Synthesis, Structure, and Properties of 2O-BaPtO, a Phase Derived from Hexagonal Perovskite.

We have made the compound 2O-BaPtO by high-pressure, high-temperature synthesis, determined its structure, and tested its catalytic activity. Compounds of the same stoichiometry have been reported and tentatively identified as hexagonal perovskites, and although no structural model was ever established, 2O-BaPtO is clearly different and, to the best of our knowledge, unique. It features continuous chains of face-sharing PtO octahedra, like the well-known 2H hexagonal perovskite type, but with a staggered offset between the chains that breaks hexagonal symmetry and disrupts the close-packed array of = Ba and = O that is a defining characteristic of perovskites.

Understanding the Correlation between Oxide Ion Mobility and Site Distributions in BaNbWO.

A correlation between oxygen site distributions and ionic conductivity has been established in the recently discovered family of oxide-ion conductors BaO (M = Nb, V, Mo, W). We rationalize this observation on the basis of structural insights gained from the first single-crystal neutron diffraction data collected for a member of this family, BaNbWO, and theoretical considerations of bonding and O site energies.

Order, Disorder, and Dynamics in Brownmillerite SrFeO.

The room-temperature structure of brownmillerite-type SrFeO remains controversial, despite numerous published crystallographic studies utilizing X-ray, neutron, and electron diffraction data collected on single-crystalline and powder samples. The main disagreements concern the ordering of twisted FeO tetrahedral chains within and between the layers stacked along the axis, and the impact of this ordering on oxide-ionic conductivity. Here, we present new data along with a reinterpretation of previously published diffraction images, including the reassignment of satellite reflections, which harmonize the results of past studies in a unified description of tetrahedral chain ordering in SrFeO at length scales relevant to X-ray and neutron diffraction.

Square Grid Metal-Chloranilate Networks as Robust Host Systems for Guest Sorption.

Reaction of the chloranilate dianion with Y(NO ) in the presence of Et N in the appropriate proportions results in the formation of (Et N)[Y(can) ], which consists of anionic square-grid coordination polymer sheets with interleaved layers of counter-cations. These counter-cations, which serve as squat pillars between [Y(can) ] sheets, lead to alignment of the square grid sheets and the subsequent generation of square channels running perpendicular to the sheets. The crystals are found to be porous and retain crystallinity following cycles of adsorption and desorption.

Continuous negative-to-positive tuning of thermal expansion achieved by controlled gas sorption in porous coordination frameworks.

Control of the thermomechanical properties of functional materials is of great fundamental and technological significance, with the achievement of zero or negative thermal expansion behavior being a key goal for various applications. A dynamic, reversible mode of control is demonstrated for the first time in two Prussian blue derivative frameworks whose coefficients of thermal expansion are tuned continuously from negative to positive values by varying the concentration of adsorbed CO. A simple empirical model that captures site-specific guest contributions to the framework expansion is derived, and displays excellent agreement with the observed lattice behaviour.

Anisotropic Thermal and Guest-Induced Responses of an Ultramicroporous Framework with Rigid Linkers.

The interdependent effects of temperature and guest uptake on the structure of the ultramicroporous metal-organic framework [Cu (cdm) ] (cdm=C(CN) (CONH ) ) were explored in detail by using in situ neutron scattering and density functional theory calculations. The tetragonal lattice displays an anisotropic thermal response related to a hinged "lattice-fence" mechanism, unusual for this topology, which is facilitated by pivoting of the rigid cdm anion about the Cu nodes. Calculated pore-size metrics clearly illustrate the potential for temperature-mediated adsorption in ultramicroporous frameworks due to thermal fluctuations of the pore diameter near the value of the target guest kinetic diameter, though in [Cu (cdm) ] this is counteracted by a competing contraction of the pore with increasing temperature as a result of the anisotropic lattice response.

Real-time powder diffraction studies of energy materials under non-equilibrium conditions.

Energy materials form the central part of energy devices. An essential part of their function is the ability to reversibly host charge or energy carriers, and analysis of their phase composition and structure in real time under non-equilibrium conditions is mandatory for a full understanding of their atomic-scale functional mechanism. Real-time powder diffraction is increasingly being applied for this purpose, forming a critical step in the strategic chemical engineering of materials with improved behaviour.

Type II Bi1 - xWxO1.5 + 1.5x: a (3 + 3)-dimensional commensurate modulation that stabilizes the fast-ion conducting delta phase of bismuth oxide.

The Type II phase in the Bi1 - xWxO1.5 + 1.5x system is shown to have a (3 + 3)-dimensional modulated δ-Bi2O3-related structure, in which the modulation vector ℇ `locks in' to a commensurate value of 1/3.

Pressure-induced intersite Bi-M (M=Ru, Ir) valence transitions in hexagonal perovskites.

Pressure-induced charge transfer from Bi to Ir/Ru is observed in the hexagonal perovskites Ba(3+n)BiM(2+n)O(9+3n) (n=0,1; M=Ir,Ru). These compounds show first-order, circa 1% volume contractions at room temperature above 5 GPa, which are due to the large reduction in the effective ionic radius of Bi when the 6s shell is emptied on oxidation, compared to the relatively negligible effect of reduction on the radii of Ir or Ru. They are the first such transitions involving 4d and 5d compounds, and they double the total number of cases known.

Coexistence of spin glass and antiferromagnetic orders in Ba3Fe2.15W0.85O8.72.

Ba(3)Fe(2.15)W(0.85)O(8.