic approach to synthesize straight boron nitride nanotubes using synergic nitrogen source

Straight boron nitride nanotubes (BNNTs) with pure hexagonal phase were conveniently prepared by heating the mixture of Mg(BO₂)₂ · H₂O, NH₄Cl, NaN₃ and Mg powder in an autoclave at 600 °C for 20–60 h. These BNNTs had diameters mainly ranging 30–300 nm and lengths up to 5 μm, and a majority of them had at least one closed end. Besides the traditional end tips, additional cone-like tips were frequently found to be attached on the BNNTs. The effects of temperature, reactants and the possible mechanism of the catalytic formation of the BNNTs are discussed.     

Enhanced Corrosion Resistance and Discharge Performance of Mg-MnO2 Battery by Na2SiO3 Additive

Corrosion resistance and delayed action are major obstacles that severely limit the practical application of Mg alloy in battery fields. In this work, the effects of Na2SiO3 on the electrochemical behavior of the AZ31B Mg alloy in MgSO4-Mg(NO3)2 composite solution[0.14 mol/L MgSO4,1.86 mol/L Mg(NO3)2] were investigated. Electrochemical tests were carried out using electrochemical impedance spectroscopy, galvanostatic discharge, and linear sweep voltammograms. The results indicate that the impedance value increases by nearly fourfold, and the delayed time decreases from 2.1 s to 0.6s. Battery perfoniiance test reveals that the addition of Na2SiO3 significantly improves the discharge specific capacity of Mg-MnO2. The surface morphology and composition of corrosion products from Mg alloys were studied by scanning electron microscopy(SEM) and Fourier translonn infrared spectroscopy(FTIR), respectively. The SEM images of the AZ31B Mg alloys in composite solution with or without Na2SiO3 additive have an evident distinction due to the ionnation of new insoluble compound.FTIR result confirms that the corrosion products accumulated on the alloy surface in the electrolyte containing Na2SiO3 are mainly composed of Mg(OH)2, MgCO3, and MgSiO3.     

Syntheses and X-ray crystal structures of [Co(η-CO3)(NH3)4](NO3)·0.5H2O and [(NH3)3Co(μ-OH)2(μ-CO3)Co(NH3)3][NO3]2·H2O

[Co(η²-CO₃)(NH₃)₄](NO₃)·0.5H₂O and [(NH₃)₃Co(μ-OH)₂(μ-CO₃)Co(NH₃)₃][NO₃]₂·H₂O were prepared by prolonged aerial oxidation of a solution of Co(NO₃)₂·6H₂O and ammonium carbonate in aqueous ammonia. The formation of these side products highlights the richness of the chemistry of these systems and the possibility of by products if methods are not strictly adhered to. The X-ray crystal structures of [Co(η²-CO₃)(NH₃)₄][NO₃]·0.5H₂O and [(NH₃)₃Co(μ-OH)₂(μ-CO₃)Co(NH₃)₃][NO₃]₂·H₂O reveal a monomeric octahedral cobalt center with η²-bound CO₃²⁻ in the former, while the latter consists of a dimeric array where the two cobalt centers are bridged by two OH⁻ and one μ₂-CO₃²⁻ groups with three terminal NH₃ ligands for each Co center. In both complexes extensive hydrogen bonding interactions are evident.     

Homochiral cobalt(II) and strontium(II) amino-carboxylate–phosphonate hybrids

Two homochiral metal amino-carboxylate–phosphonate hybrids, namely, [Co₂Cl(S-HL)(H₂O)₅]Cl · H₂O 1 and Sr₂(S-HL)(NO₃)₂(H₂O) · H₂O 2 (S-H₃L = S-HO₂CC₄H₇NCH₂PO₃H₂) have been synthesized by the reaction of the enantiopure S-H₃L ligand with cobalt(II) chloride or strontium nitrate under acidic condition at room temperature. The structure of compound 1 features a novel 3D framework with helical chains and channels. Compound 2 has a layered structure in which the 1D chains of edge-sharing SrO₈ and SrO₉ polyhedra are interconnected by phosphonate ligands.     

金属氧化物和盐催化剂上尿素与甲醇合成碳酸二甲酯

在高压釜中采用金属氧化物和盐作为催化剂由尿素与甲醇合成碳酸二甲酯。结果表明,含有结晶水的金属盐比无结晶水金属盐和金属氧化物具有更好的催化活性。采用羟基化合物与硝酸锌组成的二元催化剂,其催化活性显著高于单一催化剂;羟基与硝酸锌之间具有协同催化作用。其中,硝酸锌与SiO2组成的二元催化剂活性最高;硝酸锌与SiO2的质量比为2时,DMC收率可达4.5%。     

Fabrication of novel threefold shape CeO2 dendrites: Optical and electrochemical properties

Threefold shape CeO₂ dendritic crystals were successfully prepared from a single precursor via a thermal decomposition route. The precursor was synthesized by a hydrothermal reaction using Ce(NO₃)₃6 H₂O with CO(NH₂)₂ at 150 °C in a water–TEA complex solution. The dendritic pattern of precursor almost remained in the as-prepared product. The optical absorption spectrum indicates that the CeO₂ dendrites have a direct band gap of 3.51 eV. The electrochemical tests show that the CeO₂ dendrites are a promising electrode material as they can deliver a large reversible discharge capacity of about 534 mAh g⁻¹.     

Rate constant of the reaction of NO3 with CH2I2 measured with use of cavity ring-down spectroscopy

We have applied cavity ring-down spectroscopy to a kinetic study of the reaction of NO₃ with CH₂I₂ in 25–100 Torr of N₂ diluent at 298 K. The rate constant of reaction of NO₃ + CH₂I₂ is determined to be (4.0 ± 1.2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ in 100 Torr of N₂ diluent at 298 K. The rate constant increases with increasing pressure of buffer gas below 100 Torr. The reaction of CH₂I₂ with NO₃ has the potential importance at nighttime in the atmosphere.     

Syntheses and structural characterization of transition metal(II) coordination polymers containing 4,4′-dipyridyldisulfide

The reactions of Zn(NO₃)₂ · 6H₂O and FeSO₄ · 7H₂O with 4-PDS (4-PDS = 4,4′-dipyridyldisulfide) and NH₄SCN in CH₃OH afforded the complexes [Zn(NCS)₂(4-PDS)]_n (1) and [Fe(NCS)₂(4-PDS)₂ · 4H₂O]_n (2), respectively, while the reaction of CoCl₂ · 6H₂O with 4-PDS in CH₃OH gave the complex {[Co(4-PDS)₂][Cl]₂ · 2CH₃OH}_n, (3). These complexes have been characterized by spectroscopic methods and their structures determined by X-ray crystallography. The 4-PDS ligands in 1 are coordinated to the metal centers through the nitrogen atoms to form 1-D zigzag-chains, and the distorted tetrahedral coordination geometry at each zinc center is completed by a pair of N-bonded thiocyanate ligands. Compound 2 has a 1-D channel-chain structure and each octahedral Fe(II) metal center is coordinated by four 4-PDS ligands and two trans N-bonded thiocyanate ligands. Weak SS interactions in complex 1 link the 1-D chains into 2-D molecular sheets. In complex 2, the channel chains are interlinked through SS interactions to form molecular sheets, which interpenetrate through the SS interactions to form 3-D structures with large cavities that are occupied by the water molecules. Compound 3 also has a 1-D channel-chain structure with each square-planar Co(II) metal center coordinated by four 4-PDS ligands. Multiple C–HCl hydrogen bonds and SO interactions in 3 link the 1-D chains into 2-D structures.     

Tetrakis(triphenylphosphine oxide) complexes of the lanthanide nitrates; synthesis, characterisation and crystal structures of [La(Ph3PO)4(NO3)3]·Me2CO and [Lu(Ph3PO)4(NO3)2]NO3

The reaction of Ln(NO₃)₃·6H₂O (Ln=La, Ce, Pr or Nd) with a sixfold excess of Ph₃PO in acetone formed [Ln(Ph₃PO)₄(NO₃)₃]·Me₂CO. The crystal structure of the La complex shows a nine-coordinate metal centre with four phosphine oxides, two bidentate and one monodentate nitrate groups, and PXRD studies show the same structure is present in the other three complexes. In CH₂Cl₂ or Me₂CO solutions, ³¹P NMR studies show that the complexes are essentially completely decomposed into [Ln(Ph₃PO)₃(NO₃)₃] and Ph₃PO. Similar reactions in ethanol gave [Ln(Ph₃PO)₃(NO₃)₃] only. In contrast for Ln=Sm, Eu or Gd, only the [Ln(Ph₃PO)₃(NO₃)₃] are formed from either acetone or ethanol solutions. For the later lanthanides Ln=Tb–Lu, acetone solutions of Ln(NO₃)₃·6H₂O and Ph₃PO gave [Ln(Ph₃PO)₃(NO₃)₃] only, even with a large excess of Ph₃PO, but from cold ethanol [Ln(Ph₃PO)₄(NO₃)₂]NO₃ (Ln=Tb, Ho–Lu) were obtained. The structure of [Lu(Ph₃PO)₄(NO₃)₂]NO₃ shows an eight-coordinate metal centre with four phosphine oxides and two bidentate nitrate groups. In solution in CH₂Cl₂ or Me₂CO the tetrakis-complexes show varying amounts of decomposition into mixtures of [Ln(Ph₃PO)₃(NO₃)₃], [Ln(Ph₃PO)₄(NO₃)₂]NO₃ and Ph₃PO as judged by ³¹P{¹H} NMR spectroscopy. The [Ln(Ph₃PO)₃(NO₃)₃] also partially decompose in solution for Ln=Dy–Lu, forming some tetrakis(phosphine oxide) species.     

Ligation properties of 2-acetyl-2-thiazoline semicarbazone (ATsc): Isolation, spectroscopic and X-ray study of ATsc and its Cu(II) and Ni(II) complexes

A new ligand, 2-acetyl-2-thiazoline semicarbazone (ATsc), has been prepared and characterized by a variety of physico-chemical techniques. Likewise, the metal complexes [CuCl₂(ATsc)] and [Ni(ATsc)₂](NO₃)₂ · H₂O have been isolated and characterized through elemental analysis, IR, UV–Vis–NIR diffuse reflectance and magnetic susceptibility, as well as, in the case of the copper complex, by means of EPR. Moreover, the structures have been determined by X-ray diffraction. In both complexes the Schiff base acts as a tridentate ligand through N(1), N(2) and O atoms, making two five-membered chelate rings. The copper complex consists of monomeric molecules in which the copper atom is five coordinated in a distorted square-pyramidal geometry, with one ATsc and two chlorine ligands. The complex cation of nickel possesses approximately a non-crystallographic C₂ symmetry. The environment around the nickel atom may be described as a distorted octahedral geometry with the metallic atom coordinated to two ATsc ligands.