Paramagnetic properties of triple molybdates CsNa<Subscript>5</Subscript>M<Subscript>3</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>6</Subscript> (M = Ni,Co, Mn)

The static magnetization of CsNa₅M₃(MoO₄)₆ single phase molybdates, where M = Co, Ni, and Mn, is measured at 4–300 K in magnetic fields of up to 20 kOe. It is shown that the materials are paramagnetic. Magnetization as a function of temperature is described using the Curie–Weiss law. The intrinsic magnetic moments of the phases are found to be 9.759 (Co), 6.958 (Ni), and 12.203 Bohr magnetons for manganese molybdates. It is concluded that the charge state of Co, Ni, and Mn cations in the compounds is +2.     

Charge distribution and mobility of lithium ions in Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> from <Superscript>6,7</Superscript>Li NMR data

A comparative analysis of ^6,7Li NMR spectra is performed for the samples of monoclinic lithium titanate obtained at different synthesis temperatures. In the ⁷Li NMR spectra three lines are found, which differ in quadrupole splitting frequencies v _Q and according to ab initio EFG calculations are assigned to three crystallographic sites of lithium: Li1 (v _Q ～ 27 kHz); Li2 (v _Q ～ 59 kHz); Li3 (v _Q ～ 6 kHz). The dynamics of lithium ions is studied in a wide temperature range from 300 K to 900 K. It is found that the narrowing of ⁷Li NMR spectra as a result of thermally activated diffusion of lithium ions in the low-temperature Li₂TiO₃ sample is observed at a higher temperature in comparison with a sample of high-temperature lithium titanate. Based on the analysis of ⁶Li NMR spectra it is assumed that there is mixed occupancy of lithium and titanium sites in the corresponding layers of the crystal structure of low-temperature lithium titanate, which hinders lithium ion transfer over regular crystallographic sites.     

LiMO<Subscript>2</Subscript>@Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript> positive-electrode material for high energy density lithium ion batteries

Li[Ni_1/3Co_1/3Mn_1/3]O₂ (NCM 111) is a promising alternative to LiCoO₂, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g^?1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO₂ (R-3m, M?=?Ni, Co) and a shell of Li₂MnO₃ (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li⁺/Ni²⁺ cation disorder and stronger M*–O (M*?=?Mn, Co, Ni) bonds than NCM 111. The core–shell material Li_1.15Na_0.5(Ni_1/3Co_1/3)_core(Mn_1/3)_shellO₂ can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g^?1 at 20 mA g^?1, and retains 90 % of its discharge capacity at 100 mA g^?1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.

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Graphical Abstract Average voltage vs. number of cycles for the core–shell and pristine materials at 20 mA g^?1 for 10 cycles followed by 90 cycles at 100 mA g^?1

     

Ion mobility and conductivity in the Li(NH<Subscript>3</Subscript>CH<Subscript>2</Subscript>COO)(NO<Subscript>3</Subscript>) compound

(⁷Li, ¹H) NMR and impedance spectroscopy methods are used to study the ion mobility and conductivity in a complex of the composition Li(NH₃CH₂COO)(NO₃) (I), which has a layered crystal structure. The character of ion motions in lithium and proton sublattices with temperature variation is considered; the types of motions and temperature ranges in which they occur are determined. It is found that above 350 K the dominant process in the lithium sublattice of the compound is Li⁺ ion diffusion. Possible migration paths of lithium ions in the lattice of the compound are analyzed. The specific conductivity of the compound is found to be 2.4×10^–6 S/cm at 393 K.     

<Superscript>1</Superscript>H and <Superscript>7</Superscript>Li NMR in defect cobaltite Li<Subscript>0.6</Subscript>CoO<Subscript>2</Subscript>

Within a temperature range of 120–330 K, ⁷Li NMR spectra in Li_0.6CoO₂ are obtained. It is shown that as the temperature increases, both smooth and stepwise variation of ⁷Li NMR contact shifts occurs. The observed effects are explained by the occupation of the excited levels of cobalt ions. The stepwise change of the resonance line width depending on the temperature is revealed. It is driven by the features of the diffusive motion of lithium ions. The calculation of the ¹H NMR line shape provides the determination of the ratio of one-, two-, and three-spin proton clusters in Li_0.6CoO₂·xH₂O.     

Synthesis,structures, and physicochemical properties of Sr<Subscript>2</Subscript>A<Superscript>II</Superscript>UO<Subscript>6</Subscript> (A<Superscript>II</Superscript> = Mg,Ca, Sr,Ba, Mn,Fe, Co,Ni, Zn,and Cd) compounds

Sr₂A^IIUO₆ (A^II = Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Zn, and Cd) compounds were synthesized by high-temperature reactions in the solid phase. The crystal structure (space group P2₁/n) was refined by the Rietveld method for Sr₂MgUO₆, (Sr_0.5Ba_0.5)₂SrUO₄, and Sr₂CdUO₆, which were synthesized for the first time. IR spectral characteristics were studied. The standard enthalpies of formation of the compounds were determined by reaction calorimetry.     

Electronic structure and quadrupole interactions in triple molybdates Li<Subscript>2</Subscript>M<Subscript>3</Subscript>Al(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript>, M = Cs,Rb

Within the density functional theory the electronic structure of triple molybdates Li₂M₃Al(MoO₄)₄, where M = Cs, Rb, is studied for the first time. It is found that all molybdates studied belong to wide band insulators with a band gap of ~4 eV. Quadrupole frequencies and asymmetry parameters of the electric field gradient near magnetic ⁷Li, ²⁷Al, ⁸⁷Rb, and ¹³³Cs nuclei are calculated and experimental NMR spectra are interpreted.     

Synthesis and characterization of new ammonium-containing niobium fluoro complexes of composition NH<Subscript>4</Subscript>NaNbF<Subscript>7</Subscript> and NH<Subscript>4</Subscript>MNbOF<Subscript>5</Subscript> (M = Li and Na)

Ammonium-containing mixed-alkali-metal fluoro complexes NH₄NaNbF₇ and NH₄MNbOF₅ (M = Li and Na) crystallizing in orthorhombic system were synthesized and characterized for the first time. Unit cell parameters for these complexes were determined. Their IR absorption spectra were measured and characterized in the range 4000-350 cm⁻¹.     

A comparative screening of the catalytic activity of nanocrystalline M<Superscript>II</Superscript>Zr<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>6</Subscript> ceramics in the one-pot synthesis of 1,6-diamino-4-aryl-2-oxo-1,2-dihydropyridine-3,5-dicarbonitrile derivatives

A four-component reaction of hydrazine hydrate, ethyl cyanoacetate, malononitrile, and aromatic aldehydes was achieved in the presence of nanocrystalline M^IIZr₄(PO₄)₆ ceramics (M^II: Mn, Fe, Co, Ni, Cu, Zn, Cd) as heterogeneous catalysts to produce N-amino-2-pyridones. The reactions were performed in the presence of different catalysts, and it is observed that CdZr₄(PO₄)₆ nanocrystallines are the best catalysts among those examined. Atom economy, excellent yields in short times, high catalytic activity, recycling of catalyst, and environmental benignity are some of the important features of this protocol.     

Hydride lithiation of spinels LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>

Undoped lithiation of stoichiometric spinel using lithium hydride LiH up to the composition Li_2.25Mn₂O₄ was performed. A homogeneous material with a given Li: Mn ratio was obtained by mechanochemical activation with sequential annealing of a LiMn₂O₄–LiH mixture in a high-purity argon atmosphere and then in air or oxygen at 373–553 K.     

Structure and lithium mobility of Li<Subscript>4</Subscript>Pt<Subscript>3</Subscript>Si

The lithium-rich silicide Li₄Pt₃Si was synthesised from the elements by high-temperature synthesis in a sealed niobium ampoule. Its structure was refined on the basis of single-crystal X-ray diffraction data: R32, a = 693.7(2), c = 1627.1(4) pm, wR2 = 0.0762, 525 F² values and 21 variables. The striking structural motifs of the Li₄Pt₃Si structure are silicon atoms with a slightly distorted trigonal prismatic platinum coordination with short Si–Pt distances (238–246 pm). Always two trigonal prisms are condensed via a common Pt₃ triangle, and these double units built up a three-dimensional network by condensation via common corners. The channels left by this prismatic network are filled by two crystallographically independent lithium sites in a 3:1 ratio. The single crystal X-ray data were fully confirmed by neutron powder diffraction and ⁷Li magic-angle spinning (MAS)–nuclear magnetic resonance (NMR) results. The two distinct lithium sites are well differentiated by their ⁷Li isotropic chemical shift and nuclear electric quadrupolar interaction parameters. MAS-NMR spectra reveal signal coalescence effects above 300 K, indicating chemical exchange between the lithium sites on the millisecond timescale. The spectra can be simulated with a simple two-site exchange model. From the resulting temperature-dependent correlation times, an activation energy of 50 kJ/mol is extracted.     

Complex amidoboranes M<Superscript>2</Superscript>[M<Superscript>1</Superscript>(NH<Subscript>2</Subscript>BH<Subscript>3</Subscript>)<Subscript>4</Subscript>] (M<Superscript>1</Superscript> = Al,Ga; M<Superscript>2</Superscript> = Li,Na, K,Rb, Cs)

Structural, spectral, and thermodynamic characteristics of complex amidoboranes M²[M¹(NH₂BH₃)₄] (M¹ = Al, Ga; M² = Li, Na, K, Rb, Cs) were calculated by the B3LYP/def2-SVPD quantum-chemical method. The procedure for the synthesis of these compounds by reactions of alkali metal amidoboranes with aluminum and gallium chlorides was suggested and experimentally tested. Reaction products were characterized by the NMR and IR spectroscopy and X-ray phase analysis.     

Cycling Performance at Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript>|Li Interface

Cyclability of the Li|Li₇La₃Zr₂O₁₂ interface was tested by voltammetry under externally applied potential difference. It was found that the solid electrolyte synthesized in the study contains a minor amount of an impurity in the form of lithium carbonate. This impurity forms, when brought in contact with metallic lithium, carbon that pierces the whole volume of the ceramic separator and produces a channel for a flow of electrons through the material, which leads to a poor cyclability of the solid electrolyte. A possible way to solve the given problem is via a purposeful replacement of the carbonate in the intergrain space of Li₇La₃Zr₂O₁₂ with another crystalline or glassy plasticizer that possesses an acceptable unipolar lithium conductivity (no less than 10^–6 S cm^–1) and forms, when brought in contact with metallic lithium, no electrically conducting compound or a compound capable of reversibly intercalating/deintercalating lithium.     

Silica-supported perchloric acid (HClO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>) as efficient catalyst for the synthesis of tetraazamacrocyclic complexes of transition metals

Silica-supported perchloric acid (HClO₄/SiO₂) was used to catalyze the synthesis of tetraazamacrocyclic complexes of Co(II), Ni(II), Cu(II), and Zn(II) from the corresponding metal chlorides, nitrates, or acetates, isatin, and benzene-1,2-diamine in ethanol. The use of HClO₄/SiO₂ as catalyst allowed the reaction to be performed under stirring at room temperature instead of traditional reflux and completed in two hours. The synthesized complexes were characterized by molar conductance and magnetic susceptibility measurements, IR, electronic, ¹H NMR, and mass spectra, and thermogravimetric and X-ray powder analyses. On the basis of these data, six-coordinate octahedral geometry was proposed for all complexes. The synthesized complexes were also tested for antimicrobial activity.     

Effects of Ni-ion doping on electrochemical characteristics of spinel LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> powders prepared by a spray-drying method

Spinel LiMn_2−x Ni _x O₄ compounds doped with a range of Ni (x=0–0.06) were synthesized by a spray-drying method. The structure and morphology characteristics of the powders were studied in detail by means of X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy. The XRD data reveal that all the samples have well-defined spinel structure, but, with the increase in Ni content, the doped lithium manganese spinels have smaller lattice constant. The undoped and doped spinel LiMn₂O₄ particles are fine, narrowly distributed, and well crystallized. The electrochemical characteristics of the samples are measured in the coin-type cells in a potential range of 3.2–4.35 V vs Li/Li⁺. All cyclic voltammogram curves exhibit two pairs of redox reaction peaks, but, among them, there are some differences about the peak split. With the increase in the Ni content, the specific capacities of the samples decrease slightly, but their cyclic ability increases.     

Pivalates with the M<Superscript>II</Superscript><Subscript>4</Subscript>O<Subscript>4</Subscript> cubane core (M = Co,Ni): synthesis,structure, magnetic properties,and solid-state thermolysis

Methods were developed for the controlled thermal synthesis of high-spin cubane-like pivalates {M^II ₄(μ₃−OR)₄} (M = Co or Ni; R = H or Me) starting from mono-and polynuclear complexes. The solid-state thermal decomposition of the known pivalate clusters [M^II ₄(μ₃−OMe)₄−(μ₂−OOCBu^t)₂(η²−OOCBu^t)₂(MeOH)₄] and the new clusters [M₄^II(μ₃)−OH₄(η¹−OOCBu^t)₃−(μ−(NH₂)₂C₆H₂Me₂)₃(η¹−(NH₂)₂C₆H₂Me₂)₃]⁺(OOCBu^t)− (M = Co or Ni) was studied by differential scanning calorimetry and thermogravimetry. The thermolysis of cubane-like CoII and NiII pivalates is a destructive process. The phase composition of the decomposition products is determined by the nature of coordinated ligands and the structural features of the metal core.     

Quantum-chemical modeling of the electronic structure and chemical bond of Sn<Subscript>0.875</Subscript>M<Subscript>0.125</Subscript>O<Subscript>2</Subscript> (M = Cr,Mn, Co)

The electronic structure of the Sn_0.875M_0.125O₂ compounds (M = Cr, Mn, Co) with a rutile structure and magnetic moments of the transition metal atoms in them were calculated by the ab initio spin-polarized linear muffin-tin orbital method. The electron density and electron localization function maps for these compounds were constructed. Based on these data, the effect of the composition of these phases on the electronic spectrum, chemical bond, and magnetic and transport properties were analyzed.     

Supramolecular architecture of the [M(1-MeIm)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>]<Superscript>2+</Superscript> (M = Ni,Co) complexes with the terephthalate anion

The [M(1-MeIm)₂(H₂O)₄](Tpht) · 4H₂O complexes (where M = Ni, Co; 1-MeIm is 1-methylimidazole; H₂Tpht is terephthalic acid) are synthesized and characterized by X-ray diffraction analysis. The ionic structure is built of the [M(1-MeIm)₂(H₂O)₄]²⁺ cations and (Tpht)^2? anions. The metal ions have a distorted octahedral coordination. The cations and anions are united by hydrogen bonding system.     

Intermolecular complexes of nido-C<Subscript>2</Subscript>B<Subscript>3</Subscript>H<Subscript>7</Subscript> with HF and LiH molecules: the theoretical studies,bonding properties and natural bond orbital (NBO) analysis

The changes in stabilization energy upon the formation of intermolecular hydrogen, dihydrogen and lithium bond complexes between C₂B₃H₇, LiH and HF have been investigated using MP2 method with aug-cc-pVDZ basis set. The interaction of HF with nido-C₂B₃H₇ could occur through the formation of B–H^?δ···^+δH–F, C–H^+δ···F^?δ–H and B–C···H–F classical and non-classical hydrogen bonds. The B–C bonds in backbone of the C₂B₃H₇ as electron donor interact with σ* orbital of HF as electron acceptor. Also interaction of LiH with nido-C₂B₃H₇ resulted in B–C···Li–H and B–H···LiH lithium bonds as well as C–H···H–Li dihydrogen bond complexes. In some of these complexes, LiH interacts with B–C bonds. Results are indicating that more stable complexes belong to interaction of HF and LiH with backbone of the nido-C₂B₃H₇. The AIM and NBO methods were used to analyze the intermolecular interactions; also the electron density at the bond critical point and the charge transfer of obtained complexes were studied.     

The Solid-State-Grinding Synthesis of Maganese-Modified Cobalt Oxides and Application in the Low-Temperature CO Preferential Oxidation in H<Subscript>2</Subscript>-Rich Gases

A series of MnOx modified cobalt oxides with different atomic molar ratios of Mn/(Mn?+?Co) were prepared by a soft reactive grinding route and investigated for CO preferential oxidation in H₂. It was found that as-prepared Mn-doped cobalt oxides exhibited superior activity compared to the single constituted oxides, other Mn–Co–O mixed oxides synthesized by solution-based route, and other grinding-derived mixed metal oxides M–Co–O (M?=?Zn, Ni, Cu, Fe). The grinding-derived MnCo10 catalyst with Mn/(Mn?+?Co) molar ration of 10% showed the best CO oxidation activity and higher selectivity at low temperature. The surface richness of Co³⁺ was not found as increasing the Mn molar ratio in the present work. However, the incoporation of MnOx with proper amount into Co₃O₄ could produce high surface area, high structure defects, and rich surface active oxygen species, while the ability to supply the active oxygen species was suggested to play the crucial role in promoting the catalytic performance of Mn–Co–O mixed oxides.