Search

Li-rich rocksalt oxides are promising candidates as high-energy density cathode materials for next-generation Li-ion batteries because they present extremely diverse structures and compositions. Most reported materials in this family contain as many cations as anions, a characteristic of the ideal cubic closed-packed rocksalt composition. In this work, a new rocksalt-derived structure type is stabilized by selecting divalent Cu and pentavalent Sb cations to favor the formation of oxygen vacancies during synthesis. The structure and composition of the oxygen-deficient Li4CuSbO5.5□0.5 phase is characterized by combining X-ray and neutron diffraction, ICP-OES, XAS, and magnetometry measurements. The ordering of cations and oxygen vacancies is discussed in comparison with the related Li2CuO2□1 and Li5SbO5□1 phases. The electrochemical properties of this material are presented, with only 0.55 Li+ extracted upon oxidation, corresponding to a limited utilization of cationic and/or anionic redox, whereas more than 2 Li+ ions can be reversibly inserted upon reduction to 1 V vs Li+/Li, a large capacity attributed to a conversion reaction and the reduction of Cu2+ to Cu0. Control of the formation of oxygen vacancies in Li-rich rocksalt oxides by selecting appropriate cations and synthesis conditions affords a new route for tuning the electrochemical properties of cathode materials for Li-ion batteries. Furthermore, the development of material models of the required level of detail to predict phase diagrams and electrochemical properties, including oxygen release in Li-rich rocksalt oxides, still relies on the accurate prediction of crystal structures. Experimental identification of new accessible structure types stabilized by oxygen vacancies represents a valuable step forward in the development of predictive models., Controlling the composition and synthesis conditions of Li-rich rocksalt oxides can lead to to new structure types stabilized by oxygen vacancies. The complex atomic ordering of Li4CuSbO5.5 is described and discussed in the context of other oxygen-deficient rocksalt oxides.

A newly reported compound, CuAgBiI5, is synthesized as powder, crystals, and thin films. The structure consists of a 3D octahedral Ag+/Bi3+ network as in spinel, but occupancy of the tetrahedral interstitials by Cu+ differs from those in spinel. The 3D octahedral network of CuAgBiI5 allows us to identify a relationship between octahedral site occupancy (composition) and octahedral motif (structure) across the whole CuI-AgI-BiI3 phase field, giving the ability to chemically control structural dimensionality. To investigate composition-structure-property relationships, we compare the basic optoelectronic properties of CuAgBiI5 with those of Cu2AgBiI6 (which has a 2D octahedral network) and reveal a surprisingly low sensitivity to the dimensionality of the octahedral network. The absorption onset of CuAgBiI5 (2.02 eV) barely changes compared with that of Cu2AgBiI6 (2.06 eV) indicating no obvious signs of an increase in charge confinement. Such behavior contrasts with that for lead halide perovskites which show clear confinement effects upon lowering dimensionality of the octahedral network from 3D to 2D. Changes in photoluminescence spectra and lifetimes between the two compounds mostly derive from the difference in extrinsic defect densities rather than intrinsic effects. While both materials show good stability, bulk CuAgBiI5 powder samples are found to be more sensitive to degradation under solar irradiation compared to Cu2AgBiI6.

We report a new polymorph of lithium aluminum pyrophosphate, LiAlP2O7, discovered through a computationally guided synthetic exploration of the Li-Mg-Al-P-O phase field. The new polymorph formed at 973 K, and the crystal structure, solved by single-crystal X-ray diffraction, adopts the orthorhombic space group Cmcm with a = 5.1140(9) A, b = 8.2042(13) A, c = 11.565(3) A, and V = 485.22(17) A3. It has a three-dimensional framework structure that is different from that found in other LiMIIIP2O7 materials. It transforms to the known monoclinic form (space group P21) above ∼1023 K. Density functional theory (DFT) calculations show that the new polymorph is the most stable low-temperature structure for this composition among the seven known structure types in the AIMIIIP2O7 (A = alkali metal) families. Although the bulk Li-ion conductivity is low, as determined from alternating-current impedance spectroscopy and variable-temperature static 7Li NMR spectra, a detailed analysis of the topologies of all seven structure types through bond-valence-sum mapping suggests a potential avenue for enhancing the conductivity. The new polymorph exhibits long (>4 A) Li-Li distances, no Li vacancies, and an absence of Li pathways in the c direction, features that could contribute to the observed low Li-ion conductivity. In contrast, we found favorable Li-site topologies that could support long-range Li migration for two structure types with modest DFT total energies relative to the new polymorph. These promising structure types could possibly be accessed from innovative doping of the new polymorph.

Multinary lithium oxides with the rock salt structure are of technological importance as cathode materials in rechargeable lithium ion batteries. Current state-of-the-art cathodes such as LiNi1/3Mn1/3Co1/3O2 rely on redox cycling of earth-abundant transition-metal cations to provide charge capacity. Recently, the possibility of using the oxide anion as a redox center in Li-rich rock salt oxides has been established as a new paradigm in the design of cathode materials with enhanced capacities (>200 mAh/g). To increase the lithium content and access electrons from oxygen-derived states, these materials typically require transition metals in high oxidation states, which can be easily achieved using d0 cations. However, Li-rich rock salt oxides with high valent d0 cations such as Nb5+ and Mo6+ show strikingly high voltage hysteresis between charge and discharge, the origin of which is uninvestigated. In this work, we study a series of Li-rich compounds, Li4+ xNi1- xWO6 (0 ≤ x ≤ 0.25) adopting two new and distinct cation-ordered variants of the rock salt structure. The Li4.15Ni0.85WO6 (x = 0.15) phase has a large reversible capacity of 200 mAh/g, without accessing the Ni3+/Ni4+ redox couple, implying that more than two-thirds of the capacity is due to anionic redox, with good cyclability. The presence of the 5d0 W6+ cation affords extensive (>2 V) voltage hysteresis associated with the anionic redox. We present experimental evidence for the formation of strongly stabilized localized O-O single bonds that explain the energy penalty required to reduce the material upon discharge. The high valent d0 cation associates localized anion-anion bonding with the anion redox capacity.

The products of the solid-state reactions between potassium metal and tetracene (K:Tetracene, 1:1, 1.5:1, and 2:1) are fully structurally characterized. Synchrotron X-ray powder diffraction shows that only K2Tetracene forms under the reaction conditions studied, with unreacted tetracene always present for x < 2. Diffraction and 13C MAS NMR show that K2Tetracene has a crystal structure that is analogous to that of K2Pentacene, but with the cations ordered on two sites because of the influence of the length of the hydrocarbon on possible cation positions. K2Tetracene is a nonmagnetic insulator, thus further questioning the nature of reported superconductivity in this class of materials., Potassium intercalated tetracene, K2Tetracene, is synthesized and its crystal structure solved and refined from powder data. The crystal chemistry of the K2Tetracene phase contrasts clearly with that of the other alkali metal intercalated polyaromatic hydrocarbons structures reported to date in a way that can be directly related to the molecular structure of tetracene in that the cations cannot be disordered due to fewer sites present in the structure compared to other PAHs studied.

Both layered multiple-anion compounds and homologous series are of interest for their electronic properties, including the ability to tune the properties by changing the nature or number of the layers. Here we expand, using both computational and experimental techniques, a recently reported three-anion material, Bi4O4Cu1.7Se2.7Cl0.3, to the homologous series Bi2+2nO2+2nCu2−δSe2+n–δXδ (X = Cl, Br), composed of parent blocks that are well-studied thermoelectric materials. All of the materials show exceptionally low thermal conductivity (0.2 W/mK and lower) parallel to the axis of pressing of the pellets, as well as narrow band gaps (as low as 0.28 eV). Changing the number of layers affects the band gap, thermal conductivity, carrier type, and presence of a phase transition. Furthermore, the way in which the different numbers of layers are accessed, by tuning the compensating Cu vacancy concentration and halide substitution, represents a novel route to homologous series. This homologous series shows tunable ...

We report the syntheses and structures of five metal–organic frameworks (MOFs) based on transition metals (NiII, CuII, and ZnII), adenine, and di-, tri-, and tetra-carboxylate ligands. Adenine, with multiple N donor sites, was found to coordinate to the metal centers in different binding modes including bidentate (through N7 and N9, or N3 and N9) and tridentate (through N3, N7, and N9). Systematic investigations of the protonation states of adenine in each MOF structure via X-ray photoelectron spectroscopy revealed that adenine can be selectively protonated through N1, N3, or N7. The positions of H atoms connected to the N atoms were found from the electron density maps, and further supported by the study of C–N–C bond angles compared to the literature reports. DFT calculations were performed to geometrically optimize and energetically assess the structures simulated with different protonation modes. The present study highlights the rich coordination chemistry of adenine and provides a method for the determination of its protonation states and the location of protonated N atoms of adenine within MOFs, a task that would be challenging in complicated adenine-based MOF structures., The protonation states and positions of hydrogen atoms in five adenine-based metal−organic frameworks were revealed using geometrical studies based on single-crystal XRD data supported by XPS spectra and DFT calculations.

Phonon-glass electron-crystal (PGEC) behaviour is realised in La0.5Na0.5Ti1-xNbxO3 thermoelectric oxides. The vibrational disorder imposed by the presence of both La3+ and Na+ cations on the A site of the ABO(3) perovskite oxide La0.5Na0.5TiO3 produces a phononglass with a thermal conductivity, kappa, 80% lower than that of SrTiO3 at room temperature. Unlike other state-of-the-art thermoelectric oxides, where there is strong coupling of kappa to the electronic power factor, the electronic transport of these materials can be optimised independently of the thermal transport through cation substitution at the octahedral B site. The low kappa of the phonon-glass parent is retained across the La0.5Na0.5Ti1-xNbxO3 series without disrupting the electronic conductivity, affording PGEC behaviour in oxides.

The production of cyclopentanone derivatives from 5-hydroxymethylfurfural (HMF) using non-noble metal based catalysts is reported for the first time. Five different mixed oxides containing Ni, Cu, Co, Zn and Mg phases on an Al-rich amorphous support were prepared and characterised (XRD, ICP, SEM, TEM, H2-TPR, NH3/CO2-TPD and N2 sorption). The synthesised materials resulted in well-dispersed high metal loadings in a mesoporous network, exhibiting acid/base properties. The catalytic performance was tested in a batch stirred reactor under H2 pressure (20–50 bar) in the range T = 140–180 °C. The Cu–Al2O3 and the Co–Al2O3 catalysts showed a highly selective production of 3-hydroxymethylcyclopentanone (HCPN, 86%) and 3-hydroxymethylcyclopentanol (HCPL, 94%), respectively. A plausible reaction mechanism is proposed, clarifying the role of the reduced metal phases and the acid/basic sites on the main conversion pathways. Both Cu–Al2O3 and Co–Al2O3 catalysts showed a loss of activity after the first run, which can be reversed by a regeneration treatment. The results establish an efficient catalytic route for the production of the diol HCPL (reported for the first time) and the ketone HCPN from bio-derived HMF over 3d transition metals based catalysts in an environmental friendly medium such as water.

Investigation of the potential for nanomaterials to generate immunogenic effects is a key aspect of a robust preclinical evaluation. In combination with physicochemical characterization, such assessments also provide context for how material attributes influence biological outcomes. Furthermore, appropriate models for these assessments allow accurate in vitro to in vivo extrapolation, which is vital for the mechanistic understanding of nanomaterial action. Here we have assessed the immunogenic impact of a small panel of commercially available and in-house prepared nanomaterials on primary human peripheral blood mononuclear cells (PBMCs). A diethylaminoethyl-dextran (DEAE-dex) functionalized superparamagnetic iron oxide nanoparticle (SPION) generated detectable quantities of tumor necrosis factor &alpha, (TNF&alpha, ), interleukin-1&beta, (IL-1&beta, ), and IL-10, the only tested material to do so. The human leukemia monocytic cell line THP-1 was used to assess the potential for the nanomaterial panel to affect cellular oxidation-reduction (REDOX) via measurement of reactive oxygen species and reduced glutathione. Negatively charged sulfonate-functionalized polystyrene nanoparticles demonstrated a size-related trend for the inhibition of caspase-1, which was not observed for amine-functionalized polystyrene of similar sizes. Silica nanoparticles (310 nm) resulted in a 93% increase in proliferation compared to the untreated control (p &lt, 0.01). No other nanomaterial treatments resulted in significant change from that of unstimulated PBMCs. Responses to the nanomaterials in the assays described demonstrate the utility of primary cells as ex vivo models for nanomaterial biological impact.

It is challenging to achieve p-type doping of zinc oxides (ZnO), which are of interest as transparent conductors in optoelectronics. A ZnO-related ternary compound, SrZnO2, was investigated as a potential host for p-type conductivity. First-principles investigations were used to select from a range of candidate dopants the substitution of Li+ for Zn2+ as a stable, potentially p-type, doping mechanism in SrZnO2. Subsequently, single-phase bulk samples of a new p-type-doped oxide, SrZn1–xLixO2 (0 < x < 0.06), were prepared. The structural, compositional, and physical properties of both the parent SrZnO2 and SrZn1–xLixO2 were experimentally verified. The band gap of SrZnO2 was calculated using HSE06 at 3.80 eV and experimentally measured at 4.27 eV, which confirmed the optical transparency of the material. Powder X-ray diffraction and inductively coupled plasma analysis were combined to show that single-phase ceramic samples can be accessed in the compositional range x < 0.06. A positive Seebeck coefficient ...

Substitution of La3+ for Ba2+ in LaBaGa3O7 melilite yields a new interstitial-oxide-ion conducting La1+xBa1–xGa3O7+0.5x solid solution, which only extends up to x = 0.35, giving a maximum interstitial oxygen content allowed in La1+xBa1–xGa3O7+0.5x as about half of those allowed in La1+x(Sr/Ca)1–xGa3O7+0.5x. La1.35Ba0.65Ga3O7.175 ceramic displays bulk conductivity ∼1.9 × 10–3 S/cm at 600 °C, which is lower than those of La1.35(Sr/Ca)0.65Ga3O7.175, showing the reduced mobility for the oxygen interstitials in La1+xBa1–xGa3O7+0.5x than in La1+x(Sr/Ca)1–xGa3O7+0.5x. Rietveld analysis of neutron powder diffraction data reveals that the oxygen interstitials in La1.35Ba0.65Ga3O7.175 are located within the pentagonal tunnels at the Ga level between two La/Ba cations along the c-axis and stabilized via incorporating into the bonding environment of a three-linked GaO4 among the five GaO4 tetrahedra forming the pentagonal tunnels, similar to the Sr and Ca counterparts. Both static lattice atomistic simulation and den...

This work was supported by the EPSRC under EP/H000925. K.C.S. grateful acknowledges EU for the Marie Curie Fellowship (300390 NanoBioMOFs FP7-PEOPLE-2011-IEF).

A porphyrin-based metal-organic framework is shown to be structurally stable towards acid loading using either hydrochloric or formic acid. The capacity of this material as an ammonia sorbent was analysed using micro-breakthrough experiments in both dry and humid ammonia flows. The acid loaded material exhibited excellent uptake in comparison with the parent MOF.

Iron (II,III) oxide Fe3O4 nanoparticles (25 and 50 nm NPs) are grafted with amine groups through silanization in order to generate a positively charged coating for binding negatively charged species including DNA molecules. The spatial nature of the coating changes from a 2-D-functionalized surface (monoamines) through a layer of amine oligomers (diethylenetriamine or DETA, about 1 nm in length) to a 3-D layer of polyamine (polyethyleneimine or PEI, thickness ≥3.5 nm). These Fe3O4-PEI NPs were prepared by binding short-chain PEI polymers to the iodopropyl groups grafted on the NP surface. In this work, the surface charge density, or zeta potential, of the nanoparticles is found not to be the only factor influencing the DNA binding capacity, which also seems not to be affected by their buffering capacity profile in the range of pH 4-10. This study also allows the investigation of this 3-D effect on the surface of a nanoparticle as opposed to conventional 2-D amine functionalization. The flexibility of the PEI coating, which consists of only 1, 2, and 3° amines, on the nanoparticle surface has a significant influence on the overall DNA binding capacity and the binding efficiency (or N/P ratio). These polyamine-functionalized nanoparticles can be used in the purification of biomolecules and the delivery of drugs and large biomolecules.

The new Fe(3+) oxide BaFe9LiO15 is isostructural with the magnetically frustrated material BaV10O15, adopting a structure based on the stacking of close-packed pure oxide and BaO7 layers. Neutron diffraction and Mössbauer spectroscopy shows that BaFe9LiO15 is long-range antiferromagnetically ordered with a Néel temperature of 460 K. The magnetic ordering of antiferromagnetically coupled ferromagnetic planes is stabilized by 90° and 180° superexchange interactions between the Fe(3+) cations that supersede the frustrated in-plane direct exchange observed in t(2g)-only systems.

Cobalt and ruthenium-promoted cobalt Fischer–Tropsch catalysts supported on titania have been prepared for the first time by gas anti-solvent precipitation. The use of dense CO2 as an anti-solvent enables the precipitation of cobalt acetate and ruthenium acetylacetonate onto preformed titania. The gas anti-solvent process produces catalysts with the desired 20 wt % cobalt content as precursors, which on calcination give highly dispersed Co3O4. The addition of ruthenium to the gas anti-solvent prepared cobalt catalysts has been investigated by two methods (a) coprecipitation with cobalt acetate and (b) wet impregnation onto a precalcined cobalt titania catalyst, and these resulted in catalysts with distinctly different properties. These catalysts were compared with a standard ruthenium-promoted cobalt catalyst prepared by wet impregnation and were found to be substantially more active for the Fischer–Tropsch reaction.

Exploration of the Ca-Ga-Nb-O phase diagram by solid-state reaction in air led to isolation of Ca4GaNbO8. The crystal structure was determined ab initio by synchrotron X-ray and high-resolution neutron powder diffraction. Ca4GaNbO8 adopts a heavily distorted oxygen-deficient perovskite structure with the rare feature of complete ordering of the three B-site cations, driven by their distinct chemistries. One of the calcium cations occupies a distorted octahedral cavity and together with tetrahedrally coordinated Ga and octahedrally coordinated Nb is considered as a B-site cation in the ABO(3-x) perovskite. This interpretation of the structure reveals Ca4GaNbO8 is part of a family of B-site and vacancy-ordered perovskites related to mineral structures. The anion-vacancy ordering pattern in Ca4GaNbO8 is driven by the coordination preferences of the three structurally distinct cations and correlated with the ordering of each cation on a distinct site. Alternating current impedance spectra show Ca4GaNbO8 is insulating (bulk conductivity 10(-5)-10(-7) S·cm(-1)) over the measured temperature range 550-950 °C with an activation energy of 1.10(3) eV.

Alkali metal intercalation into polyaromatic hydrocarbons (PAHs) has been studied intensely after reports of superconductivity in a number of potassium- and rubidium-intercalated materials. There are, however, no reported crystal structures to inform our understanding of the chemistry and physics because of the complex reactivity of PAHs with strong reducing agents at high temperature. Here we present the synthesis of crystalline K2Pentacene and K2Picene by a solid–solid insertion protocol that uses potassium hydride as a redox-controlled reducing agent to access the PAH dianions, and so enables the determination of their crystal structures. In both cases, the inserted cations expand the parent herringbone packings by reorienting the molecular anions to create multiple potassium sites within initially dense molecular layers, and thus interact with the PAH anion π systems. The synthetic and crystal chemistry of alkali metal intercalation into PAHs differs from that into fullerenes and graphite, in which the cation sites are pre-defined by the host structure.

We present the synthesis and structural characterisation of a transition metal oxide hydride, LaSrCoO_3H_{0.7}, which adopts an unprecedented structure in which oxide chains are bridged by hydride anions to form a two- dimensional extended network. The metal centers are strongly coupled by their bonding with both oxide and hydride ligands to produce magnetic ordering up to at least 350 K. The synthetic route is sufficiently general to allow the prediction of a new class of transition metal-containing electronic and magnetic materials., Comment: 6 pages, including 3 figures

The room-temperature crystal structure of the brownmillerite SrCaMnGaO5+δ (δ = 0.035) has been refined from neutron powder diffraction data; space group Ima2, a = 15.7817(6), b = 5.4925(2), c = 5.3196(2) Å. Mn and Ga occupy 99.0(2)% of the 6- and 4-coordinate sites, respectively. A combination of magnetometry, neutron diffraction and μSR spectroscopy has shown that the compound orders magnetically at 180 K, and that the low-temperature phase has a G-type antiferromagnetic structure, with an ordered magnetic moment of 3.30(2) μB per Mn at 2 K. Displaced hysteresis loops provide evidence that the atomic moment has an additional, glassy component. Magnetometry shows that significant short-range magnetic interactions persist above 180 K, and μSR that the spin fluctuations are thermally activated in this temperature region. The compound is an electrical insulator which at 159 K shows an unusually large magnetoresistance of 85% in 6T, increasing to 90% in 13 T. © 2002 Elsevier Science (USA).

The capability of sodium hydride as a reducing agent in oxide deintercalation reactions is explored. The Ni(III) perovskite LaNiO3 can be reduced topotactically to LaNiO2, isostructural with the 'infinite layer' cuprates, using solid sodium hydride in a sealed evacuated tube at 190 ≤ T/°C ≤ 210, and a similar infinite-layer phase is prepared by reduction of NdNiO3. Structural characterization indicates the coexistence of incompletely reduced regions, with five-coordinate Ni centers due to the introduction of oxide anions between the NiO23- sheets, giving samples with a refined stoichiometry of LaNiO(2.025(3)). Neutron powder diffraction and magnetization measurements indicate that the lamellar Ni(I) phase does not show the long-range antiferromagnetic ordering characteristic of isoelectronic Cu(II) oxides. This may be due either to the influence of the interlamellar oxide defect regions or to the reduced covalent mixing of Ni 3d and O 2p levels.

Neutron and synchrotron X-ray powder diffraction techniques have been used to refine the crystal and magnetic structures of the n = 2 Ruddlesden-Popper (RP) system Sr2LaMn2O7. The sample is shown to be biphasic, although both phases are of the RP type and have similar structural parameters. The majority phase (81%) adopts a collinear antiferromagnetic structure below â?¼210 K whereas the minority phase is ferromagnetically ordered below â?¼125 K. The ordered magnetic moments lie in the xy plane in both phases. The behavior observed is discussed in terms of the interplay between structural and electronic factors. Comparison with data obtained previously by other workers leads to the conclusion that our results have some general significance in the study of n = 2 RP systems.

The perovskite- and K2NiF4-structure group 5 oxynitrides SrTaO2N, BaTaO2N, Sr2TaO3N, and Ba2TaO3N, previously prepared by reacting oxide precursors with ammonia, may also be prepared by the reaction between the appropriate alkaline earth oxide and TaON at 1500°C under 1 atm of pure nitrogen gas for a few hours. The nitrogen atmosphere is essential to prevent reduction of TaV, and the method of inductive heating ensures that the nitrogen atmosphere above the sample is maintained free of oxygen or water. SrTaO2N crystallizes in I4/mcm with a = 5.694 11(7) Å, b = 8.0658(2) Å, and Z = 4. The oxide and nitride anions are almost completely disordered, as observed when the material is made by nitridation of a pure oxide precursor using ammonia at 900-1000°C, but contrasting with the full O/N order observed when such nitridation is mineralizer assisted. The detailed structure of Ba2TaO3N is reported for the first time: this compound adopts the K2NiF4 type structure with full O/N order in space group I4/mmm with a = 4.115 08(3) Å, c = 13.3778(1) Å, and Z = 2 and is isostructural with the strontium analogue (Sr2TaO3N: I4/mmm, a = 4.038 99(4) Å, c = 12.6007(3) Å, and Z = 2). O/N disorder is favored in perovskite-structure oxynitrides, but in layered K2NiF4-structure materials O/N ordering is the norm, with the ordering scheme dictated by the competition between cations of differing electronegativity for the anions.

The new reduced K2NiF4 Co(II) phase, LaSrCoO(3.5-x), is prepared by reduction of the Co(III) containing LaSrCoO4 using H2 gas and the new hydride solid-solid reduction methods. The hydride route is superior in both crystallinity and control of phase purity and allows access to reduced phases containing substantial concentrations of Co(I). The anion vacancies are located within the MO2 planes of the K2NiF4 structure but do not prevent the onset of long-range antiferromagnetic order: the magnetic structure is refined using a noncollinear model consistent with the tetragonal crystal symmetry.

Polycrystalline samples of bilayered brownmillerite-like Ca 2.5Sr0.5GaCo0.15Mn1.85O8 and Ca2.5Sr0.5Ga1.2Mn1.8O 8 have been prepared and characterised by magnetometry and neutron diffraction over a wide temperature range. The structural chemistry and magnetic properties are compared to those of Ca2.5Sr0.5GaMn 2O8. Ga enrichment has a significant effect on the former but not on the latter, whereas changes in both occur when paramagnetic Co 3+ cations enter the parent phase on the 4-coordinate sites. The coupling between the environment around the 4-coordinate cations and the transition to an antiferromagnetic ordered state that was observed in Ca 2.5Sr0.5GaMn2O8 is not apparent in the cation-substituted compositions, although both show long-range antiferromagnetic order at low temperatures. © 2005 Elsevier Inc. All rights reserved.

High resolution transmission electron microscopy has been used to probe the microstructure of the n = 2 Ruddlesden-Popper manganates Sr{sub 2}LnMn{sub 2}O{sub 7} (Ln = Y, La, Nd, Eu, Ho). Intergrowths of n = 1 (K{sub 2}NiF{sub 4}) are observed only for Ln = La. Intergrowths with n {ge} 5, essentially perovskite microdomains, are seen in the other compositions. The density of perovskite regions is greatest near the edges of the thin specimens, with the n = 2 structure becoming established in the bulk. The complementarity of HRTEM and neutron diffraction is discussed.

Metal–Organic Frameworks (MOFs) are porous crystalline materials that have emerged as promising hosts\ud for the heterogenization of homogeneous organometallic catalysts, forming hybrid materials which\ud combine the benefits of both classes of catalysts. Herein, we report the encapsulation of the\ud organometallic cationic Lewis acidic catalyst [CpFe(CO)2(L)]+ ([Fp–L]+, Cp ¼ h5\ud -C5H5, L ¼ weakly bound\ud solvent) inside the pores of the anionic [Et4N]3[In3(BTC)4] MOF (H3BTC ¼ benzenetricarboxylic acid) via\ud a direct one-step cation exchange process. To conclusively validate this methodology, initially [Cp2Co]+\ud was used as an inert spatial probe to (i) test the stability of the selected host; (ii) monitor the\ud stoichiometry of the cation exchange process and (iii) assess pore dimensions, spatial location of the\ud cationic species and guest-accessible space by single crystal X-ray crystallography. Subsequently,\ud the quasi-isosteric [Fp–L]+ was encapsulated inside the pores via partial cation exchange to form\ud [(Fp–L)0.6(Et4N)2.4][In3(BTC)4]. The latter was rigorously characterized and benchmarked as\ud a heterogeneous catalyst in a simple Diels–Alder reaction, thus verifying the integrity and reactivity of\ud the encapsulated molecular catalyst. These results provide a platform for the development of\ud heterogeneous catalysts with chemically and spatially well-defined catalytic sites by direct exchange\ud of cationic catalysts into anionic MOFs.

Gold and gold alloys, in the form of supported nanoparticles, have been shown over the last three decades to be highly effective oxidation catalysts. Mixed metal oxide perovskites, with their high structural tolerance, are ideal for investigating how changes in the chemical composition of supports affect the catalysts' properties, while retaining similar surface areas, morphologies and metal co-ordinations. However, a significant disadvantage of using perovskites as supports is their high crystallinity and small surface area. We report the use of a supercritical carbon dioxide anti-solvent precipitation methodology to prepare large surface area lanthanum based perovskites, making the deposition of 1 wt% AuPt nanoparticles feasible. These catalysts were used for the selective oxidation of glycerol. By changing the elemental composition of the perovskite B site, we dramatically altered the reaction pathway between a sequential oxidation route to glyceric or tartronic acid and a dehydration reaction pathway to lactic acid. Selectivity profiles were correlated to reported oxygen adsorption capacities of the perovskite supports and also to changes in the AuPt nanoparticle morphologies. Extended time on line analysis using the best oxidation catalyst (AuPt/LaMnO3) produced an exceptionally high tartronic acid yield. LaMnO3 produced from alternative preparation methods was found to have lower activities, but gave comparable selectivity profiles to that produced using the supercritical carbon dioxide anti-solvent precipitation methodology.

The coordination of benzene-1,3,5-tribenzoate (BTB) and imidazole (Im) with cobalt under basic conditions yields a 2D layered structure, Co 3 (BTB) 1.5 (Im) 1.35 (O) 0.5 (OH) 0.5 (H 2 O) 1.65 guests ( 1 ), in which the imidazoles are weakly π–π stacked and hydrogen bonded to the adjacent layers affording a 3D supramolecular network. The structure is based on a hexanuclear Co 6 building unit which comprises four octahedral and two tetrahedral Co(II) centres. The framework is permanently porous to N 2 , CO 2 and CH 4 , with the strength of interaction at zero coverage being comparable to that at high loading.

BACKGROUND: This research investigated the effect of platinum (Pt) on the reactivity of tungsten oxide (WO3) for the visible light photocatalytic oxidation of dyes. RESULTS: Nanocrystalline tungsten oxide (WO3) photocatalysts were synthesised by a sol-gel process and employed for the photocatalytic degradation of Methyl Orange under visible light. For comparison commercial bulk WO3 materials were also studied for the same reaction. These materials were fully characterised using X-ray diffraction (XRD), UV-visible diffuse reflection spectroscopy and transmission electron microscopy (TEM). The photocatalytic oxidation of iso-propanol was used as a model reaction to follow the concomitant reduction of molecular oxygen. No reactions occured in the absence of platinum, which is an essential co-catalyst for the multi-electron reduction of oxygen. The platinised WO3 catalysts were stable for multiple oxidation–reduction cycles. The results from the catalytic activity measurements showed that platinised nanocrystalline WO3 is a superior oxidation photocatalyst when compared with bulk WO3. Methyl Orange was completely decolourised in 4 h. CONCLUSIONS: The enhanced performance of nanocrystalline Pt-WO3 is attributed to improved charge separation in the nanosized photocatalyst. Platinum is an essential co-catalyst to reduce oxygen. This photocatalyst could be applied to the treatment of organic pollutants in wastewater, with the advantage of using visible light compared with the widely studied TiO2, which requires UV light. Copyright © 2011 Society of Chemical Industry

Supercritical CO2 is used as an antisolvent to precipitate out nanostructured homogeneous mixtures of Cu2+ and Mn3+ with crystallites of 10–20 nm in diameter. Following calcination, this material forms a crystalline tetragonal spinel, CuMn2O4, with a branched chainlike structure with a length of 160–200nm and diameters of approximately 40nm. This new material is more than twice as active per unit surface area as the conventionally prepared hopcalite catalysts for the oxidation of carbon monoxide. This is the first time that homogeneous mixed oxides have been formed using this method.

The thermal evolution of the crystal structure of PrSr3Co1.5Fe1.5O10–d , a member of the n = 3 family of Ruddlesden-Popper compounds, has been studied by means of variable temperature synchrotron X-ray powder diffraction combined with room temperature neutron diffraction studies. This structure takes the ideal tetragonal I4/mmm (n°139) space group. The possibility of symmetry lowering to the Pbca (n°61) space group by slight tilting and rotation of the oxygen atoms around the octahedral B site is discussed. The non linear thermal expansion of the compound in air is caused by a chemical expansion accompanying the loss of oxygen that comes in addition to normal thermal expansion. A mechanism describing the creation of oxygen vacancies is proposed.

The manufacture of heterogeneous catalysts and catalyst supports produces substantial amounts of nitrate containing aqueous effluent. The use of nitrate free precursors and an environmentally friendly process would change the manufacture so that the entire process of catalyst synthesis and use can be considered green. In this work the precipitation of titania acetylacetonate nanoparticles for use as catalytic supports using a supercritical carbon dioxide anti-solvent process was investigated over a range of conditions. The effects of 1) pressure, 2) temperature, 3) solution flowrate, 4) solution concentration of TiO(acac) 2 in methanol, 5) nozzle diameter and 6) CO 2 /methanol flow ratio on the mean particle size and morphology were studied. Particle sizes between 27 and 78 nm were obtained and were generally string and branch-like with an amorphous nature. Pressure and temperature had little effect on the mean particle size. A decrease in the velocity of the solution flow rate led to an increase in mean particle size and to particles that exhibited greater interconnectivity. It was also observed that an increase in concentration of TiO(acac) 2 in methanol led to an increase in mean particle size. The process shows promise for the production of catalysts by an environmentally acceptable route.

A method for the in situ preparation of Pt nanoparticles of controlled size based on the modification of highly oriented pyrolytic graphite (HOPG) with aminophenyl groups employing diazonium chemistry is demonstrated. It is shown that full chemical reduction of an Ar–NO2 grafted surface is achieved with aqueous Sn(II). The formation of aminophenyl groups was established by chemical reaction with 1,2-benzoquinone followed by electrochemical detection of the bound quinone using square wave voltammetry. The oxidation state of nitrogen was confirmed by XPS. Platinum nanoparticles were prepared chemically by the attachment of Pt(II) on the Ar–NH2 modified electrodes followed by reduction with NaBH4. This resulted in the formation of Pt nuclei that could be further grown. The surfaces formed were characterized by TEM, XRD and XPS. The dependence on particle size of the electro-oxidation of CO and methanol in 0.5 M H2SO4 was studied for three different nanoparticle sizes, 2.0, 2.7 and 4.0 nm. It is demonstrated that reactivity for these reactions decreases with decreasing particle size. The difficulties in comparing particle sizes calculated from XRD data with those from TEM are discussed.

A2B2O7 complex oxides with the pyrochlore structure feature a wide variety of chemical compositions and corresponding diverse electrical and physical properties. A new pyrochlore, Yb0.96Ca1.04TiNbO6.98, is reported and characterized in terms of structural stability and electrical properties. The material is stable to ∼1450 °C in 5% H2/N2 and has a high electronic conductivity in a reducing atmosphere, e.g., 9 S/cm at 800 °C in 5% H2/N2 after high-temperature reduction. Other cation substitutions enhance the low-temperature kinetics of conductivity response to changes in oxygen partial pressure.

A new six-layer perovskite-related structure Ba 6Na 2Nb 2M 2O 17 (M = P, V), which consists of cubic (c) BaO 3 layers and oxygen-deficient pseudocubic (c') BaO 2 layers stacked in the sequence c'ccccc, is presented. In Ba 6Na 2Nb 2M 2O 17, two-dimensional slabs of the well-known 2:1 octahedral cation-ordered perovskite motif are isolated between layers of tetrahedral units formed by anion vacancy ordering: two consecutive NbO 6 octahedral layers are sandwiched by two single NaO 6 octahedral layers, which, in turn, connect with two isolated MO 4 tetrahedral layers. Both oxides are derived from the 2:1 ordered perovskite structure (e.g., Ba 3ZnTa 2O 9) by ordered removal of O atoms in every sixth BaO 3 layer. Both materials exhibit a relative permittivity of approximately 20-23, Q x f 0 values of approximately 7800-10600 GHz, and negative temperature coefficients of the resonant frequency of approximately -23 to -7 ppm/ degrees C.

Reaction of L-cysteine with M(NO3)2 x xH2O (M = Cd, Zn) generates M(L-cysteinate), which feature one-dimensional substructures that can be viewed as fragments of bulk structures of CdS (rock salt high pressure phase) and ZnS (wurtzite) because of the bridging modes accessible to the sulfur atom of L-cysteine. The MS substructures are arranged in a regular and periodic fashion within the crystal via the carboxylate function of L-cysteine. Considering the structural similarities with bulk materials, the optical properties of M(L-cysteinate) were studied and indicate blue shifts of the band gap of 2.59 eV (M = Cd, compared to CdS rock salt) and 1.37 eV (M = Zn, compared to ZnS wurtzite) with respect to the bulk MS structures, due to the low dimensionality of the metal-sulfur arrangement. The chelating nature of the cysteine ligand imposes an unusual mer arrangement of three binding S moieties at Cd with a correspondingly high Cd coordination number in a chalcogenide-based material. Density of states calculations show strong electronic structure similarities with the bulk phases and rationalize the band gap changes.

Methane storage is important for the development of alternative energy carriers. The synthesis and methane storage properties of microporous hypercrosslinked organic polymers are reported. The figure shows a simulation of methane sorption in microporous hypercrosslinked poly(p-dichloroxylene); up to 5.2 mmol g(-1]) CH4 at 20 bar/298 K; isosteric heat of sorption similar to 21 kJ mol(-1).

High-conductivity oxide ion electrolytes are needed to reduce the operating temperature of solid-oxide fuel cells. Oxide mobility in solids is associated with defects. Although anion vacancies are the charge carriers in most cases, excess (interstitial) oxide anions give high conductivities in isolated polyhedral anion structures such as the apatites. The development of new families of interstitial oxide conductors with less restrictive structural constraints requires an understanding of the mechanisms enabling both incorporation and mobility of the excess oxide. Here, we show how the two-dimensionally connected tetrahedral gallium oxide network in the melilite structure La1.54Sr0.46Ga3O7.27 stabilizes oxygen interstitials by local relaxation around them, affording an oxide ion conductivity of 0.02–0.1 S cm−1 over the 600–900 ∘C temperature range. Polyhedral frameworks with central elements exhibiting variable coordination number can have the flexibility needed to accommodate mobile interstitial oxide ions if non-bridging oxides are present to favour cooperative network distortions. Fast-ion conductors are needed to reduce the operating temperature of solid-oxide fuel cells. The identification of the conduction mechanism in electrolytes where conduction is based on mobile oxygen interstitials rather than the usual anion vacancies offers a generic design principle for novel solid electrolytes.

The cation ordering in the fluorite-like transparent conductors In{sub 4+} {sub x} Sn{sub 3-2} {sub x} Sb {sub x} O{sub 12} and In{sub 6}TeO{sub 12}, was investigated by Time of Flight Neutron Powder Diffraction and X-ray Powder Diffraction (tellurate). The structural results including atomic positions, cation distributions, metal-oxygen distances and metal-oxygen-metal angles point to a progressive cation ordering on both sites of the Tb{sub 7}O{sub 12}-type structure with a strong preference of the smaller 4d {sup 10} cations (Sn{sup 4+}, Sb{sup 5+}, Te{sup 6+}) for the octahedral sites. The corresponding increase of the overall structure-bonding anisotropy is analyzed in terms of the crystal chemical properties of the OM {sub 4} tetrahedral network of the antistructure. The relationships between the M {sub 7}O{sub 12} and the M {sub 2}O{sub 3} bixbyite-type structures are explored. Within the whole series of compositions In{sub 4+} {sub x}M {sub 3-} {sub x} O{sub 12} (M=Sn, Sb, Te) there exists an increase of the symmetry gap between the more symmetrical bixbyite structure and the M {sub 7}O{sub 12} type. This is tentatively correlated with the progressive weakening of thermal stability of these compositions from Sn to Te via Sb. - Graphical abstract: Hexagonal cell of themore » fluorite-like oxygen-deficient M {sub 7}O{sub 12} structure: symmetrical octahedra and distorted sevenfold-coordinated polyhedra are shown.« less

Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable—and hence little known and largely ignored1—georgeite. The first three of these minerals are widely used as catalyst precursors2, 3, 4 for the industrially important methanol-synthesis and low-temperature water–gas shift (LTS) reactions5, 6, 7, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase2, 3, 8, 9, 10 is usually zincian malachite. This is prepared by a co-precipitation method that involves the transient formation of georgeite11; with few exceptions12 it uses sodium carbonate as the carbonate source, but this also introduces sodium ions—a potential catalyst poison. Here we show that supercritical antisolvent (SAS) precipitation using carbon dioxide (refs 13, 14), a process that exploits the high diffusion rates and solvation power of supercritical carbon dioxide to rapidly expand and supersaturate solutions, can be used to prepare copper/zinc hydroxycarbonate precursors with low sodium content. These include stable georgeite, which we find to be a precursor to highly active methanol-synthesis and superior LTS catalysts. Our findings highlight the value of advanced synthesis methods in accessing unusual mineral phases, and show that there is room for exploring improvements to established industrial catalysts.

Reaction of iron(IIII)chloride with the free base tetrakis(4-carboxyphenyl)porphyrin (H2TCPP) in the presence of different bases leads to the formation of a series of iron/porphyrin metal–organic frameworks. Such a crystal engineering approach led to the obtaining of four structures presenting three different topologies and inorganic secondary building units. Depending on the synthesis conditions, isolated FeIII octahedra, diiron(II) paddle wheel dimers, or extended [FeIII(OH)O4]n chains could be obtained in a controlled manner. The influence of the synthetic conditions on the final structure and the oxidation state of iron is discussed. Stability of the porous solids towards air and water is studied, and their intrinsic porosity is assessed.

A stable visible-light driven photocatalyst (λ ≥ 450 nm) for H2O oxidation is prepared by Rh substitution into the pyrochlore Y2Ti2O7 to a maximum level of 2% by stoichiometric solid state reactions of Y2O3, TiO2, and Rh2O3 under air (Pt foil lined alumina boat, 1300 °C, 2 d).

In situ methods are ideally suited to study the development of property-critical structural features during material processing. As an example of their potential in the area of complex oxide electroceramics, here, we apply X-ray synchrotron and neutron powder diffraction to investigate the ordering processes responsible for optimizing the microwave dielectric properties of the commercial electroceramic barium zinc tantalate (BZT) doped with strontium gallate. The collection of synchrotron diffraction data with high resolution and high intensity during processing has allowed the development of cation site order and growth of ordered domains to be followed during the multi-stage thermal treatment processing used by industry. Complementary neutron diffraction data reveal changes in the cation–oxygen bonding associated with development of the cation-ordered trigonal perovskite structure. The effects of material loss with processing at temperatures of up to 1525°C are discussed following experiments using open and closed systems. The complex nature of the ordering is confirmed by the coexistence of two BZT phases and the formation of a further zinc-deficient phase. The implications of these observations and relation to the industrial processing procedures are discussed.

Desolvation of Ni(2)(4,4'-bipyridine)(3)(NO(3))(4).2CH(3)OH and Ni(2)(4,4'-bipyridine)(3)(NO(3))(4).2C(2)H(5)OH give flexible metal-organic porous structures M and E, respectively, which have the same stoichiometry, but subtly different structures. This study combines measurements of the thermodynamics and kinetics of carbon dioxide, methanol, and ethanol sorption on adsorbents M and E over a range of temperatures with adsorbent structural characterization at different adsorbate (guest) loadings. The adsorption kinetics for methanol and ethanol adsorption on porous structure E obey a linear driving force (LDF) mass transfer model for adsorption at low surface coverage. The corresponding adsorption kinetics for porous structure M follow a double exponential (DE) model, which is consistent with two different barriers for diffusion through the windows and along the pores in the structure. The former is a high-energy barrier due to the opening of the windows in the structure, required to allow adsorption to occur, while the latter is a lower-energy barrier for diffusion in the pore cavities. X-ray diffraction studies at various methanol and ethanol loadings showed that the host porous structures E and M underwent different scissoring motions, leading to an increase in unit cell volume with the space group remaining unchanged during adsorption. The results are discussed in terms of reversible adsorbate/adsorbent (host/guest) structural changes and the adsorption mechanism involving hydrogen-bonding interactions with specific surface sites for methanol and ethanol adsorption in relation to pore size and extent of filling. This paper contains the first evidence for individual kinetic barriers to diffusion through windows and pore cavities in flexible porous coordination polymer frameworks.

The defect fluorite Zr4O5N2 is presented. A simple layered intergrowth of the important bixbyite and fluorite structure types, it displays an A4X7 vacancy ordering alternative to that in the pyrochlore and other structures. This ordering is stabilized by proximity of the highly charged N3- anions to the bixbyite-type face diagonal vacancy neighbors in the initially cubic cation coordination environment of fluorite. The existence of this simple structure demonstrates the potential of substitution on the anion sublattice to control the structures of ionic defect systems.

Two fullerides derived from Na 2 C 60 by ammonia coordination to the counterions are presented. Both structures adopt body-centered cubic-related anion packings. The sodium cations are extensively disordered in one phase, but their positional ordering in the second phase is correlated with the development of two distinct fulleride anion environments. Electrostatic considerations indicate that the two crystallographically distinct fulleride anions display charge separation.

The control of the interpenetration and chirality of a family of metal-organic frameworks is discussed. These systems contain two- (A) and four-fold (B) interpenetration of helical three-connected networks generated by binding the 1,3,5-benzenetricarboxylate (btc) ligand to a metal center. These frameworks have the general formula Ni(3)(btc)(2)X(m)Y(n).solvent (where X = pyridine or 4-picoline, Y = ethylene glycol, 1,2-propanediol, 1,4-butanediol, meso-2,3-butanediol, 1,2,6-hexanetriol, glycerol). The structural and chemical effects of modifying the alcohol and aromatic amine ligands bound to the metal center include controlling the thermal stability and the degree of interpenetration. Covalent linking of the four interpenetrating networks in the A family and the switching of diol binding from mono- to bidentate are demonstrated. Recognition of chiral diols by the hand of the network helices is investigated by binding an alcohol ligand with two chiral centers of opposite sense to the same helix. This reveals the subtle nature of the helix-ligand interaction.