Studying the Interaction between Water Vapor and a γ-Al2O3 Surface by IR Spectroscopy

Russian Journal of Physical Chemistry A - The interaction between a γ-Al2O3 surface and vapors of H2O and D2O is studied via IR spectroscopy. It is shown that surface hydroxyl groups of...     

Cooperative photoproduction of Xe2+Cl− in liquid Cl2/Xe solutions: Stimulated emission and gain measurements

Cooperative photogeneration of Xe₂⁺Cl⁻ can be accomplished by near UV laser excitation of Cl₂/Xe solutions with a high quantum efficiency. Gain measurements on the Xe₂⁺Cl⁻ (4²Γ) transition are reported. The liquid phase rare gas halides should be regarded as a family of ideal “dye” lasers.     

Densely Packed CO2 Aids Charge,Spin, and Lattice Ordering Partially Fluctuated in a Porous Metal–Organic Framework Magnet

Partial charge fluctuations in the charge-ordered state of a material, often triggered by structural disorders and/or defects, can significantly alter its physical characteristics, such as magnetic long-range ordering. However, it is difficult to post-chemically fix such accidental partial fluctuations to reconstruct a uniform charge-ordered state. Herein, we report CO₂-aided charge ordering demonstrated in a CO₂-post-captured layered magnet, [{Ru₂(o-ClPhCO₂)₄}₂{TCNQ(OMe)₂}] ⋅ CO₂ ( 1⊃CO₂ ; o-ClPhCO₂⁻=ortho-chlorobenzoate; TNCQ(OMe)₂=2,5-dimethoxy-7,7,8,8-tetracyanoquinodimethane). Pristine porous layered magnet 1 had a partially charge-fluctuated ordered state, which provided ferrimagnetic ordering at T_C=65 K. Upon loading CO₂, 1 adsorbed one mole of CO₂, forming 1⊃CO₂ , and raising T_C to 100 K. This was because of the vanishing charge fluctuations without significantly changing the framework structure. This research illustrates the post-accessible host–guest chemistry delicately combined with charge, spin, and lattice ordering in a spongy magnet. Furthermore, it highlights how this innovative approach opens up new possibilities for technology and nanoscale magnetism manipulation.     

The inflection point of the variation of interionic distance between Sm3+ and Cl− in a methanol and water mixture

The stability constants, β₁, of the monochloride complex of Sm(III) have been determined in mixed system of methanol and water at 1.00 mol dm⁻³ ionic strength using a solvent extraction technique. The values of β₁ increase with an increase in the mole fraction of methanol (X _s ) in the mixed solvent system when 0≤X _s ≤0.351. The interionic distance of Sm³⁺−Cl⁻ (d _Sm−Cl) in the mixed solvent system was estimated by applying the Gibb's free energy derived from β₁ to a Born-type equation. It was determined that an inflection point of the variation in the estimatedd _Sm−Cl againstX _s was present in the vicinity ofX _s =0.054. The inflection point ofd _Sm−Cl shows a value ofX _s between those ofd _Eu−Cl andd _Nd−Cl previously obtained by us.     

Synthesis and structure of a new compound (NH4)3[{Ta2(NH)3Cl6}Cl], with a novel imido-bridged chain: 1∞[Ta2(NH)3Cl6]2−

A new imido-bridged tantalum compound, (NH₄)₃[{Ta₂(NH)₃Cl₆}Cl], was synthesized from the mixture of TaCl₅, NaNH₂ and NH₄Cl (excess) in a vacuum sealed silica tube at 350–400 °C. Single crystal X-ray diffraction results for the title compound detailed in the orthorhombic space group Cmcm (No. 63); Z=4, a=10.1601(6) Å; b=19.8834(13) Å; and c=7.4362(4) Å. The structure consists of imido-bridged one-dimensional chains with composition [Ta₂(NH)₃Cl₆]²⁻ and running along c. These chains are separated by ammonium and chloride ions. In the present study, NH₄Cl was used to facilitate relatively smooth reaction between TaCl₅ and NaNH₂, which otherwise leads to an exothermic, self-propagating reaction.     

Thermodynamic quantities for the interaction of Cl− with Mg2+, Ca2+ and H+ in aqueous solution from 250 to 325°C

The aqueous reactions, Mg²⁺+Cl^–=MgCl⁺, Ca²⁺+Cl^–=CaCl⁺, and H⁺ +Cl^–=HCl(aq), were studied as a function of ionic strength at 250, 275, 300, and 325°C using a flow calorimetric technique. The logK, H, S and C_p values were determined from the fits of the calculated and experimental heast. The data were reduced assuming a known functionality of the activity coefficient. Hence, the logK, H, S and C_p values determined in this study are dependent on the activity coefficient model used. These thermodynamic values were compared with literature results. The logK values for the formation of MgCl⁺ agree reasonably well with those reported in the literature. The logK values for CaCl⁺ formation agree reasonably well with those reported in the literature at 300 and 325°C. At lower temperatures, the agreement is poorer. The logK values for the formation of HCl(aq) are generally lower than those reported in the literature. The logK, H, S and C_p values for all three ion association reactions are positive and increase with temperature over the temperature range studied. These values are the first determined calorimetrically for the formation of MgCl⁺ and CaCl⁺ in the temperature range 275–325°C.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.     

Electron doping versus antisite defects: Structural and magnetic properties of Sr2−xLaxCrMoO6 and Sr2−xLaxCr1+x/2Mo1−x/2O6 perovskites

This study reports the synthesis, structure and magnetic properties of Sr_2?xLa_xCrMoO₆ and Sr_2?xLa_xCr_1+x/2Mo_1?x/2O₆ samples. Although both series exhibit similar crystal structures, Sr_2?xLa_xCrMoO₆ samples present an effective electron doping revealed by a significant expansion of the unit cell with increasing x. In Sr_2?xLa_xCr_1+x/2Mo_1?x/2O₆ samples instead, the Cr-excess leads to a non electron doped system. Both series show a large amount of antisite defects whose number increases as La-content increases. Neutron diffraction patterns reveal the existence of long-range magnetic ordering for all samples but the magnetic peaks are very broad for Sr₂CrMoO₆ indicating a short coherence length of the magnetic ordering. This coherence length is increased upon replacing Sr by La. In both systems there is a clear increase of the magnetic transition temperature with increasing the La-content. The samples show ferromagnetic contributions at low temperature as deduced from the magnetic hysteresis loops typical of hard ferromagnetic materials. However, magnetic saturation is not achieved even at 5 T and the magnetic moment at this field is small. The ac magnetic susceptibility reveals the existence of several anomalies suggesting that these compounds are magnetically inhomogeneous. This is probably due to the presence of the large amount of structural defects not homogenously distributed.     

Reversible Transformation between a [PdL2]2+ “Figure-of-Eight” Complex and a [Pd2L2]4+ Dimer: Switching On and Off Self-Recognition

Structural changes to metallosupramolecular assemblies resulting in the release or uptake of guests are currently well established, whereas transformations turning on and off specific self-recognition are far less developed. We report a novel ligand (2,6-bis(1-(3-pyridin-4-yl)phenyl-1H-1,2,3-triazol-4-yl)pyridine) possessing a tridentate central metal-binding site flanked by two pendant pyridyl arms. In a 2:1 ratio with Pd^II metal ions, a spiro-type [PdL₂]²⁺ “Figure-of-eight” complex forms with the central tridentate binding pocket unoccupied. The introduction of an additional one equivalent of Pd^II metal ion results in the conversion to a dimeric [Pd₂L₂]⁴⁺ molecule with the tridentate pocket occupied. There is site-specific self-recognition between dimers in solution with strong NOE peaks between adjacent molecules. The self-recognition between dimers can be turned off in two ways: firstly, adding another equivalent of Pd^II metal ion brings about binding to the previously uncoordinated pyridyl arms that are key to the self-recognition event, and; secondly, addition of sufficient ligand to return the stoichiometry to 2:1 regenerates the [PdL₂]²⁺ complex. Hence, the self-recognition event can be turned on or off through simple variation of L:Pd^II stoichiometry.     

Vapor phase methylation of pyridine with CO?H2 and CO2?H2 over a Ni catalyst

Pyridine was methylated selectively to 2-picoline with CO−H₂ and with CO₂−H₂ over a Ni catalyst. 2,6-lutidine was producedvia the methylation of 2-picoline.     

Rapid,Selective Extraction of Silver from Complex Water Matrices with a Metal–Organic Framework/Oligomer Composite Constructed via Supercritical CO2

Every year vast quantities of silver are lost in various waste streams; this, combined with its limited, diminishing supply and rising demand, makes silver recovery of increasing importance. Thus, herein, we report a controllable, green process to produce a host of highly porous metal–organic framework (MOF)/oligomer composites using supercritical carbon dioxide (ScCO₂) as a medium. One resulting composite, referred to as MIL-127/Poly-o-phenylenediamine (PoPD), has an excellent Ag⁺ adsorption capacity, removal efficiency (>99 %) and provides rapid Ag⁺ extraction in as little as 5 min from complex liquid matrices. Notably, the composite can also reduce sliver concentrations below the levels (<0.1 ppm) established by the United States Environmental Protection Agency. Using theoretical simulations, we find that there are spatially ordered polymeric units inside the MOF that promote the complexation of Ag⁺ over other common competing ions. Moreover, the oligomer is able to reduce silver to its metallic state, also providing antibacterial properties.     

Dynamical competition between reactive and reactive detachment channels in X− + H2 colliding systems (X = Cl,Br, I)

Two reactive processes are observed: X⁻ + H₂ → XH + H⁻ (R) and X⁻ + H₂ → XH + H + e⁻ (RD). The angular and energy distributions of the molecular XH products are measured at collision energies varying from 5 to 10 eV center of mass. These distributions obey identical rules in the three systems: (a) XH molecules formed by both R and RD processes are scattered at the same c.m. angle, respectively 55° ±10 for ClH, 80° ±20 for BrH and 90° ±20 for IH. (b) The rovibrational energy of the XH molecules, when formed by R processes, is limited to a small amount: ⩽ 2 eV for ClH, ⩽ 1.5 eV for BrH, ⩽ 1 eV for IH, whereas when formed by RD it extends to the highest amount available from the collision energy, up to the dissociation limit. The RD process is not observed experimentally in the I⁻/H₂ system. This dynamical behaviour is fully understood in terms of non-adiabatic interaction between the two lowest [XH₂]⁻ ionic surfaces, but the reason of the angular anisotropy is still not well understood.     

Hydrothermal Synthesis and Crystal Structure of a Novel Selenite-chloride：[Cd4（SeO3）2Cl4（H2O）]n with a Three-dimensional Framework

A novel three-dimensional(3-D) compound [Cd4(SeO3)2Cl4(H2O)]n(1) was prepared from a hydrothermal reaction and structurally characterized.Compound 1 crystallizes in the space group Fmmm of the orthorhombic system with eight formula units in a cell:a = 15.5165(4),b = 17.5090(9),c = 7.3318(5) ,V = 1991.9(2) 3,Cd4Cl4H2O7Se2,Mr = 863.38,Dc = 5.758 g/cm3,S = 1.075,μ(MoKα) = 16.820 mm-1,F(000) = 3088,R = 0.0427 and wR = 0.1220.Compound 1 features a 3-D structure with the cadmium atoms having two different coordination environments,i.e.,six-and eight-coordination geometries.Two different chain-like structures of cadmium-oxo polyhedra are interconnect to each other to give a 2-D layer of [Cd4(SeO3)2(H2O)]n4n+.Between the [Cd4(SeO3)2(H2O)]n4n+ layers is a novel chloride layer.A 3-D framework is constructed from these [Cd4(SeO3)2(H2O)]n4n+ layers linked by the chloride layers.     

CO2/H2S corrosion behavior of tubular steel SM 80SS in Cl−-containing solution in the absence or presence of Ca2+ and Mg2+

CO₂/H₂S corrosion behavior of tubular steel SM 80SS have been investigated utilizing electrochemical measurement technology, weight loss test, scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that temperature increased the corrosion rate and changed the corrosion mechanism of tubular steel SM 80SS. Cl^? quickened the anodic dissolution and increased the corrosion rate of tubular steel SM 80SS. Furthermore, the addition of Ca²⁺ and Mg²⁺ resulted in the corrosion products changing from crystalline FeCO₃ to amorphous Fe(Ca,Mg)(CO₃)₂ and serious corrosion under scale of tubular steel SM 80SS.     

A Trinuclear Cobalt–Organic Framework: Solvatochromic Sensor towards CH2Cl2, and its Derivative as an Anode of Lithium-Ion Batteries with High Performance

Here, a porous cobalt–organic framework with pillared layer structures, namely [Co₃OBA₃PTD(H₂O)₂ ⋅ 2 DMA ⋅ H₂O]_n ( 1 , H₂OBA=4,4′-oxybis(benzoic acid); PTD=6-(pyridin-4-yl)-1,3,5-triazine-2,4-diamine), was fabricated by using cobalt trinuclear nodes, low-cost carboxylic linker, and accessible nitrogen heterocyclic ligands. This compound exhibited a highly efficient solvatochromism towards CH₂Cl₂ within one minute and can be used 200 times at least. The corresponding dropper detector was assembled as a practical sensor. Meanwhile, the porous Co₃O₄ was obtained by a simple but effective annealing treatment. Electrochemical measurements confirm that this Co₃O₄ material derived from compound 1 shows high and stable lithium storage capabilities (1081.75 mA h g⁻¹ at 200 mA g⁻¹ after 115 cycles) and excellent rate properties.     

Strategic Substitution of −OH/−NR2 (R=Et,Me) Imparts Colorimetric Switching between F− and Hg2+ by Salicyaldehyde/Benzaldehyde-Quinoxaline Conjugates

We herein report two salicyaldehyde-quinoxaline ( HQS and HQSN ) conjugates and a benzaldehyde-quinoxaline ( QBN ) conjugate to fabricate selective chemosensors for F⁻ and Hg²⁺ in the micromolar range. This work demonstrates how sensing outcomes are affected by modulating proton acidity by introducing an electron donating group, −NEt₂, in the probe backbone. Interestingly, the un-substituted probe HQS can selectively detect F⁻, whereas HQSN and QBN are selective for Hg²⁺. In order to gain insights into the mechanism of sensing, geometry optimizations have been carried out on QS⁽⁻¹⁾ , QS⁽⁻¹⁾⋅⋅⋅HF , QSN⁽⁻¹⁾ and QSN⁽⁻¹⁾⋅⋅⋅HF and the experimental data are validated in terms of free energy and pK_a values. Detailed DFT and TD-DFT analyses provide ample support towards the mechanism of sensing of the analytes.     

Volumetric properties of a stoichiometric mixture of K+ and Br− ions in H/D isotope-substituted aqueous-methanolic solutions between 278.15 and 318.15 K: II. H2O-CD3OH-KBr and D2O-CH3OD-KBr systems

The magnetoflotation densities of potassium bromide solutions in H₂O-CD₃OH and D₂O-CH₃OD mixtures are measured using, with an error of at most ±(1.0 × 10^?5) g/cm³ for methanol mole fractions x ₂ of 0.06, 0.1, 0.3, or 0.6; and for the potassium bromide mole fractions up to about 2.65 × 10^?2 at 278.15–318.15 K in 10-K steps. The limiting partial molar volumes $\bar V_3^\infty $ of a stoichiometric [K⁺ + Br^?] mixture and the corresponding H/D isotope effects are calculated. The key role in the volumetric effects of salt solvation is played by the interactions between bromide ions and molecules of the mixed solvent, resulting in hydrogen-type bonding.     

Synthesis and Structural Characterization of One New Polyoxotungstate Connected via Potassium Cations with a Three-dimensional Framework: H6Na2K4(H2W12O42)Cl2·14H2O

One new polyoxotungstate complex H6Na2K4(H2W12O42)Cl2·14H2O 1 has been prepared in the beaker solution and characterized by elemental analysis and IR spectroscopy. Crystal data: H36Cl2K4W12Na2O56, Mr = 3411.77, monoclinic, space group P21/c, a = 11.5734(16), b = 14.3136(19), c = 15.459(2)(A), β = 105.601(2)°, V = 2466.5(6)(A)3, Z = 2, Dc = 4.594 g/cm3, F(000) = 3008, μ = 28.447 mm-1, R = 0.0574 and wR = 0.1239 (Ⅰ＞ 2σ(Ⅰ)). Single-crystal X-ray diffraction analysis results reveal that a three-dimensional architecture in the title compound is constructed from the H2W12O4210- units linked by potassium.