Counting the Acid Sites in a Commercial ZSM-5 Zeolite Catalyst.

This work investigates the acid sites in a commercial ZSM-5 zeolite catalyst by a combination of spectroscopic and physical methods. The Brønsted acid sites in such catalysts are associated with the aluminum substituted into the zeolite lattice, which may not be identical to the total aluminum content of the zeolite. Inelastic neutron scattering spectroscopy (INS) directly quantifies the concentrations of Brønsted acid protons, silanol groups, and hydroxyl groups associated with extra-framework aluminum species. The INS measurements show that ∼50% of the total aluminum content of this particular zeolite is extra framework, a conclusion supported by solid-state NMR and ammonia temperature-programmed desorption (TPD) measurements. Evidence for the presence of extra-framework aluminum oxide species is also seen in neutron powder diffraction data from proton- and deuterium-exchanged samples. The differences between results from the different analytical methods are discussed, and the novelty of direct proton counting by INS in this typical commercial catalyst is emphasized.

Proton and Oxide Ion Conductivity in Palmierite Oxides.

Solid proton and oxide ion conductors have key applications in several hydrogen-based and energy-related technologies. Here, we report on the discovery of significant proton and oxide ion conductivity in palmierite oxides A3V2O8 (A = Sr, Ba), which crystallize with a framework of isolated tetrahedral VO4 units. We show that these systems present prevalent ionic conduction, with a large protonic component under humidified air (t H ∼ 0.6-0.8) and high protonic mobility. In particular, the proton conductivity of Sr3V2O8 is 1.0 × 10-4 S cm-1 at 600 °C, competitive with the best proton conductors constituted by isolated tetrahedral units. Simulations show that the three-dimensional ionic transport is vacancy-driven and facilitated by rotational motion of the VO4 units, which can stabilize oxygen defects via formation of V2O7 dimers. Our findings demonstrate that palmierite oxides are a new promising class of ionic conductors where stabilization of parallel vacancy and interstitial defects can enable high ionic conductivity.

Hexagonal perovskite derivatives: a new direction in the design of oxide ion conducting materials.

Various structural families have been reported to support oxide ion conductivity; among these, perovskite conductors have received particular attention. The perovskite structure is generally composed of a framework of corner-sharing octahedral units. When the octahedral units share their faces, hexagonal perovskites are formed. Mixed combinations of corner-sharing and face-sharing octahedral units can give rise to a variety of hexagonal perovskite derivatives. However, the ionic conducting properties of these materials have not been well explored. In this feature article, we review the conducting properties of the most significant hexagonal perovskite derivatives, with special focus on Ba3MM'O8.5. Ba3MM'O8.5 is the first hexagonal perovskite derivative to exhibit substantial oxide ion conductivity, and here we outline the structural features that are key for the oxide ion conduction within this system. The results demonstrate that further investigation of hexagonal perovskite derivatives could open up new directions in the design of oxide ion conductors.

Relationship between the Crystal Structure and Electrical Properties of Oxide Ion Conducting Ba3W1.2Nb0.8O8.6.

The oxide ionic conductor Ba3W1.2Nb0.8O8.6 has been synthesized as part of an investigation into the new class of Ba3M'M''O8.5 (M' = W, Mo; M'' = Nb) oxide-ion conducting hexagonal perovskite derivatives. The substitution of W6+ for Nb5+ in Ba3W1+ xNb1- xO8.5+ x/2 leads to an increase in the oxygen content, which enhances the low-temperature ionic conductivity. However, at 400 °C, the ionic conductivity of Ba3W1.2Nb0.8O8.6 is still significantly lower than the molybdenum compound Ba3MoNbO8.5. Remarkably, at 600 °C the bulk oxide ionic conductivities of Ba3MoNbO8.5, Ba3WNbO8.5, and Ba3W1.2Nb0.8O8.6 are very similar (σb = 0.0022, 0.0017, and 0.0016 S cm-1, respectively). The variable-temperature neutron diffraction results reported here demonstrate that Ba3W1.2Nb0.8O8.6 undergoes a similar structural rearrangement to Ba3MoNbO8.5 above 300 °C, but the ratio of (W/Nb)O4 tetrahedra to (W/Nb)O6 octahedra rises at a faster rate upon heating between 300 and 600 °C. There is a clear relationship between the ionic conductivity of Ba3M'1+ xM''1- xO8.5+ x/2 (M' = W, Mo; M'' = Nb) phases and the number of tetrahedrally coordinated M' and M ″ cations present within the crystal structure.

Electrical and Structural Characterization of Ba3Mo1-xNb1+xO8.5-x/2: The Relationship between Mixed Coordination, Polyhedral Distortion and the Ionic Conductivity of Ba3MoNbO8.5.

The electrical and structural properties of the series Ba3Mo1-xNb1+xO8.5-x/2 (x = 0.0, 0.1, 0.2, 0.3) have been determined. Ba3Mo1-xNb1+xO8.5-x/2 crystallizes in a hybrid of the 9R hexagonal perovskite and palmierite structures, in which (Mo/Nb)O4 and (Mo/Nb)O6 units coexist within the structure. Nb substitutes preferentially at the octahedral site so that the ratio of (Mo/Nb)O4 tetrahedra to (Mo/Nb)O6 octahedra decreases with increasing x resulting in a reduction in the magnitude of the ionic conductivity from 1.3 × 10-6 S cm-1 for x = 0.0 to 1.1 × 10-7 S cm-1 for x = 0.3 at 300 °C. However, upon heating the conductivities of the solid solution converge, which suggests that the unusual thermal structural rearrangement previously reported for Ba3MoNbO8 preserves the high temperature conductivity. The results demonstrate that the presence of (Mo/Nb)O4 tetrahedra with nonbridging apical oxygen atoms is an important prerequisite for the ionic conduction observed in the Ba3MoNbO8.5 system.

The Crystal Structure of Ba3Nb2O8 Revisited: A Neutron Diffraction and Solid-State NMR Study.

The structure of Ba3Nb2O8 has been investigated using high resolution neutron powder diffraction. Our results show that, while the structure has some features in common with the 9R perovskite and palmierite structures, it is a new and distinct structure. It is shown to follow a (chh)(hhc)(chh) sequence with BaO3-δ packing layers and is a cation- and anion-deficient 9H perovskite polytype. Nb atoms occupy octahedral sites with vacancies between hexagonal close-packed layers. Isolated, corner-sharing and face-sharing Nb-O octahedra all occur within the unit cell. The identification of purely octahedral Nb is supported by solid-state 93Nb wideline NMR measurements. A two-component line shape was detected: a narrow featureless resonance with an isotropic chemical shift of δiso -928 ± 5 ppm consistent with regular Nb octahedra, and a much broader featureless resonance with an approximate isotropic chemical shift in the range δiso ∼ -944 to -937 ± 10 ppm consistent with Nb octahedra influenced by O vacancies. These are both characteristic of 6-fold oxo-coordinated Nb environments. The highly distorted octahedral environments in Ba3Nb2O8 make it a potential candidate for dielectric and photocatalytic applications.

Oxide Ion Conductivity in the Hexagonal Perovskite Derivative Ba3MoNbO8.5.

Oxide ion conductors are important materials with a range of technological applications and are currently used as electrolytes for solid oxide fuel cells and solid oxide electrolyzer cells. Here we report the crystal structure and electrical properties of the hexagonal perovskite derivative Ba3MoNbO8.5. Ba3MoNbO8.5 crystallizes in a hybrid of the 9R hexagonal perovskite and palmierite structures. This is a new and so far unique crystal structure that contains a disordered distribution of (Mo/Nb)O6 octahedra and (Mo/Nb)O4 tetrahedra. Ba3MoNbO8.5 shows a wide stability range and exhibits predominantly oxide ion conduction over a pO2 range from 10-20 to 1 atm with a bulk conductivity of 2.2 × 10-3 S cm-1 at 600 °C. The high level of conductivity in a new structure family suggests that further study of hexagonal perovskite derivatives containing mixed tetrahedral and octahedral geometry could open up new horizons in the design of oxygen conducting electrolytes.

The role of the chemical composition of monetite on the synthesis and properties of α-tricalcium phosphate.

There has been a resurgence of interest in alpha-tricalcium phosphate (α-TCP), with use in cements, polymer composites and in bi- and tri-phasic calcium phosphate bone grafts. The simplest and most established method for preparing α-TCP is the solid state reaction of monetite (CaHPO4) and calcium carbonate at high temperatures, followed by quenching. In this study, the effect of the chemical composition of reagents used in the synthesis of α-TCP on the local structure of the final product is reported and findings previously reported pertaining to the phase composition and stability are also corroborated. Chemical impurities in the monetite reagents were identified and could be correlated to the calcium phosphate products formed; magnesium impurities favoured the formation of ß-TCP, whereas single phase α-TCP was favoured when magnesium levels were low. Monetite synthesised in-house exhibited a high level of chemical purity; when this source was used to produce an α-TCP sample, the α-polymorph could be obtained by both quenching and by cooling to room temperature in the furnace at rates between 1 and 10°C/min, thereby simplifying the synthesis process. It was only when impurities were minimised that the 12 phosphorus environments in the α-TCP structure could be resolved by (31)P nuclear magnetic resonance; samples containing chemical impurity showed differing degrees of line-broadening. Reagent purity should therefore be considered a priority when synthesising/characterising the α-polymorph of TCP.

Colossal magnetoresistance in Mn2+ oxypnictides NdMnAsO(1-x)F(x).

Colossal magnetoresistance is a rare phenomenon in which the electronic resistivity of a material can be decreased by orders of magnitude upon application of a magnetic field. Such an effect could be the basis of the next generation of memory devices. Here we report CMR in the antiferromagnetic oxypnictide NdMnAsO(1-x)F(x) as a result of competition between an antiferromagnetic insulating phase and a paramagnetic semiconductor upon application of a magnetic field. Mn(2+) oxypnictides are relatively unexplored, and tailored synthesis of novel compounds could result in an array of materials for further investigation and optimization.

Giant magnetoresistance in oxypnictides (La,Nd)OMnAs.

A sizeable negative magnetoresistance (MR) has been observed for oxypnictides LnOMnAs (Ln = La,Nd). MR up to -24% is observed at 200 K for LaOMnAs which is unprecedented for divalent Mn(2+). Both materials are weak ferromagnets with transition temperatures above room temperature.

µ-Acetato-bis-(µ-2-{[(3-chloro-2-hydroxy-prop-yl)(2-pyridylmeth-yl)amino]meth-yl}phenolato)dinickel(II) chloride.

The title salt, [Ni(2)(C(16)H(18)ClN(2)O(2))(2)(CH(3)COO)]Cl, features a dinuclear cation in which the Ni atoms are triply bridged by two phenolate O ligands and a bidentate acetate ligand with all of the bridging distances essentially symmetric. Each Ni atom is also coordinated by the amine N, pyridine N and hydr-oxy O atoms of the 2-{[(3-chloro-2-hydroxy-prop-yl)(2-pyridylmeth-yl)amino]meth-yl}phenolate ligand which is, therefore, penta-dentate. The resultant N(3)O(3) donor sets define octa-hedral coordination geometries. The chloride counter-anion is connected to the cation via two O(hydr-oxy)-H⋯Cl hydrogen bonds.

Methyl 1-{4-[(S)-2-(meth-oxy-carbon-yl)pyrrolidin-1-yl]-3,6-dioxocyclo-hexa-1,4-dien-1-yl}pyrrolidine-2-carboxyl-ate.

The complete mol-ecule of the title diproline ester quinone, C(18)H(22)N(2)O(6), is generated by a crystallographic twofold axis, which passes through the centre of the benzene ring. Both -CO(2)Me groups are orientated to the same side of the benzene ring, with the carbonyl groups pointing roughly towards each other. The conformation of the proline residue is an envelope. In the crystal, a three-dimensional network is sustained by C-H⋯O inter-actions involving both the quinone and carbonyl O atoms.

A comparison of cortical and trabecular bone from C57 Black 6 mice using Raman spectroscopy.

Cortical and trabecular bone are both produced and maintained by the same cell types. At the microscopic scale they have a similar lamellar structure but at a macroscopic scale they are very different. Raman microscopy has been used to investigate compositional differences in the two bone types using bone from standard laboratory mice in physiological conditions. Clear differences were observed when complete spectra were compared by principal component analysis (PCA). Analysis of individual bands showed cortical bone to have compositional characteristics of older bone when compared with trabecular material, possibly due to the higher bone turnover traditionally reported in the trabecular compartment.

Bis[1-(isopropyl-ideneamino)guanidinium] bis-(3-nitro-benzoate) monohydrate.

The asymmetric unit of the title salt hydrate, 2C(4)H(11)N(4) (+)·2C(7)H(4)NO(4) (-)·H(2)O, comprises two independent 1-(isopropyl-ideneamino)guanidinium cations, two independent 3-nitro-benzoate anions and a water mol-ecule of crystallization. There are minimal geometric differences between the two planar [maximum deviations 0.061 (2) and 0.088 (2) Å] cations, and between the two almost planar anions [C-C-C-O and C-C-N-O torsion angles of 0.3 (3) and 11.1 (4) °, respectively in the first anion and -173.7 (2) and -0.1 (4), respectively in the second anion]. Extensive O-H⋯O and N-H⋯O hydrogen bonding between all components of the structure leads to the formation of a two-dimensional array with an undulating topology in the bc plane.

1-[2-(Carboxy-meth-oxy)phen-yl]-N-(4-chloro-phen-yl)methanimine oxide.

In the title resonance conformer, C(15)H(12)ClNO(4), the central C-N bond [1.297 (2) Å] has considerable double-bond character and the N-O bond [1.3215 (18) Å] indicates formal negative charge on the oxygen atom. Considerable deviations from co-planarity are evident in the mol-ecule, with both benzene rings twisted out of the central C-C-N-C plane [the dihedral angle formed between the rings = 81.99 (8)°]. Similarly, the carboxylic acid residue occupies a position almost normal to the plane of the benzene ring to which it is connected [C-C-O-C torsion angle = -78.42 (17)°]. The most prominent inter-molecular inter-actions involve the carboxylic acid the N(+)-O(-) residues with the O-H⋯O hydrogen bonds leading to helical supra-molecular chains along the b axis. These chains are connected into layers via C-H⋯O(carbon-yl) inter-actions and the layers are consolidated into the crystal structure by C-H⋯Cl contacts.

Cyclic and acyclic products from the reactions between methyl 3-oxobutanoate and arylhydrazines.

The molecules of methyl 3-(2-nitrophenylhydrazono)butanoate, C(11)H(13)N(3)O(4), (I), and methyl 3-(2,4-dinitrophenylhydrazono)butanoate, C(11)H(12)N(4)O(6), (II), both prepared from methyl 3-oxobutanoate and the corresponding nitrophenylhydrazine, exhibit polarized molecular electronic structures; in each of (I) and (II), the molecules are linked into chains by a single C-H...O hydrogen bond. The molecules of 5-hydroxy-3-methyl-1-phenyl-1H-pyrazole, C(10)H(10)N(2)O, (III), prepared by the reaction of methyl 3-oxobutanoate and phenylhydrazine, are linked into chains by a single O-H...N hydrogen bond. The reaction between methyl 3-oxobutanoate and 3-nitrophenylhydrazine yields 5-hydroxy-3-methyl-1-(3-nitrophenyl)-1H-pyrazole, (IV), which when crystallized from acetone yields 4-isopropylidene-3-methyl-1-(3-nitrophenyl)-1H-pyrazol-5(4H)-one, C(13)H(13)N(3)O(3), (V).

Isomeric N-(iodophenyl)nitrobenzamides form different three-dimensional framework structures.

The isomeric N-(iodophenyl)nitrobenzamides, C(13)H(9)IN(2)O(3), all form different three-dimensional framework structures. Molecules of N-(2-iodophenyl)-3-nitrobenzamide (II) are linked by a combination of N-H...O and C-H...O hydrogen bonds and a two-centre iodo...carbonyl interaction. The supramolecular structure of N-(2-iodophenyl)-4-nitrobenzamide (III) is built from one N-H...O and two C-H...O hydrogen bonds, but short I...O contacts are absent from the structure. In N-(3-iodophenyl)-2-nitrobenzamide (IV), which crystallizes with Z' = 2 in space group P2(1), the structure contains two N-H...O hydrogen bonds, four C-H...O hydrogen bonds, two two-centre iodo...nitro interactions and an aromatic pi...pi stacking interaction. The structure of N-(3-iodophenyl)-3-nitrobenzamide (V) contains one N-H...O hydrogen bond and three C-H...O hydrogen bonds, together with a two-centre iodo...nitro interaction and an aromatic pi...pi stacking interaction, while in N-(3-iodophenyl)-4-nitrobenzamide (VI), the combination of one N-H...O hydrogen bond and two C-H...O hydrogen bonds is augmented not only by a two-centre iodo...nitro interaction and an aromatic pi...pi stacking interaction, but also by a dipolar carbonyl...carbonyl interaction. In the supramolecular structure of N-(4-iodophenyl)-4-nitrobenzamide (IX), which crystallizes with Z' = 2 in space group P\overline 1, there are two N-H...O hydrogen bonds, four C-H...O hydrogen bonds and two three-centre iodo...nitro interactions.

Isomers and polymorphs of (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadienes.

The structures of five of the possible six isomers of (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadiene are reported, including two polymorphs of one of the isomers. (E,E)-1,4-Bis(2-nitrophenyl)-2,3-diaza-1,3-butadiene, C(14)H(10)N(4)O(4) (I), crystallizes in two polymorphic forms (Ia) and (Ib) in which the molecules lie across centres of inversion in space groups P2(1)/n and P2(1)/c, respectively: the molecules in (Ia) and (Ib) are linked into chains by aromatic pi...pi stacking interactions and C-H...pi(arene) hydrogen bonds, respectively. Molecules of (E,E)-1-(2-nitrophenyl)-4-(3-nitrophenyl)-2,3-diaza-1,3-butadiene (II) are linked into sheets by two independent C-H...O hydrogen bonds. The molecules of (E,E)-1,4-bis(3-nitrophenyl)-2,3-diaza-1,3-butadiene (III) lie across inversion centres in the space group P2(1)/n, and a combination of a C-H...O hydrogen bond and a pi...pi stacking interaction links the molecules into sheets. A total of four independent C-H...O hydrogen bonds link the molecules of (E,E)-1-(3-nitrophenyl)-4-(4-nitrophenyl)-2,3-diaza-1,3-butadiene (IV) into sheets. In (E,E)-1,4-bis(4-nitrophenyl)-2,3-diaza-1,3-butadiene (V) the molecules, which lie across centres of inversion in the space group P2(1)/n, are linked by just two independent C-H...O hydrogen bonds into a three-dimensional framework.

4-Iodo-N,N-bis(2-nitrophenylsulfonyl)aniline: a three-dimensional framework structure built from six independent C-H...O hydrogen bonds.

In the title compound [systematic name: 4-iodophenylimino bis(2-nitrobenzenesulfinate)], C(18)H(12)IN(3)O(8)S(2), where the molecules do not exhibit even approximate local symmetry, the molecules are linked into a complex three-dimensional structure by six independent C-H...O hydrogen bonds, which utilize O atoms in nitro and sulfonyl groups as the acceptors.