Filling up another Gap: Synthesis and Crystal Structure of Ba2H3I

Colorless and transparent single crystals of Ba2H3I were obtained by reacting Ba with dried and sublimed NH4I in a 4 : 1 molar ratio in silica-jacketed Nb ampoules at 1100 K for 13 h. The crystal structure of the title compound was determined and refined by means of single-crystal X-ray diffraction. Ba2H3I crystallizes in a stuffed anti-CdI2 structure isotypic to Sr2H3I in the space group P3̄m1 (no. 164) with the lattice parameters a = 451.86(12) and c = 811.84(23) pm. The structural results for Ba2H3I are consistent with bond lengths and coordination geometries of related binary and ternary hydrides

Ba9[NbN4]2O[Cn2] – Synthesis, Crystal Structure and Raman Spectrum

Red transparent single crystals of Ba9[NbN4]2O[CN2] were synthesised by the reaction of BaO coated Ba metal, C and Nb powder in arc-welded Nb ampoules at 1300 K. The title compound was characterised by X-ray single crystal diffraction (P1̅ , a = 799.05(2), b = 962.61(2) and c = 1264.38(4) pm; α = 75.859(1), β = 85.745(1) and γ = 87.8621(8)°; Z = 2) and Raman spectroscopy (νsym = 1234 and δ = 632/658/668 cm−1). It now seems likely that a nitride-azide compound we previously reported, Ba9[NbN4]2N[N3], does not exist, but is in fact the title compound.

Single-Crystal Structures and Vibrational Spectra of Li[SCN] and Li[SCN] · 2H2O

The crystal structure of Li[SCN] · 2 H2O has been determined by single-crystal X-ray diffraction on commercially available material. Crystals of this compound are colorless, transparent and hygroscopic. Li[SCN] · 2H2O adopts the orthorhombic space group Pnma with the cell parameters a = 572.1(3), b = 809.3(4) and c = 966.9(4) pm and Z = 4. Li[SCN] was obtained by dehydration of the afore-mentioned dihydrate and also crystallizes orthorhombically in Pnma with the lattice parameters a = 1215.1(3), b = 373.6(1) and c = 529:9(2) pm (Z = 4). Both compounds contain Li+ cations in sixfold coordination. Four water molecules and two nitrogen-attached thiocyanate anions [SCN]- arrange as trans-octahedra [Li(OH2)4(NCS)2]- in the case of Li[SCN] · 2 H2O. Anhydrous Li[SCN] displays fac-octahedra [Li(NCS)3(SCN)3]5- with six thiocyanate anions grafting via both nitrogen and sulfur atoms, three each. Infrared and Raman spectra of both compounds were recorded and a DSC=TG measurement was performed on Li[SCN] · 2 H2O.

Different Structural Models of YB2C2 and GdB2C2 on the Basis of Single-Crystal X-Ray Data

Samples of YB2C2 and GdB2C2 were synthesized by arc-melting and subsequent annealing of the products. Single crystals of the title compounds were examined with single-crystal X-ray methods. Five different tetragonal unit cell settings from the literature (obtained on the basis of symmetry considerations) were used for the refinement of the crystal structure of YB2C2, but a converging refinement was only achieved for the structural model in the space group P4=mbm (no. 127, Z = 2) with a = 533:27(3) and c = 354:58(3) pm, without obvious inconsistencies. Nevertheless, the results for the five different unit cell settings are compared and discussed. A refinement of the crystal structure of the isotypic compound GdB2C2 was also performed with the lattice parameters a = 537:46(6) and c = 364:98(11) pm. Neither EuB2C2 nor YbB2C2 were obtained by melting coldpressed pellets with the nominal composition RE1.5B2C2 in an arc-furnace or an induction furnace, or by just heating the pellets in sealed Ta ampoules

Crystal Structure and Magnetic Susceptibility of Ce8Pd24Sb

The ternary compound Ce8Pd24Sb is very close in composition to the intermediate valent binary CePd3. A single crystal study yielded a cubic cell with a = 8.461 (1)Å, Pm3̄m symmetry with wR2 = 0.0412 based on 1453 reflections (222 unique) and 16 parameters. This new structure type is composed of distorted perovskite and Cu3Au subcells arranged with the perovskite-like units centred on the corners of the cube. Fitting the magnetic susceptibility data above 100K to a Curie-Weiss expression yielded a Weiss constant of -15(3)K (antiferromagnetic) and an effective high temperature moment per cerium of 2.45(4)/μв indicating trivalent cerium. No ordering was observerd above 3K.

A Metal Nitride Carbodiimide with a Stuffed Skutterudite-type Structure: Synthesis, Crystal Structure and IR Spectra of (Ba6N5/6)2[NbN4][CN2]6

Coppery-red, transparent single crystals of (Ba6N5/6)2[NbN4][CN2]6 (Im¯3, no. 204, a =1125.83(3) pm, Z = 2) are obtained by the reaction of Ba2N and ZnCN2 with the container walls of the arc-welded Nb ampoules at 1100 K. The title compound assumes a stuffed skutterudite-type structure in which edge-sharing (Ba6N5/6) octahedra form large voids which are occupied by either [NbN4] tetrahedra or by [N=C=N]2− units with symmetric C=N bond lengths of d = 121.8(6) pm but a bond angle deviating significantly from linearity (∡ (N-C-N) = 175.3(9)°). The IR spectra corroborate this crystallographic result by the fact that all fundamental vibrations are visible in the IR spectrum [ν1 = 1262 (symmetric stretching mode); ν2 = 1957/2009 (antisymmetric stretching mode); ν3 = 611/633/653 cm−1 (bending modes)], which is symmetry forbidden for [N=C=N]2− units having D∞h symmetry but expected for the C2v symmetry found in the title compound.

Unusual Bonding in Ternary Nitrides: Preparation, Structure and Properties of Ce2MnN3

Ce2MnN3 was prepared by reaction of cerium nitride and manganese with nitrogen gas at 900 °C. It crystallizes isotypic to AC2MN3 (Ac = U, Th; M = Cr, Mn) and Ce2CrN3, space group Immm (No. 71), a = 3.74994(6) Å, b = 3.44450(6) Å and c = 12.4601(2) Å. The manganese atoms are coordinated in a nearly square planar fashion by four nitrogen atoms. These corner-connected MnN4 units form infinite 1 ∞[MnN2N2/2] chains, which run parallel to each other along the crystallographic a-axis, forming the motif of hexagonal rod packing. Cerium atoms connect the chains into a three-dimensional network. The results of measurements of the magnetic susceptibility, as well as of the electrical resistivity suggest metallic behavior. Electronic effects leading to shorter bonds between manganese and bridging nitrogen atoms than between manganese and terminal nitrogen atoms in the 1 ∞[MnN2N2/2] chains were investigated through extended Hückel and LMTO band structure calculations. Issues pertaining to stability of this and some other nitridometallate structures are discussed.

Rietveld Refinement of the Crystal Structure of α-Be3N2 and the Experimental Determination of Optical Band Gaps for Mg3N2, Ca3N2 and CaMg2N2

α-Be3N2 powder was obtained by reacting Be metal with dry, flowing N2 at 1600 K. The product contained 5.9(7) wt.% of BeO. The anti-bixbyite structure suggested earlier was verified through Rietveld refinement on the basis of X-ray powder data (Ia3 (#206); a = 814.518(6) pm). The optical band gaps of α-Be3N2, Mg3N2 and Ca3N2 are compared with newly measured values for Mg3N2, Ca3N2 and CaMg2N2.

New Calcium Hydride Halides with Familiar Structures. Syntheses and Crystal Structures of Ca7H12Cl2 and Ca2H3Br

Single crystals of Ca7H12Cl2 and Ca2H3Br were obtained by reacting stoichiometric amounts of CaH2 and CaX2 (X = Cl, Br) at 1300 K in the presence of surplus Ca metal for 13 h in silicajacketed Nb ampoules. The crystal structures of the new compounds were determined by means of single-crystal X-ray diffraction. Ca7H12Cl2 crystallizes isotypical to Ba7Cl2F12 and Sr7H12Cl2 in the hexagonal space group P¯6 (no. 174) with the lattice parameters a = 936.51(8), c = 368.65(2) pm, while Ca2H3Br crystallizes in a stuffed anti-CdI2 structure isotypical to Ba2H3Cl and therefore adopts the space group P¯3m1 (no. 164) with the lattice parameters a = 391.37(6) and c = 697.04(13) pm. The structural results are corroborated by EUTAX calculations on the title compounds and the comparison of these results to those for CaH2, CaX2 and CaHX (X = Cl, Br). Similar calculations on the hypothetical compound “Ca7H12Br2” give a possible explanation for the preferred formation of the compound Ca2H3Br.

Calcium Carbodiimide Compounds Revisited – Syntheses, Single Crystal Structure Determination and Vibrational Spectra of Ca11N6[CN2]2, Ca4N2[CN2] and Ca[CN2]

Single crystals of Ca11N6[CN2]2 (dark red needles, tetragonal, P42/mnm (no. 136), a = 1456.22(5), and c = 361.86(2) pm, Z = 2), Ca4N2[CN2] (transparent yellow needles, orthorhombic, Pnma (no. 62), a = 1146.51(11), b = 358.33(4), and c = 1385.77(13) pm, Z = 4) and Ca[CN2] (transparent, colorless, triangular plates, rhombohedral, R3̅m (no. 166), a = 369.00(3), and c = 1477.5(3) pm, Z = 3) were obtained by the reaction of Na2[CN2], CaCl2 and Ca3N2 (if demanded by stoichiometry) in arc-welded Ta ampoules at temperatures between 1200 - 1400 K. Their crystal structures were re-determined by means of single crystal X-ray structure analyses. Additionally, the Raman spectra were recorded on these same single crystals, whereas the IR spectra were obtained with the KBr pellet technique. The title compounds exhibit characteristic features for carbodiimide units with D∞h symmetry (d(C-N) = 121.7 - 123.8 pm and ∡ (N-C-N) = 180°). The vibrational frequencies of these units are in the expected range (Ca11N6[CN2]2: νs = 1230, νs = 2008; δ = 673/645/624 cm−1; Ca4N2[CN2]: νs = 1230, νs = 1986; δ = 672/647 cm−1; Ca[CN2]: νs = 1274, νs = 2031, δ = 668 cm−1). The structural results are more precise than the previously reported data, and with the newly attained Raman spectrum of Ca11N6[CN2]2 we correct data reported earlier.

An Alternative Crystal Structure of Yb26B12O57 – X-Ray Structure Determination on Flux-synthesized Single Crystals

Transparent and colorless single crystals of Yb26B12O57 were obtained by reacting Yb2O3 and B powder at 1000 °C in the presence of a KCl flux for 24 h in silica-jacketed Nb ampoules and subsequent removal of the flux by washing with water. Yb26B12O57 crystallizes in the monoclinic space group C2/m (no. 12, Z = 1) with the lattice parameters a = 2454:1(3), b = 357:78(4), c = 1426:7(2) pm and β = 115:111(6)°, and its structure differs slightly from that of a known compound with the same stoichiometry. Raman spectra of single crystals of the title compound were recorded and compared to those of known borate compounds

Synthesis, Raman Spectrum and Single-Crystal Structure of CaBa8[CN2]6O2(N0.5H0.5)

Colorless, transparent single crystals of CaBa8[CN2]6O2(N0.5H0.5) (R3̄ (no. 148), a = 996.94(4) and c = 1803.18(8) pm, Z = 3) were obtained by the reaction of Ca3N2, Ba2N and NaHCN2 (of which one of the latter two most likely was contaminated with some oxygen impurity) in arcwelded Nb ampoules at 1200 K. The title compound consists of distorted (H/N)Ba6 octahedra which share two of their opposite faces with OBa4 tetrahedra interconnected by [N=C=N]2- units of Ca(N=C=N)6 octahedra with C=N bond lengths of 121.9(6) and 124.3(6) pm and with a bond angle deviating from linearity with (N-C-N) = 175:9(5)°. A Raman spectrum obtained from the crystal used for the structure determination indicates the presence of the [N=C=N]2- unit.

Structurally ordered intermetallic platinum-cobalt core-shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts

To enhance and optimize nanocatalyst performance and durability for the oxygen reduction reaction in fuel-cell applications, we look beyond Pt-metal disordered alloys and describe a new class of Pt-Co nanocatalysts composed of ordered Pt(3)Co intermetallic cores with a 2-3 atomic-layer-thick platinum shell. These nanocatalysts exhibited over 200% increase in mass activity and over 300% increase in specific activity when compared with the disordered Pt(3)Co alloy nanoparticles as well as Pt/C. So far, this mass activity for the oxygen reduction reaction is the highest among the Pt-Co systems reported in the literature under similar testing conditions. Stability tests showed a minimal loss of activity after 5,000 potential cycles and the ordered core-shell structure was maintained virtually intact, as established by atomic-scale elemental mapping. The high activity and stability are attributed to the Pt-rich shell and the stable intermetallic Pt(3)Co core arrangement. These ordered nanoparticles provide a new direction for catalyst performance optimization for next-generation fuel cells.

Tuning oxygen reduction reaction activity via controllable dealloying: a model study of ordered Cu3Pt/C intermetallic nanocatalysts

A promising electrocatalyst prototype of low Pt mole fraction, intermetallic nanoparticles of Cu(3)Pt, has been prepared using a simple impregnation-reduction method, followed by a post heat-treatment. Two dealloying methods (electrochemical and chemical) were implemented to control the atomic-level morphology and improve performance for the oxygen reduction reaction (ORR). The morphology and elemental composition of the dealloyed nanoparticles were characterized at angstrom resolution using an aberration-corrected scanning transmission electron microscope equipped with an electron energy loss spectrometer. We found that the electrochemical dealloying method led to the formation of a thin Pt skin of ca. 1 nm in thickness with an ordered Cu(3)Pt core structure, while chemical leaching gave rise to a "spongy" structure with no ordered structure being preserved. A three-dimensional tomographic reconstruction indicated that numerous voids were formed in the chemically dealloyed nanoparticles. Both dealloying methods yielded enhanced specific and mass activities toward the ORR and higher stability relative to Pt/C. The spongy nanoparticles exhibited better mass activity with a slightly lower specific activity than the electrochemically dealloyed nanoparticles after 50 potential cycles. In both cases, the mass activity was still enhanced after 5000 potential cycles.

A silica sol-gel design strategy for nanostructured metallic materials

Batteries, fuel cells and solar cells, among many other high-current-density devices, could benefit from the precise meso- to macroscopic structure control afforded by the silica sol-gel process. The porous materials made by silica sol-gel chemistry are typically insulators, however, which has restricted their application. Here we present a simple, yet highly versatile silica sol-gel process built around a multifunctional sol-gel precursor that is derived from the following: amino acids, hydroxy acids or peptides; a silicon alkoxide; and a metal acetate. This approach allows a wide range of biological functionalities and metals--including noble metals--to be combined into a library of sol-gel materials with a high degree of control over composition and structure. We demonstrate that the sol-gel process based on these precursors is compatible with block-copolymer self-assembly, colloidal crystal templating and the Stöber process. As a result of the exceptionally high metal content, these materials can be thermally processed to make porous nanocomposites with metallic percolation networks that have an electrical conductivity of over 1,000 S cm(-1). This improves the electrical conductivity of porous silica sol-gel nanocomposites by three orders of magnitude over existing approaches, opening applications to high-current-density devices.

AlkalineEarthMetal-Hydride-Iodide Compounds: Syntheses andCrystal Structures of Sr2H3I and Ba5H2I3.9(2)O2

Single crystals of Sr2H3I andBa5H2I3.9(2)O2 were obtained by reacting Sr or Ba, respectively, with dried and sublimed NH4I in a 4 : 1 molar ratio in silica-jacketed Nb ampoules for 13 h at 1200 K. The crystal structures of the new compounds have been determined by means of single-crystal X-ray diffraction. Sr2H3I crystallizes in a stuffed anti-CdI2 structure isotypic to Ba2H3Cl in the space group P3m1 (no. 164) with the lattice parameters a = 426.0(1) and c = 774.9(2) pm, while Ba5H2I3.9(2)O2 crystallizes in a new structure type in the space group Cmcm (no. 63) with the lattice parameters a = 1721.0(2), b = 1452.5(2) and c = 639.03(9) pm. The structural results for Sr2H3I are corroborated by EUTAX calculations. For the disordered compound Ba5H2I3.9(2)O2, EUTAX calculations on an approximated, ordered structural model were used to find possible insights into the disorder

Cosputtered composition-spread reproducibility established by high-throughput x-ray fluorescence

We describe the characterization of sputtered yttria-zirconia composition spread thin films by x-ray fluorescence (XRF). We also discuss our automated analysis of the XRF data, which was collected in a high throughput experiment at the Cornell High Energy Synchrotron Source. The results indicate that both the composition reproducibility of the library deposition and the composition measurements have a precision of better than 1 atomic percent.

High energy x-ray diffraction/x-ray fluorescence spectroscopy for high-throughput analysis of composition spread thin films

High-throughput crystallography is an important tool in materials research, particularly for the rapid assessment of structure-property relationships. We present a technique for simultaneous acquisition of diffraction images and fluorescence spectra on a continuous composition spread thin film using a 60 keV x-ray source. Subsequent noninteractive data processing provides maps of the diffraction profiles, thin film fiber texture, and composition. Even for highly textured films, our diffraction technique provides detection of diffraction from each family of Bragg reflections, which affords direct comparison of the measured profiles with powder patterns of known phases. These techniques are important for high throughput combinatorial studies as they provide structure and composition maps which may be correlated with performance trends within an inorganic library.

Ordered three- and five-ply nanocomposites from ABC block terpolymer microphase separation with niobia and aluminosilicate sols

We report the first use of a non-frustrated block terpolymer for the synthesis of highly ordered oxide nanocomposites containing multiple plies. The morphological behavior of 15 ISO-oxide nanocomposites was investigated spanning a large range of compositions along the ƒ(I)=ƒ(S) isopleth using aluminosilicate and niobia sols. Morphologies were determined by TEM and SAXS measurements. Four morphologies were identified, including core-shell hexagonal, core-shell double gyroid, three-domain lamellae, and core-shell inverse-hexagonal, in order of increasing O+oxide vol fraction. All of the resulting nanocomposites had three- or five-ply morphologies containing domains that were continuous in one, two, or three dimensions. The five-ply core-shell double gyroid phase was only found to be stable when the O+oxide domain was a minority. Removal of the polymer enabled simple and direct synthesis of mesoporous oxide materials while retaining the ordered network structure. We believe that advances in the synthesis of multi-ply nanocomposites will lead to advanced materials and devices containing multiple plies of functional materials.

Methanol electrooxidation on PtRu bulk alloys and carbon-supported PtRu nanoparticle catalysts: a quantitative DEMS study

Methanol electrooxidation on smooth Pt and PtRu bulk alloys and carbon-supported Pt and PtRu nanoparticle catalysts has been studied using cyclic voltammetry and potential step chronoamperometry combined with differential electrochemical mass spectrometry (DEMS). The current efficiencies for generated CO2 and methyl formate were calculated from Faradaic current (coulometric charge) and mass spectrometric currents (charges) at m/z=44 and m/z=60. The effects of Ru content in PtRu catalysts, catalyst loading/roughness, and the concentration of sulfuric acid as supporting electrolyte on the reaction kinetics and product distribution during methanol electrooxidation have been investigated. The results indicate that Pt-rich PtRu alloys and carbon-supported PtRu catalysts with ca. 20 atom % Ru content exhibit the highest catalytic activity for methanol electrooxidation, that is, the highest Faradaic current and the highest current efficiency for CO2 generation at low applied potentials. As the catalyst loading/roughness increases, the current efficiency for CO2 formation increases due to the further oxidation of soluble intermediates (formaldehyde and formic acid). At high concentrations of sulfuric acid, the electrooxidation of methanol was suppressed; both the oxidative current and the current efficiency of CO2 decreased, likely due to sulfate/bisulfate adsorption.

Electrocatalytic performance of fuel oxidation by Pt3Ti nanoparticles

A Pt-based electrocatalyst for direct fuel cells, Pt3Ti, has been prepared in the form of nanoparticles. Pt(1,5-cyclooctadiene)Cl2 and Ti(tetrahydrofuran)2Cl4 are reduced by sodium naphthalide in tetrahydrofuran to form atomically disordered Pt3Ti nanoparticles (FCC-type structure: Fm3m; a = 0.39 nm; particle size = 3 +/- 0.4 nm). These atomically disordered Pt3Ti nanoparticles are transformed to larger atomically ordered Pt3Ti nanoparticles (Cu3Au-type structure: Pm3m; a = 0.3898 nm; particle size = 37 +/- 23 nm) by annealing above 400 degrees C. Both atomically disordered and ordered Pt3Ti nanoparticles show lower onset potentials for the oxidation of formic acid and methanol than either pure Pt or Pt-Ru nanoparticles. Both atomically disordered and ordered Pt3Ti nanoparticles show a much lower affinity for CO adsorption than either pure Pt or Pt-Ru nanoparticles. Atomically ordered Pt3Ti nanoparticles show higher oxidation current densities for both formic acid and methanol than pure Pt, Pt-Ru, or atomically disordered Pt3Ti nanoparticles. Pt3Ti nanoparticles, in particular the atomically ordered materials, have promise as anode catalysts for direct fuel cells.