Long-wavelength macromolecular crystallography（MX）has been proposed for a long time as a tool for phasing novel macromolecular crystal structures without additional heavy atom labelling. Making use of anomalous diffraction from atoms natively present in the crystal, such as sulphur and phosphorus, has become increasingly popular over the past years. Nevertheless, the full potential of this technique, has not been fully exploited due to lack of dedicated experimental setups able to easily access wavelengths longer than 2 Å. Since the wavelengths for the absorption edges of sulphur and phosphorus are significantly longer, standard beamline setups are not suitable to provide high-quality, high-resolution data, as the experiments are limited by the increasing absorption effects and the diffraction angles for longer wavelengths. Currently only two synchrotron beamlines offer access to optimised sample environments using wavelengths longer than 2.7 Å：BL1A at Photon Factory, Japan and I23 at Diamond Light Source, UK. Here, we describe the challenges and solutions implemented at the in-vacuum long-wavelength MX beamline I23 and present first results.
Inorganic compounds such as oxides and nitrides are widely used in various industries including electronic devices, batteries, display and so on. However, despite the large number of constituent elements in these materials, the diversity of atomic coordination is severely limited, which gives constraints in materials design for next generation. In contrast, compounds with multiple anions beyond the single-anion, such as oxyhalides and oxyhydrides, provide a new materials platform which brings new degree of freedom for designing materials. Here, we overview the features, advantages and recent trends of mixed-anion compounds with our recent results of topochemical anion exchange reactions to form various mixed-anion oxides.
The compounds containing multiple anions, so-called mixed anion compounds, has recently begun to be considered as a new frontier of the solid-state chemistry owing to the discovery of several functionalities in these compounds. However, because of the several specific restrictions of the system, synthesis of the mixed anion compounds is generally difficult and needs different approach compared to usual inorganic compounds such as oxides or fluorides. In this report the features of the mixed anion compounds and the effects for their synthesis, as well as recent our study of development of layered mixed anion compounds are summarized.
Recently mixed-anion compounds such as metal oxynitrides have attracted considerable attention in physics, chemistry and materials science. In the present brief review, we describe the structural analyses of the mixed-anion compounds. X-ray and neutron diffractometry is able to refine the crystallographic parameters of the crystalline mixed-anion compounds. Electron-density from X-ray data and neutron-scattering-length-densities from neutron data can give the information on the chemical bonding and structural disordering. Scanning transmission electron microscopy and electron energy-loss spectroscopy allow us to characterize local crystal structures with high spatial resolution. Combination of the information about local structures by X-ray absorption near edge structure and magic angle spinning-nuclear magnetic resonance with those available by the diffraction techniques is effective to tackle the problems peculiar to the mixed anion systems: discrimination of N3－, O2－, and F－, and H－ and OH－.
Mixed anion compounds such as oxynitrides and oxychalcogenides are potential photocatalysts for visible-light water splitting, because p orbitals of less electronegative anion（e.g., N3－, S2－）can form a valence band that has more negative potential than oxygen 2p orbitals. This article describes our recent progress in the development of new mixed anion-type photocatalysts for visible-light-driven water splitting.