Spectroelectrochemical studies of magnesium deposition by in situ FTIR spectroscopy

Magnesium can be reversibly deposited electrochemically from solutions of ethereal solvents, with Grignard reagents (RMgX) or complexes of Mg(AX_3−nR_n+1)₂ stoichiometry as the electrolytes (A=Al, B; X=Cl, Br; R=alkyl or aryl groups). These processes are far from being simple reactions of the Mg/Mg⁺⁺ couple, since the above electrolytes in solutions have complicated structures in which the ether molecules play an important stabilization role. In addition, Mg deposition processes in all of the above solutions are accompanied by adsorption phenomena. The surface chemistry of magnesium electrodes was studied in situ by FTIR spectroscopy, using an internal reflectance mode. The electrolyte solutions studied included tetrahydrofuran (THF) solutions of the RMgX electrolytes (R=butyl, ethyl, methyl benzyl, and X=Cl, Br); Mg(AlCl₂BuEt)₂; Mg(AlCl₃Bu)₂ and Mg(BPh₂Bu₂); Bu, Et, Ph=butyl, ethyl and phenyl groups, respectively. It was clear from these studies that Mg electrodes do not develop stable passivation in these solutions (i.e. formation of surface films). The nature of the adsorbed species in the above systems is discussed, based on the spectral results.     

Thermodynamic equilibrium analyses of the uptake of aromatic compounds from an aqueous solution by magnesium–aluminum (Mg–Al) layered double hydroxide intercalated with 1-naphthol-3,8-disulfonate

Magnesium–aluminum layered double hydroxide (Mg–Al LDH) intercalated with 1-naphthol-3,8-disulfonate (1-N-3,8-DS²⁻) was prepared by coprecipitation. Thermodynamically, the prepared Mg–Al LDH showed greater preferential uptake of 1,3-dinitrobenzene (DNB) than of 1,2-dimethoxybenzene (DMB). This preferential uptake of aromatic compounds, which is adequately expressed by the Dubinin–Radushkevich adsorption isotherm, was attributed to the π–π stacking interactions between the benzene ring of the aromatic compounds and the naphthalene core of 1-N-3,8-DS²⁻ intercalated in the interlayer spaces of Mg–Al LDH. Negative values of ΔG for DNB and DMB indicate that the adsorption process is spontaneous at all temperatures. The value of ΔS for DNB was much lower than that for DMB. This implies that DNB was far more strongly adsorbed to 1-N-3,8-DS²⁻ than was DMB, resulting in a lower degree of freedom for and higher uptake of DNB than those in the case DMB. The absolute values of |ΔH| for DNB and DMB were less than 20 kJ mol⁻¹, indicating that the uptake of DNB or DMB by 1-N-3,8-DS·Mg–Al LDH can be considered a physical adsorption process caused by π–π stacking interactions.     

Hydrothermal synthesis of nanotubular Mg-Fe hydrosilicate

Magnesium iron hydrosilicate nanotubes with a chrysotile ((Mg,Fe)₃Si₂O₅(OH)₄) structure have been synthesized hydrothermally at t = 250–450°C and p = 30–100 MPa. In the hydrothermal synthesis of (Mg,Fe)₃Si₂O₅(OH)₄ chrysotile, part of the Fe²⁺ ions oxidize to Fe³⁺ and are incorporated into the octahedron and tetrahedron layers of the chrysotile structure. The limiting iron content of chrysotile has been determined up to which cylindrically rolled layers can form to yield nanotubes. The hydrothermal treatment of precursors richer in FeO yields platelike hydrosilicates. The iron ions present in the starting components affect the synthesis parameters, morphology, size, optical properties, and thermal stability of the nanotubes.     

Magnesiumphthalocyanine: Darstellung und Eigenschaften von Halogenophthalocyaninatomagnesat, [Mg(X)Pc2−]− (X = F,Cl, Br); Kristallstruktur von Bis(triphenylphosphin)iminiumchloro(phthalocyaninato)magnesat-Aceton-Solvat

Magnesium Phthalocyanines: Synthesis and Properties of Halophthalocyaninatomagnesate, [Mg(X)Pc^2?]^? (X = F, Cl, Br); Crystal Structure of Bis(triphenylphosphine)iminiumchloro-(phthalocyaninato)magnesate Acetone Solvate Magnesium phthalocyanine reacts with excess tetra(n-butyl)ammonium- or bis(triphenylphosphine)iminiumhalide ((ⁿBu₄N)X or (PNP)X; X = F, Cl, Br) yielding halophthalocyaninatomagnesate ([Mg(X)Pc^2?]^?; X = F, Cl, Br), which crystallizes in part as a scarcely soluble (ⁿBu₄N) or (PNP) complex-salt. Single-crystal X-ray diffraction analysis of ^b(PNP)[Mg(Cl)Pc^2?] · CH₃COCH₃ reveals that the Mg atom has a tetragonal pyramidal coordination geometry with the Mg atom displaced out of the center (Ct) of the inner nitrogen atoms (N_iso) of the nonplanar Pc ligand toward the Cl atom (d(Mg? Ct) = 0.572(3) Å; d(Mg? Cl) = 2.367(2) Å). The average Mg? N_iso distance is 2.058 Å. Pairs of partially overlapping anions are present. The cation adopts a bent conformation (^b(PNP)⁺: d(P1? N(K)) = 1.568(3) Å; d(P2? N(K)) = 1.587(3) Å; ?(P1? N(K)? P2) = 141.3(2)°). Electrochemical and spectroscopic properties are discussed.     

Magnesium(I) Halide versus Magnesium Metal: Differences in Reaction Energy and Reactivity Monitored in Reduction Processes of P−Cl Bonds

Magnesium(I) halides (Mg^IX; X=Cl, Br, I), as high temperature molecules, are trapped and finally stored at ?80 °C in toluene/donor solutions. These solutions provide insights into the fundamental mechanism of reduction reactions using activated magnesium metal as a prototype for every base metal. The most important example of such a reaction is the preparation of Grignard reagents (RMgX). The details of this highly complex mechanism especially of intermediates between Mg metal and Mg^II (RMgX) remain unknown until today. The same is true for the reaction of bulk magnesium with Group 15 halide compounds that give biradicaloid species. We investigate the reduction of P?Cl bonds with solutions of [Mg^IBr(NⁿBu₃)]₂ ( 1 ). The phosphanes [ClP(μ‐NTer)]₂ ( 2 ) and (Me₃Si)₂N‐PCl₂ ( 3 ), were chosen as they had successfully been reduced by Mg metal before. Furthermore, reactions of both 1 and Mg metal are compared with an Mg^I chelate complex L¹Mg?MgL¹ containing a strong Mg?Mg σ‐bond.     

Synthesis,Crystal Structure,and Electrochemical Properties of a Simple Magnesium Electrolyte for Magnesium/Sulfur Batteries

Most simple magnesium salts tend to passivate the Mg metal surface too quickly to function as electrolytes for Mg batteries. In the present work, an electroactive salt [Mg(THF)₆][AlCl₄]₂ was synthesized and structurally characterized. The Mg electrolyte based on this simple mononuclear salt showed a high Mg cycling efficiency, good anodic stability (2.5 V vs. Mg), and high ionic conductivity (8.5 mS cm^?1). Magnesium/sulfur cells employing the as‐prepared electrolyte exhibited good cycling performance over 20 cycles in the range of 0.3–2.6 V, thus indicating an electrochemically reversible conversion of S to MgS without severe passivation of the Mg metal electrode surface.     

Synthesis,Crystal Structure,and Electrochemical Properties of a Simple Magnesium Electrolyte for Magnesium/Sulfur Batteries

Most simple magnesium salts tend to passivate the Mg metal surface too quickly to function as electrolytes for Mg batteries. In the present work, an electroactive salt [Mg(THF)₆][AlCl₄]₂ was synthesized and structurally characterized. The Mg electrolyte based on this simple mononuclear salt showed a high Mg cycling efficiency, good anodic stability (2.5 V vs. Mg), and high ionic conductivity (8.5 mS cm⁻¹). Magnesium/sulfur cells employing the as‐prepared electrolyte exhibited good cycling performance over 20 cycles in the range of 0.3–2.6 V, thus indicating an electrochemically reversible conversion of S to MgS without severe passivation of the Mg metal electrode surface.     

Contribution to the atomic absorption spectrophotometry of magnesium in the air-acetylene flame

Summary Non-sufficient attention seems to have been paid to the influence of various ions on the atomic absorption spectrophotometric determination of magnesium. SiO₃ ²⁺, Al³⁺, Be²⁺, Zr(IV), Ti(IV) decrease remarkably the Mg absorbance in air-acetylene flames, but the most interesting positive or negative effects on the absorbance of magnesium are exhibited in ternary systems of ions. 5-Sulphosalicylic acid protects magnesium in the presence of the above mentioned elements in binary or ternary ion systems and makes the atomic absorption spectrophotometric determination of magnesium possible in the presence of these ions.

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Zur atomabsorptionsspektrophotometrischen Bestimmung von Magnesium in der Luft-Acetylen-Flamme

Zusammenfassung Den verschiedenen Beeinflussungen durch Kationen und Anionen bei der atomabsorptionsspektrophotometrischen Bestimmung von Magnesium wurde bisher nur unzureichende Aufmerksamkeit gewidmet. Vor allem SiO₃ ^2–, Al³⁺, Be²⁺, Zr(IV), Ti(IV) üben einen merklichen negativen Einfluß auf die Absorption von Magnesium in der Acetylen-Luft-Flamme aus. Von besonderer Bedeutung sind verstärkte negative bzw. positive Einflüsse in ternären Ionensystemen, die die Resultate stark beeinträchtigen können. 5-Sulfosalicylsäure eignet sich im allgemeinen gut zur Aufhebung des störenden Ioneneinflusses bei der Bestimmung von Magnesium neben den oben genannten Elementen in binären oder ternären Systemen in Acetylen-Luft-Flammen.

     

AMoO4 (A = Mg,Ni) molybdates: Phase stabilities,electronic structures and chemical bonding properties from first principles

Stability of different phases of AMoO₄ (A = Mg, Ni) molybdates versus A–O bonding and the corresponding electronic structures are examined from first principles. The energy-volume equations of state for three forms (β, α, ω), characterized by decreasing volumes in the sequence of Mg and Ni molybdates are established. While NiMoO₄ is energy stabilized in the sequence β → α → ω, an opposite behavior is identified for the Mg molybdate. Charge analysis characterizing ionic Mg²⁺ versus covalent Ni^+1.2 behaviors can explain the trend. Electronic band structure also shows large differences: MgMoO₄ is insulating with a ～2 eV band gap while in a magnetic state, NiMoO₄ is a small gap (～0.2 eV) semi-conductor. Chemical bonding properties show weak Mg and strong Ni bonding with oxygen, while identifying the Mo–O interaction as prevailing.     

Nitrogen Plasma Enhanced Low Temperature Atomic Layer Deposition of Magnesium Phosphorus Oxynitride (MgPON) Solid-State Electrolytes

Solid-state batteries (SSBs) that use solid electrolytes instead of flammable liquid electrolytes have the potential to generate higher specific capacity and offer better safety. Magnesium (Mg) based SSBs with Mg metal anodes are considered to be one of the most promising energy storage candidates, because it gives high theoretical volumetric capacities of 3830 mAh cm⁻³. Here, we demonstrate an atomic layer deposition (ALD) process with a double nitrogen plasma process that successfully produces nitrogen-incorporated magnesium phosphorus oxynitride (MgPON) solid-state electrolyte (SSE) thin films at a low deposition temperature of 125 °C. The ALD MgPON SSEs exhibit an ionic conductivity of 0.36 and 1.2 μS cm⁻¹ at 450 and 500 °C, respectively. The proposed ALD strategy shows the ability of conformal deposition nitrogen-doped SSEs on pattered substrates and is attractive for using nitride ion-conducing films as protective or wetting interlayers in solid-state Mg and Li batteries.     

Isotopic Exchange in Porous and Dense Magnesium Borohydride

Magnesium borohydride (Mg(BH₄)₂) is one of the most promising complex hydrides presently studied for energy‐related applications. Many of its properties depend on the stability of the BH₄^? anion. The BH₄^? stability was investigated with respect to H→D exchange. In situ Raman measurements on high‐surface‐area porous Mg(BH₄)₂ in 0.3 MPa D₂ have shown that the isotopic exchange at appreciable rates occurs already at 373 K. This is the lowest exchange temperature observed in stable borohydrides. Gas–solid isotopic exchange follows the BH₄^?+D^.→BH₃D^?+H^. mechanism at least at the initial reaction steps. Ex situ deuteration of porous Mg(BH₄)₂ and its dense‐phase polymorph indicates that the intrinsic porosity of the hydride is the key behind the high isotopic exchange rates. It implies that the solid‐state H(D) diffusion is considerably slower than the gas–solid H→D exchange reaction at the surface and it is a rate‐limiting steps for hydrogen desorption and absorption in Mg(BH₄)_2.     

Cathode Electrolyte Interphase (CEI) Endows Mo6S8 with Fast Interfacial Magnesium-Ion Transfer Kinetics

Magnesium (Mg) metal secondary batteries have attracted much attention for their high safety and high energy density characteristics. However, the significant issues of the cathode/electrolyte interphase (CEI) in Mg batteries are still being ignored. In this work, a significant CEI layer on the typical Mo₆S₈ cathode surface has been unprecedentedly constructed through the oxidation of the chloride-free magnesium tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)₄]₂) salt under a proper charge cut-off voltage condition. The CEI has been identified to contain B_xO_y effective species originating from the oxidation of [B(hfip)₄]⁻ anion. It is confirmed that the B_xO_y species is beneficial to the desolvation of solvated Mg²⁺, speeding up the interfacial Mg²⁺ transfer kinetics, thereby improving the Mg²⁺-storage capability of Mo₆S₈ host. The firstly reported CEI in Mg batteries will give deeper insights into the interface issues in multivalent electrochemical systems.     

Unsupported Mg–Alkene Bonding

The first intermolecular early main group metal–alkene complexes were isolated. This was enabled by using highly Lewis acidic Mg centers in the Lewis base-free cations (^MeBDI)Mg⁺ and (^tBuBDI)Mg⁺ with B(C₆F₅)₄⁻ counterions (^MeBDI=CH[C(CH₃)N(DIPP)]₂, ^tBuBDI=CH[C(tBu)N(DIPP)]₂, DIPP=2,6-diisopropylphenyl). Coordination complexes with various mono- and bis-alkene ligands, typically used in transition metal chemistry, were structurally characterized for 1,3-divinyltetramethyldisiloxane, 1,5-cyclooctadiene, cyclooctene, 1,3,5-cycloheptatriene, 2,3-dimethylbuta-1,3-diene, and 2-ethyl-1-butene. In all cases, asymmetric Mg–alkene bonding with a short and a long Mg−C bond is observed. This asymmetry is most extreme for Mg–(H₂C=CEt₂) bonding. In bromobenzene solution, the Mg–alkene complexes are either dissociated or in a dissociation equilibrium. A DFT study and AIM analysis showed that the C=C bonds hardly change on coordination and there is very little alkene→Mg electron transfer. The Mg–alkene bonds are mainly electrostatic and should be described as Mg²⁺ ion-induced dipole interactions.     

Accumulation of selected metals in the fruits of medicinal plants grown in urban environment of Islamabad,Pakistan

The present study is based on the measurement of selected metals (Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Pb, Sr and Zn) in the fruits of eight medicinal plants (Carrisa opeca, Phyllanthus emblica, Solanum nigrum, Zizyphus nummularia, Zizyphus mauritiana, Physalis minima, Opuntia dillenii and Phoenix dactylifera) and relevant soil samples by atomic absorption spectrometry. Highest average concentrations of Cu (14.4 mg/kg), Cr (19.0 mg/kg), and Zn (125 mg/kg) were found in the fruits of P. minima, C. opeca and Z. nummularia, respectively, while O. dillenii showed the elevated mean levels of Cd (3.49 mg/kg), Sr (61.4 mg/kg), Mg (0.21%), Ca (6.62%) and Mn (44.6 mg/kg). However, highest average levels of Pb (41.7 mg/kg) and Co (38.4 mg/kg) were found in Z. mauritiana. Overall, most of the fruit samples showed higher contributions of Ca and Mg, followed by Fe, Zn, Co and Pb. In the case of soil samples, highest concentration was observed for Ca, followed by Fe, Mg, Mn and Sr, while lowest concentration was shown by Cd. Bioaccumulation factors exhibited significantly higher accumulation of Co (0.813–1.829) and Pb (0.060–2.350) from the soil to the fruits. Principal component analysis revealed significant anthropogenic contributions of Pb, Fe and Co in the fruit samples. Contamination factors and enrichment factors of Cd and Pb in the soil indicated very high contamination and extreme enrichment of these metals.     

Strukturen von polaren Magnesiumorganylen: Synthese und Struktur von Basen‐Addukten des Bis(cyclopentadienyl)magnesiums

Structures of Polar Magnesium Organyls: Synthesis and Structure of Base Adducts of Bis(cyclopentadienyl)magnesium Eight donor‐acceptor complexes of bis(cyclopentadienyl)magnesium ( 1 ) with N‐ and O‐donor Lewis bases have been synthesized and characterized by X‐ray structure analysis. With acetonitrile, dimethoxyethane, diethyleneglycoldimethylether, dioxane, and tetramethylethylenediamine simple 1:1 adducts are formed ( 2 – 6 ). In some cases a change of the hapticity of one cyclopentadienylring from η⁵ to η² or η¹ is observed ( 4 – 6 ). In the adduct with pentamethyldiethylenetriamine ( 7 ) one C₅H₅‐ring is removed from the magnesium atom forming the cation [Mg(C₅H₅)(PMDTA)]⁺ and an uncoordinated five‐ring anion. With the crown ether 15‐crown‐5 the two ionic Mg compounds 8 and 9 are formed which have a [Mg(15‐crown‐5)L₂]²⁺‐cation [L = pyridine, THF] and two uncoordinated cyclopentadienyl anions. Cyclopentadienyl‐methyl‐magnesium reacts with 15‐crown‐5 to the salt [Mg(CH₃)(15‐crown‐5)]⁺ C₅H₅^? ( 10 ) which has also a free cyclopentadienyl anion.     

Evaluation of droplet digital PCR for characterizing plasmid reference material used for quantifying ammonia oxidizers and denitrifiers

DNA reference materials of certified value have a critical function in many analytical processes of DNA measurement. Quantification of amoA genes in ammonia oxidizing bacteria (AOB) and archaea (AOA), and of nirS and nosZ genes in the denitrifiers is very important for determining their distribution and abundance in the natural environment. A plasmid reference material containing nirS, nosZ, amoA-AOB, and amoA-AOA is developed to provide a DNA standard with copy number concentration for ensuring comparability and reliability of quantification of these genes. Droplet digital PCR (ddPCR) was evaluated for characterization of the plasmid reference material. The result revealed that restriction endonuclease digestion of plasmids can improve amplification efficiency and minimize the measurement bias of ddPCR. Compared with the conformation of the plasmid, the size of the DNA fragment containing the target sequence and the location of the restriction site relative to the target sequence are not significant factors affecting plasmid quantification by ddPCR. Liquid chromatography–isotope dilution mass spectrometry (LC–IDMS) was used to provide independent data for quantifying the plasmid reference material. The copy number concentration of the digested plasmid determined by ddPCR agreed well with that determined by LC–IDMS, improving both the accuracy and reliability of the plasmid reference material. The reference value, with its expanded uncertainty (k?=?2), of the plasmid reference material was determined to be (5.19?±?0.41)?×?10⁹ copies μL^?1 by averaging the results of two independent measurements. Consideration of the factors revealed in this study can improve the reliability and accuracy of ddPCR; thus, this method has the potential to accurately quantify DNA reference materials.     

Separation of alkaline earth elements by cation-exchange chromatography in ammonium malonate media

Be(II), Mg(II), Ca(II), Sr(II) and Ba(II) can be separated by elution from a cation-exchange column in the ammonium form with increasing concentrations of ammonium malonate. A typical elution sequence for a 60-ml column (volume in H⁺-form) of AG₅₀-X8 resin is: 200 ml of 0.20 N ammonium malonate plus 0.10 N malonic acid for Be(II); 300 ml of 0.50 N, 450 ml of 0.70 N, 350 ml of 1.10 N ammonium malonate for Mg(II), Ca(II) and Sr(II), respectively, and 200 ml of 3.0 N nitric acid for Ba(II). Separations are sharp and quantitative for element pairs in weight ratios from 1:1000 to 1000:1. Distribution coefficients, elution curves and quantitative separations are presented.     

Nuclear spin catalysis in living nature

Experiments with cells enriched in stable magnesium isotopes, magnetic ²⁵Mg or nonmagnetic ²⁴Mg and ²⁶Mg, are carried out. It is revealed that adaptation of bacteria E. coli to the growth media enriched in magnetic ²⁵Mg proceeds faster as compared to the growth media enriched in nonmagnetic magnesium isotopes. In experiments with another commonly accepted cell model, S. cerevisiae yeast, it is revealed that the rate constant of postradiation recovery of the cells after UV irradiation is two times higher for cells enriched in ²⁵Mg than for cells enriched in the nonmagnetic isotope. In collaboration with Ukrainian colleagues from the Palladin Institute of Biochemistry, the effects of different isotopes of magnesium on ATPase activity of myosin isolated from myometrium are studied. It is found that the rate of the enzymatic hydrolysis of ATP for ²⁵Mg is 2.0–2.5 times higher as compared to nonmagnetic isotopes ²⁴Mg and ²⁶Mg. Some possible mechanisms of magnetic isotope effects (nuclear spin catalysis) in biological objects are discussed.     

Syntheses and crystal structures of [Mg(HF)2](SbF6)2 and [Ca(HF)2](SbF6)2: new examples of HF acting as a ligand to metal centres

[Mg(HF)₂](SbF₆)₂ and [Ca(HF)₂](SbF₆)₂ monocrystals were grown from the corresponding hexafluoroantimonates(V) dissolved in anhydrous hydrogen fluoride. [Mg(HF)₂](SbF₆)₂ crystallizes in the space group Pnma (no. 62) with a=1249.1(4) pm, b=1230.2(4) pm, c=699.1(2) pm, V=1.0742(6) nm³, Z=4. Magnesium is octahedrally coordinated by six fluorine atoms from which two belong to two HF molecules. The structure can be represented by alternating rows of magnesium and antimony atoms running parallel to the c-axis. Magnesium atoms are connected by cis bridging Sb(2)F₆ units along the a-axis and by trans bridging Sb(1)F₆ units along the b-axis. In this way a three-dimensional network is formed.[Ca(HF)₂](SbF₆)₂ crystallizes in the space group P2₁/n (no. 14) with a=935.2(3) pm, b=1088.7(3) pm, c=1104.8(3) pm, β=106.697(5)°, V=1.0774(5) nm³, Z=4. The coordination sphere around the calcium atom consists of eight fluorine atoms which define the vertices of an Archimedean antiprism. The two HF molecules directly coordinate the calcium atom and their fluorine atoms are placed in the corners of different square faces of the Archimedean antiprism. The Ca-F(HF) distances are shorter than the Ca-F(Sb) distances. The Sb(1)F₆ and Sb(2)F₆ groups have four equatorial bridging fluorine atoms, while the Sb(3)F₆ groups have only two bridging trans F ligands. The Ca atoms in the [−1,0,1] plane are connected by equatorial F ligands of Sb(1)F₆ and Sb(2)F₆ units, forming a [Ca(SbF₆)⁺]_n layer. These layers are connected by trans bridging Sb(3)F₆ groups. HF molecules occupy the space between these layers and additionally contribute to the connection between the layers by hydrogen bonding.