Vacuum-ultraviolet irradiation of pyridine:acetylene ices relevant to Titan astrochemistry.

Nitrogen-containing polycyclic aromatic hydrocarbons (NPAHs) are important molecules for astrochemistry and prebiotic chemistry, as their occurrence spans from interstellar molecular clouds to planetary systems. Their formation has been previously explored in gas phase experiments, but the role of solid-state chemical reactions in their formation under cryogenic conditions remains elusive. Here, we explore the formation of NPAHs through vacuum ultraviolet (VUV) irradiation of pyridine:acetylene ices in amorphous and co-crystalline phases, with the aim to simulate conditions relevant to the interstellar medium and Titan's atmosphere.

Exploring Phase Transition and Structural Complexity in the Mixed Cation Uranium Oxide CaUNbO.

The structures and high-temperature phase transition of CaUNbO were studied in situ using synchrotron X-ray and neutron powder diffraction. Rietveld refinements provided an accurate description of the crystal structures of both the monoclinic fergusonite-type 2/ structure observed at room temperature and the tetragonal scheelite-type 4/ structure found at high temperatures. Bond valence sum analysis showed Nb to be octahedrally coordinated in the monoclinic fergusonite-type structure, akin to other NbO materials.

Propyne: Determination of Physical Properties and Unit Cell Parameters under Titan-Relevant Conditions.

With its large size, dense atmosphere, methane-based hydrological-like cycle, and diverse surface features, the Saturnian moon Titan is one of the most unique of the outer Solar System satellites. Study of the photochemically produced molecules in Titan's atmosphere is critical in order to understand the mechanics of the atmosphere and, by extension, the interactions between atmosphere, surface, and subsurface water ocean. One example is propyne vapor, a photochemically produced species in Titan's upper atmosphere expected to condense in Titan's stratosphere at lower altitudes.

Intercalated Water Drives Anomalous Thermal Expansion in the Tetragonal Zircon Structured Bismuth Vanadate BiVO Photocatalyst.

The thermal transformation of the tetragonal-zircon (tz-) to tetragonal-scheelite (ts-)BiVO was studied by in situ synchrotron X-ray diffraction, thermogravimetric analysis, and Fourier-transformed infrared spectroscopy. Upon heating, the tetragonal zircon polymorph of BiVO (tz-BiVO) transitioned to the ts-polymorph between 693-773 K. Above 773 K, single phase ts-BiVO was observed before transitioning to the monoclinic fergusonite (mf-) polymorph upon cooling.

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.

Crystals in the community and the classroom.

The growing pressure on school curricula has meant crystals and the science of crystallography have been cut from or made optional for many educational programs. This omission is a serious disservice to the history and understanding of modern sciences, given that crystallography underpins many of the greatest advancements in science over the past century, is a critical component of many modern research papers and patents, and has 29 Nobel Prizes awarded in the field. This contribution describes a simple activity to target classroom and public engagement with crystallography, using marshmallows or equivalent sweets/candy to represent atoms and cocktail sticks to represent bonds, together with examples of how crystals are studied and how they are useful.

Simulation of Cocrystal Formation in Planetary Atmospheres: The CH:CH Cocrystal Produced by Gas Deposition.

The formation of molecular cocrystals in condensed aerosol particles has been recently proposed as an efficient pathway for generation of complex organics in Titan's atmosphere. It follows that cocrystal precipitation may facilitate the transport of biologically important precursors to the surface to be sequestered in an organic karstic and sand environment. Recent laboratory studies on these planetary minerals have predominantly synthesized cocrystals by the controlled freezing of binary mixtures from the liquid phase, allowing for their structural and spectroscopic characterization.

Interface-Driven Multiferroicity in Cubic BaTiO-SrTiO Nanocomposites.

Perovskite multiferroics have drawn significant attention in the development of next-generation multifunctional electronic devices. However, the majority of existing multiferroics exhibit ferroelectric and ferromagnetic orderings only at low temperatures. Although interface engineering in complex oxide thin films has triggered many exotic room-temperature functionalities, the desired coupling of charge, spin, orbital and lattice degrees of freedom often imposes stringent requirements on deposition conditions, layer thickness and crystal orientation, greatly hindering their cost-effective large-scale applications.

Use of a miniature diamond-anvil cell in a joint X-ray and neutron high-pressure study on copper sulfate pentahydrate.

Single-crystal X-ray and neutron diffraction data are usually collected using separate samples. This is a disadvantage when the sample is studied at high pressure because it is very difficult to achieve exactly the same pressure in two separate experiments, especially if the neutron data are collected using Laue methods where precise absolute values of the unit-cell dimensions cannot be measured to check how close the pressures are. In this study, diffraction data have been collected under the same conditions on the same sample of copper(II) sulfate pentahydrate, using a conventional laboratory diffractometer and source for the X-ray measurements and the Koala single-crystal Laue diffractometer at the ANSTO facility for the neutron measurements.

The crystal structure, thermal expansion and far-IR spectrum of propanal (CHCHCHO) determined using powder X-ray diffraction, neutron scattering, periodic DFT and synchrotron techniques.

The crystal structure of propanal has been determined using powder X-ray diffraction (PXRD), where this common laboratory aldehyde is measured to crystallise in spacegroup 21/, = 4 with a unit cell = 8.9833(6) Å, = 4.2237(2) Å, = 9.

Neutron diffraction study of the monoclinic - tetragonal phase transition in NdNbO and NdTaO.

Phase transition and high-temperature properties of NdNbO and NdTaO were studied in situ using powder neutron diffraction methods. Both oxides undergo a reversible phase transition from a monoclinic I2/a phase at low temperatures to a tetragonal I4/a phase at high temperatures. The phase transition has been investigated through analysis of the spontaneous strains and symmetry distortion modes.

Titan in a Test Tube: Organic Co-crystals and Implications for Titan Mineralogy.

In this Account, we highlight recent work in the developing field of mineralogy of Saturn's moon Titan, focusing on binary co-crystals of small organic molecules. Titan has a massive inventory of organic molecules on its surface that are formed via photochemistry in the atmosphere and likely processing on the surface as well. Physical processes both in the atmosphere and on the surface can lead to molecules interacting at cryogenic temperatures.

Re-examining the crystal structure behaviour of nitrogen and methane.

In the light of NASA's mission, the solid-phase behaviour of methane and nitrogen has been re-examined and the thermal expansion coefficients of both materials have been determined over their whole solid temperature range for the first time. Neutron diffraction results indicate that the symmetric 3 space group is the best description for the α-nitrogen structure, rather than the long-accepted 23. Furthermore, it is also observed that β-nitrogen and methane phase I show changes in texture on warming, indicating grain growth.

The Effect of Sterically Active Ligand Substituents on Gas Adsorption within a Family of 3D Zn-Based Coordination Polymers.

An investigation of the adsorption properties of two structurally related, 3D coordination polymers of composition Zn(2-Mehba) and Zn(2,6-Mehba) (2-Mehba = the dianion of 2-methyl-4-hydroxybenzoic acid and 2,6-Mehba = the dianion of 2,6-dimethyl-4-hydroxybenzoic acid) is presented. A common feature of these structures are parallel channels that are able to accommodate appropriately sized guest molecules. The structures differ with respect to the steric congestion within the channels arising from methyl groups appended to the bridging ligands of the network.

Rhenium(i) complexation-dissociation strategy for synthesising fluorine-18 labelled pyridine bidentate radiotracers.

A novel fluorine-18 method employing rhenium(i) mediation is described herein. The method was found to afford moderate to high radiochemical yields of labelled rhenium(i) complexes. Subsequent thermal dissociation of the complexes enabled the radiosynthesis of fluorine-18 labelled pyridine bidentate structures which could not be radiofluorinated hitherto.

Neutron diffraction of deuterated tripalmitin and the influence of shear on its crystallisation.

This neutron diffraction study of deuterated tripalmitin has provided further insight into a forensic observation of the crystallisation of lipids under high-shear conditions. To achieve this, an experimental set up was designed to enable simultaneous rheological data from a Couette cell to be recorded with neutron powder diffraction, enabling the influence of shear on the polymorph transformation on cooling to be monitored in real time. Tripalmitin was observed to directly transform from a liquid phase to a β polymorph under the influence of shear.

Squeezing electrons out of 6s lone-pairs in perovskite-type oxides.

Having identified a set of conditions that predispose a solid-state ionic compound to a pressure-induced valence transition, we investigated a series of Bi(iii) perovskite oxides. We found such a transition below 10 GPa in every case, including one that we synthesised for the first time (double perovskite-type Ba2BiOsO6).

Crossover between liquidlike and gaslike behavior in CH_{4} at 400 K.

We report experimental evidence for a crossover between a liquidlike state and a gaslike state in fluid methane (CH_{4}). This crossover is observed in all of our experiments, up to a temperature of 397 K, 2.1 times the critical temperature of methane.

Structural and Magnetic Properties of the Osmium Double Perovskites BaSrYOsO.

The crystal and magnetic structures of double perovskites of the type BaSrYOsO were studied by synchrotron X-ray and neutron powder diffraction methods, bulk magnetic susceptibility measurements, and X-ray absorption spectroscopy. The structures were refined using combined neutron and synchrotron data sets based on an ordered array of corner-sharing YO and OsO octahedra, with the Ba/Sr cations being completely disordered. The structure evolves from cubic to monoclinic Fm3̅m (x ≈ 0.

Deformation-resembling microstructure created by fluid-mediated dissolution-precipitation reactions.

Deformation microstructures are widely used for reconstructing tectono-metamorphic events recorded in rocks. In crustal settings deformation is often accompanied and/or succeeded by fluid infiltration and dissolution-precipitation reactions. However, the microstructural consequences of dissolution-precipitation in minerals have not been investigated experimentally.

A co-crystal between benzene and ethane: a potential evaporite material for Saturn's moon Titan.

Using synchrotron X-ray powder diffraction, the structure of a co-crystal between benzene and ethane formed in situ at cryogenic conditions has been determined, and validated using dispersion-corrected density functional theory calculations. The structure comprises a lattice of benzene molecules hosting ethane molecules within channels. Similarity between the intermolecular interactions found in the co-crystal and in pure benzene indicate that the C-H⋯π network of benzene is maintained in the co-crystal, however, this expands to accommodate the guest ethane molecules.

An indirect generation of 1D M(II)-2,5-dihydroxybenzoquinone coordination polymers, their structural rearrangements and generation of materials with a high affinity for H2, CO2 and CH4.

A series of solid-state structural transformations are found to accompany desolvation of relatively simple coordination polymers to yield materials that exhibit unexpected gas sorbing properties. Reaction of 1,2,4,5-tetrahydroxybenzene with M(II) salts (M = Mg, or Zn) in an alcohol/water solution in the presence of air affords cis-M(II)(C6H2O4(-II))(H2O)2·2H2O·xROH, (M = Mg, or Zn), crankshaft-like chains in which the absolute configurations of the chiral metal centres follow the pattern Δ Δ Λ Λ Δ Δ Λ Λ, and are hydrogen bonded together to generate spacious channels. When crystals of the crankshaft chain are air dried the crystals undergo a single crystal-to-powder rearrangement to form linear trans-M(II)(C6H2O4(-II))(H2O)2 chains.

A New Structural Family of Gas-Sorbing Coordination Polymers Derived from Phenolic Carboxylic Acids.

The structure of Li(inox)⋅2/3 DMF (inox(-) =the N-oxide of the isonicotinate anion) consists of a 3D framework with solvent-filled, square cross-section channels of approximate dimensions 5.5×5.5 Å.

The crystal structure of methane B at 8 GPa--an α-Mn arrangement of molecules.

From a combination of powder and single-crystal synchrotron x-ray diffraction data we have determined the carbon substructure of phase B of methane at a pressure of ∼8 GPa. We find this substructure to be cubic with space group I4¯3m and 58 molecules in the unit cell. The unit cell has a lattice parameter a = 11.

Isomeric ionic lithium isonicotinate three-dimensional networks and single-crystal-to-single-crystal rearrangements generating microporous materials.

Reaction between LiOH and isonicotinic acid (inicH) in the appropriate solvent or mixture of solvents affords a family of variously solvated forms of a simple ionic lithium salt, viz., Li(+)inic(-)·S (where S = 0.5 morpholine, 0.