The role of the rotational state in intermolecular interactions of H2O with H2 and CH3Cl

Rotational-state resolved measurements of H₂O−H₂ and H₂O−CH₃Cl intermolecular interactions were performed. Using light-induced drift as a tool, we measured changes in transport collision ratev upon rovibrational (J, r)-excitation of H₂O. We studied P- and R-branch excitation withJ ranging from O through 9 for H₂O excited in the fundamental asymmetric stretch mode. Combination of P and R data yields the dependencies ofv upon rotational (J) and vibrational (r) quantum numbers separately. For H₂O−CH₃Cl it is found thatv decreases by 25% asJ increases from 0 to 9. For H₂O−H₂ the decrease is only 1.0%. These data seem to exemplify a fundamental aspect of dipole-dipole interaction: the familiar 1r ³ interaction term is highlyJ-dependent. This is attributed to the increasing averaging-out of the dipolar potential as the rotational quantum number increases. Paper dedicated to Professor Edward A. Mason.     

Noncovalent Modification of Nanodiamonds with Tritium-Labeled Pantothenic Acid Derivatives

The efficiency of tritium labeling of salts of pantothenic (HO–R–COOH), hopantenic (HO–R–CH₂–COOH), and 4-D-phosphopantothenic [(HO)₂P(=O)–O–R–COOH] acids [R = CH₂C(CH₃)₂CHOH–CONH(CH₂)₂] with thermal activation of tritium at target temperatures of 77 and 295 K was studied. The phosphate group inhibits the isotope exchange. The tritium-labeled compounds were used for studying the adsorption of pantothenic acid derivatives from aqueous solutions and in the presence of 0.9% NaCl at 297 ± 3 K onto nanodiamonds prepared by detonation synthesis (NDs). Preparation of stable ND suspensions in advance enhances the ability of NDs to adsorb the compounds studied. The parameters of the equation describing the sorption isotherms at different ionic strengths of the solution were calculated. The strength of the adsorbate retention in contact with water, 0.9% NaCl solution, 0.01 M HCl solution, and 40 g L^?1 bovine serum albumin (BSA) solution was determined. The data obtained allow two mechanisms of the adsorbate retention on the ND surface to be considered: reversible adsorption due to ionic interactions and irreversible binding due to hydrophobic interactions. The strongly bound molecules undergo slow desorption in the presence of BSA. The revealed trends confirm high potential of NDs as a drug delivery platform.

     

Synthesis and structural studies of a new potassium uranyl selenate K(H5O2)[(UO2)2(SeO4)3(H2O)] with strongly deformed layers

Single crystals of a new uranyl selenate, K(H₅O₂)[(UO₂)₂(SeO₄)₃(H₂O)] (I), were prepared by isothermal evaporation at room temperature. The crystal structure of I was solved by the direct method (space group P2₁/c; a = 11.456(2), b = 10.231(1), c = 14.809(2) ?; β = 101.901(4)°, V = 1698.4(4) ?³; Z = 4) and refined to R ₁ = 0.0547 (wR ₂ = 0.0825) for 3375 reflections with |F _o| ≥ 4σ _F . The structure of I is based on layers of the composition [(UO₂)₂(SeO₄)₃(H₂O)]²⁻. The charge of the inorganic layer is compensated by potassium and oxonium ions located in the interlayer space. Each potassium ion is coordinated by seven oxygen atoms belonging to uranyl selenate layers, including uranyl oxygen atoms, which leads to bending of uranyl selenate structural elements.     

Role of Al additions in wear control of nanocrystalline Mo(Si1−xAlx)2 coatings prepared by double cathode glow discharge technique

Abstract

Four kinds of nanocrystalline Mo(Si_1?xAl_x)₂ coatings with differing Al contents are prepared onto a Ti–6Al–4V substrates by a double cathode glow discharge apparatus. The microstructural features of the deposited coatings were characterised by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. These coatings are composed of the equiaxed C40–MoSi₂ grains with the average grain size of ～5 nm. Nano-indentation measurements indicated that the hardness H, elastic modulus E and the H/E or H³/E² ratio of the nanocrystalline Mo(Si_1?xAl_x)₂ coatings slightly increase with the increase in Al content. The tribological behaviour of the nanocrystalline Mo(Si_1?xAl_x)₂ coating sliding against a ZrO₂ ceramic ball at room temperature has been compared using a ball-on-disc type tribometer under unlubricated conditions. Experimental results showed that the specific wear rates of the nanocrystalline Mo(Si_1?xAl_x)₂ coatings decrease with increasing Al content and are dramatically reduced by more than 1–2 orders of magnitude over the uncoated Ti–6A1–4V. The enhancement of wear resistance of the nanocrystalline Mo(Si_1?xAl_x)₂ coatings by Al additions is correlated with the increased mechanical properties and the forming oxide layer by tribochemical reactions.     

Hydrothermal syntheses, structures and magnetic properties of coordination frameworks of divalent transition metals

The hydrothermal syntheses, single-crystal X-ray structures and magnetic properties of [Co(C₄O₄)(H₂O)₂] (1), [Co₃(OH)₂(C₄O₄)₂] · 3H₂O (2) and [Fe(OH)₂(C₄O₄)] (3) are described. Pale yellow cubes of 1 and brown red crystals of 2 were obtained from the reaction of Co(OH)₂ and squaric acid at 200 °C. Brown needle of 3 were obtained similarly from Fe(SO₄) · 7H₂O, squaric acid and NaOH. 1 consists of a cubic sodalite arrangement with empty cavities where the Co atoms are connected by μ₄-squarate and two trans-water molecules each, while 2 and 3 contain metal-hydroxide double-chains of edge-sharing octahedral, brucite-type for 2 and goethite for 3, connected by μ₆-squarate. 2 contains water molecules in the channels which can be removed and re-inserted repeatedly without loss of crystallinity. All three compounds possess 3D frameworks made up of coordination and hydrogen bonds. 1 behaves as a paramagnet while 2 and 3 are antiferromagnets and 2 transforms to a ferromagnet reversibly upon dehydration and rehydration. The structures of two one-dimensional polymers employing 2,5-pyridinedicarboxylate, [Co₂(H₂O)₆(2,5-pydc)₂] · 2H₂O (4) and Cu(2,5-pydc)₂ (5), are also reported.     

Study on structural phase transitions and relaxation processes of Cs2Co(SO4)2·6H2O and Cs2Zn(SO4)2·6H2O crystals

The structural phase transitions and relaxation processes of Cs₂Co(SO₄)₂·6H₂O and Cs₂Zn(SO₄)₂·6H₂O single crystals were investigated, with the phase transitions of both crystals being determined from NMR data. The spin–lattice relaxation time, T₁, of the ¹³³Cs nucleus in two crystals undergoes a significant change near the phase transition temperature, T_C, and these changes coincide with the changes in the splitting of the ¹³³Cs resonance lines. The variations in the temperature dependence for the splitting of the ¹³³Cs resonance lines and T₁ near T_C are related to changes in the symmetry of surrounding Cs⁺. In addition, the ¹³³Cs T₁ of Cs₂Co(SO₄)₂·6H₂O, which contains paramagnetic ions, was found to be shorter than that of Cs₂Zn(SO₄)₂·6H₂O. This relaxation time is inversely proportional to the square of the magnetic moment of the paramagnetic ions. The differences between the ¹³³Cs T₁ of these compounds are probably due to the differences between the electronic structures of their metal ions.     

Efficient and green oxidative degradation of methylene blue using Mn-doped ZnO nanoparticles (Zn1−xMnxO)

Mn-doped ZnO nanoparticles, Zn_1?xMn_xO, were synthesised by a polyethylene glycol (PEG) sol–gel method and the physicochemical properties of compounds were characterised by atomic absorption spectroscopy (AAS), energy-dispersive X-ray analysis, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The catalytic degradation of an organic dye, methylene blue (MB), in the presence of Zn_1?xMn_xO as the catalyst and hydrogen peroxide (H₂O₂) as the oxidant at room temperature in water has been studied. Effects of oxidant, catalyst amount, catalyst composition, pH value of the solution and an OH-radical scavenging agent on the degree of the decomposition of MB dye were also studied.     

Synthesis and Properties of Neptunium(V) Propionates

From propionate-containing solutions of Np(V), the crystalline compounds NpO₂OOCC₂H₅·nH₂O with n = 1 or 2 and M(NpO₂)₂(OOCC₂H₅)₃·H₂O with M = NH₄ or Cs were separated. Their X-ray powder patterns were recorded and behavior at heating was studied. The IR and electronic absorption spectra suggest that, in these compounds, the NpO₂ ⁺ ions are coordinated with each other to form cation-cation bonds involving all yl oxygen atoms.     

Chemical Thermodynamics of the Compounds AIIUO2(SO4)2·nH2O (AII = Mn, Fe, Co, Ni, Cu, Zn)

The standard enthalpies of formation of anhydrous 3d transition metal uranyl sulfates and their pentahydrates at 298.15 K were determined by reaction calorimetry. The heat capacities of the compounds A^IIUO₂(SO⁴)₂·5H₂O (A^II = Mn, Fe, Co, Ni, Cu, Zn) and CuUO₂(SO₄)₂ at 7– 300 K were determined by adiabatic vacuum calorimetry, and the thermodynamic functions of these compounds were calculated. The standard entropies and Gibbs energies of formation of these compounds at 298.15 K were determined. The thermodynamics of dehydration of A^IIUO₂(SO₄)₂·5H₂O and of the precipitate-solution equilibria involving these compounds were studied. __________ Translated from Radiokhimiya, Vol. 47, No. 2, 2005, pp. 110–122. Original Russian Text Copyright ? 2005 by Karyakin, Knyazev, Gavrilova.     

Hydrothermal synthesis of LiFePO<Subscript>4</Subscript> as a cathode material for lithium batteries

LiFePO₄ (space group: Pnma) was prepared by hydrothermal method at 170 °C. LiFePO₄ was prepared from precursor solutions consisting of FeSO₄ · 7H₂O, (NH₄)₂HPO₄, and three kinds of Li sources. LiCl, Li(CH₃COO), and LiOH · H₂O were used as Li sources. The pH of the precursor solution varied depending on Li source. The particle size, particle shape, and crystal texture of the obtained LiFePO₄ changed depending on pH. The electrochemical properties of the prepared LiFePO₄ were characterized as a cathode material for lithium batteries in an organic electrolyte at room temperature. The LiFePO₄ particle prepared from the precursor solution with Li(CH₃COO) was flake-like crystal (particle size: 1–2 μm) and had a preferred crystal orientation with a (020) texture. This LiFePO₄ exhibited a discharge capacity of 147 mA h g⁻¹, which was 85% of the theoretical capacity 170 mA h g⁻¹.     

Synthesis and Structure of U(VI), Np(VI), and Pu(VI) 2-Fluorobenzoates

The compounds NH₄[AnO₂(C₆H₄FCOO₃], where An = U (I), Np (II), or Pu (III), CgH₄COO^? is the 2-fluorobenzoate anion, were synthesized and studied by single crystal X-ray diffraction. Compounds I–III are isostructural and crystallize in the cubic system, space group P2₁3, Z = 4. The main structural units of I–III are mononuclear complexes [AnO₂(C₆H₄COO)₃]^? belonging to crystal-chemical group AB₃¹ (A = AnO₂²⁺, B⁰¹ = C₆H₄FCOO^?). The actinide contraction in the structures of I–III is manifested in a regular decrease in the lengths of the An=0 bonds in the AnO₂²⁺ cations and in the volumes of the Voronoi-Dirichlet polyhedra (VDPs) of the An atoms in the series U-Np-Pu. The intermolecular interactions in crystal structures of I–III were analyzed by the method of molecular VDPs.

     

X-ray powder diffraction and IR study of NaMg(H2O)2[BP2O8]·H2O and NH4Mg(H2O)2[BP2O8]·H2O

NaMg(H₂O)₂[BP₂O₈]·H₂O was prepared by hydrothermal synthesis and was characterized by X-ray powder difraction and IR method. The title compound was synthesized from MgCl₂·6H₂O, NaBO₃·4H₂O, and (NH₄)₂HPO₄ with variable molar ratios using hydrothermal method by heating at 165 °C for 3 days. The X-ray powder diffraction data was indexed in hexagonal system, the unit cell parameters were found to be as a = 9.428, c = 15.82 Å, Z = 4 and the space group is P6₁22. It is isostructural with M^lM^ll(H₂O)[BP₂O₈] type compounds where M^l = Na, K; M^ll = Mg, Mn, Fe, Co, Ni and Zn. In addition NH₄Mg(H₂O)₂[BP₂O₈]·H₂O was also synthesized the first time in this research. Its unit cell parameters and hkl values were in good agreement with the sodium magnesium compound. The unit cell parameters are a = 9.529, c = 15.736 Å. The indexed X-ray powder diffraction data of both compounds which were not reported in the literature is presented in this work. The IR data of NaMg(H₂O)₂[BP₂O₈]·H₂O is also reported.     

Preparation and sintering behaviour of a fine grain BaTiO<Subscript>3</Subscript> powder containing 10 mol% BaGeO<Subscript>3</Subscript>

The formation of solid solutions of the type [Ba(HOC₂H₄OH)₄][Ti_1−x Ge _x (OC₂H₄O)₃] as Ba(Ti_1−x /Ge _x )O₃ precursors and the phase evolution during thermal decomposition of [Ba(HOC₂H₄OH)₄][Ti_0.9Ge_0.1(OC₂H₄O)₃] (1) are described herein. The 1,2-ethanediolato complex 1 decomposes above 589 °C to a mixture of BaTiO₃ and BaGeO₃. A heating rate controlled calcination procedure, up to 730 °C, leads to a nm-sized Ba(Ti_0.9/Ge_0.1)O₃ powder (1a) with a specific surface area of S = 16.9 m²/g, whereas a constant heating rate calcination at 1,000 °C for 2 h yields a powder (1b) of S = 3.0 m²/g. The shrinkage and sintering behaviour of the resulting Ba(Ti_0.9/Ge_0.1)O₃ powder compacts in comparison with nm-sized BaTiO₃ powder compacts (2a) has been investigated. A two-step sintering procedure of nm-sized Ba(Ti_0.9/Ge_0.1)O₃ compacts (1a) leads, below 900 °C, to ceramic bodies with a relative density of ≥90%. Furthermore, the cubic ⇆ tetragonal phase transition temperature has been detected by dilatometry, and the temperature dependence of the dielectric constant (relative permittivity) has also been measured.     

Heterogeneous equilibria in aqueous solutions of uranophosphates MII(PUO6)2·nH2O (MII = Mg2+, Ca2+, Sr2+, Ba2+)

The stability of uranophosphates M^II(PUO₆)₂·nH₂O (M^II = Mg, Ca, Sr, Ba) in aqueous solutions at pH from 0 to 14 was studied. These compounds preserve their composition and structure in the interval of pH 1–11 and congruently pass into the solution within the limits of their solubility. In strongly acidic media (pH < 1), alkaline-earth metal uranophosphates transform into uranophosphoric acid HPUO₆·4H₂O. In alkaline solutions at pH > 11, the uranophosphates MII(PUO₆)₂·nH₂O irreversibly transform into diuranates. Using the methods of equilibrium thermodynamics, the solubility products and Gibbs functions of formation of alkalineearth metal uranophosphates were calculated, the solubility curves were calculated and experimentally confirmed, and the speciation diagrams of U(VI) and P(V) in solutions and in equilibrium solid phases were constructed.     

Photoluminescent lead(II) coordination polymers stabilised by bifunctional organoarsonate ligands

Abstract

Four lead(II) coordination polymers were isolated under hydro(solvo)thermal conditions. The applied synthetic methodology takes advantage of the coordination behaviour of a new bifunctional organoarsonate ligand, 4-(1, 2, 4-triazol-4-yl)phenylarsonic acid (H₂TPAA) and involves the variation of lead(II) reactants, metal/ligand mole ratios, and solvents. The constitutional composition of the four lead(II) coordination polymers can be formulated as [Pb₂(TPAA)(HTPAA)(NO₃)]·6H₂O (1), [Pb₂(TPAA)(HTPAA)₂]·DMF·0.5H₂O (DMF = N, N-Dimethylformamide) (2), [Pb₂Cl₂(TPAA)H₂O] (3), and [Pb₃Cl(TPAA)(HTPAA)₂H₂O]Cl (4). The compounds were characterized by single-crystal and powder x-ray diffraction techniques, thermogravimetric analyses, infra-red spectroscopy, and elemental analyses. Single-crystal x-ray diffraction reveals that 1 and 2 represent two-dimensional (2D) layered structures whilst 3 and 4 form three-dimensional (3D) frameworks. The structures of 1, 2, and 4 contain one-dimensional (1D) {Pb^II/AsO₃} substructures, while 3 is composed of 2D {Pb^II/AsO₃} arrays. Besides their interesting topologies, 1–4 all exhibit photoluminescence properties in the solid state at room temperature.     

Crystal Structure of (H3O)6[(UO2)5(SeO4)8(H2O)5](H2O)5

Crystals of (H₃O)₆[(UO₂)₅(SeO₄)₈(H₂O)₅](H₂O)₅ were prepared from aqueous solutions by evaporation. The crystal structure [monoclinic system, space group P2₁/m, a = 13.835(2), b = 13.4374(16), c = 14.310(3) Å, β = 108.004(14)°, V = 2530.1(7) Å ³] was solved by the direct method and refined to R ₁ = 0.090 for 4409 reflections with |F _hkl ≥ 4σ|F _hkl |. The structure is based on [(UO₂)₅(SeO₄)₈(H₂O)₅]⁶⁻ layers arranged parallel to the (101) plane; these layers have a unique topological structure. The U(1)O₆(H₂O) and U(3)O₆(H₂O) linked through selenate groups form chains running along [ [`1]\bar 1 01] direction. The chains are combined in layers by U(2)O₆(H₂O) bipyramids. The layers are linked with each other by hydrogen bonds through the H₂O and H₃O⁺ groups located between the layers.     

Strongly Coupled Pyridine‐V2O5·nH2O Nanowires with Intercalation Pseudocapacitance and Stabilized Layer for High Energy Sodium Ion Capacitors

Developing pseudocapacitive cathodes for sodium ion capacitors (SICs) is very significant for enhancing energy density of SICs. Vanadium oxides cathodes with pseudocapacitive behavior are able to offer high capacity. However, the capacity fading caused by the irreversible collapse of layer structure remains a major issue. Herein, based on the Acid–Base Proton theory, a strongly coupled layered pyridine‐V₂O₅·nH₂O nanowires cathode is reported for highly efficient sodium ion storage. By density functional theory calculations, in situ X‐ray diffraction, and ex situ Fourier‐transform infrared spectroscopy, a strong interaction between protonated pyridine and V?O group is confirmed and stable during cycling. The pyridine‐V₂O₅·nH₂O nanowires deliver long‐term cyclability (over 3000 cycles), large pseudocapacitive behavior (78% capacitive contribution at 1 mV s^?1) and outstanding rate capability. The assembled pyridine‐V₂O₅·nH₂O//graphitic mesocarbon microbead SIC delivers high energy density of ≈96 Wh kg^?1 (at 59 W kg^?1) and power density of 14 kW kg^?1 (at 37.5 Wh kg^?1). The present work highlights the strategy of realizing strong interaction in the interlayer of V₂O₅·nH₂O to enhance the electrochemical performance of vanadium oxides cathodes. The strategy could be extended for improving the electrochemical performance of other layered materials.     

State of uranyl phosphates and arsenates in aqueous solutions

The state of uranyl phosphates and arsenates (UO₂)₃(PO₄)₂·nH₂O and (UO₂)₃(AsO₄)₂·nH₂O in aqueous solutions in the interval of pH 1–14 was studied by X-ray diffraction, IR spectroscopy, thermography, and chemical analysis. The composition and structure of the initial solid phases vary depending on the solution acidity. The equilibrium constants of the reactions occurring in the heterogeneous systems (UO₂)₃(B^VO₄)₂·nH₂O (B^V = P, As)-aqueous solution were calculated. The speciation diagrams of the solid phases and equilibrium solutions were plotted.     

Physical Chemistry of the Compounds AI I(BVUO6)2·nH2O (AI I = Mn, Ni, Co, Zn, Cd; BV = P, As)

The ion exchange between an aqueous solution of a bivalent metal chloride (A^{I I} = Mn, Ni, Co, Zn, Cd) and crystalline phases HB^VUO₆·4H₂O (B^V = P, As) was studied. The exchange constants and standard Gibbs energies of formation of the crystalline compounds A^{I I}(B^VUO₆)₂·nH₂O were calculated.