VESTA is a three-dimensional visualization system for crystallographic studies and electronic state calculations. It has been upgraded to the latest version, VESTA 3, implementing new features including drawing the external mor­phology of crystals; superimposing multiple structural models, volumetric data and crystal faces; calculation of electron and nuclear densities from structure parameters; calculation of Patterson functions from structure parameters or volumetric data; integration of electron and nuclear densities by Voronoi tessellation; visualization of isosurfaces with multiple levels; determination of the best plane for selected atoms; an extended bond-search algorithm to enable more sophisticated searches in complex molecules and cage-like structures; undo and redo in graphical user interface operations; and significant performance improvements in rendering isosurfaces and calculating slices.

VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data

Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

The Chemistry and Applications of Metal-Organic Frameworks

J. Appl. Cryst.の発刊に際して

Adsorptive separation is very important in industry. Generally, the process uses porous solid materials such as zeolites, activated carbons, or silica gels as adsorbents. With an ever increasing need for a more efficient, energy-saving, and environmentally benign procedure for gas separation, adsorbents with tailored structures and tunable surface properties must be found. Metal–organic frameworks (MOFs), constructed by metal-containing nodes connected by organic bridges, are such a new type of porous materials. They are promising candidates as adsorbents for gas separations due to their large surface areas, adjustable pore sizes and controllable properties, as well as acceptable thermal stability. This critical review starts with a brief introduction to gas separation and purification based on selective adsorption, followed by a review of gas selective adsorption in rigid and flexible MOFs. Based on possible mechanisms, selective adsorptions observed in MOFs are classified, and primary relationships between adsorption properties and framework features are analyzed. As a specific example of tailor-made MOFs, mesh-adjustable molecular sieves are emphasized and the underlying working mechanism elucidated. In addition to the experimental aspect, theoretical investigations from adsorption equilibrium to diffusion dynamics via molecular simulations are also briefly reviewed. Furthermore, gas separations in MOFs, including the molecular sieving effect, kinetic separation, the quantum sieving effect for H2/D2 separation, and MOF-based membranes are also summarized (227 references).

Selective gas adsorption and separation in metal–organic frameworks

Metal–Organic Frameworks for Separations

The charge density distribution map of CaSi2 was obtained by the Maximum Entropy Method(MEM) using synchrotron powder diffraction data. The MEM charge density map reveals that there are two types of Si layers in a unit cell. In both layers, Si atoms form rather strong covalent bond. However, they are not identical. Electron density at bond mid point are slightly different at each layer, i.e. 0.62[e/A3] for one layer, and 0.52[e/A3] for the other. These values shows covalent bond of the former layer is considerably stronger than that of the latter layer. As for the bond lengths, the Si-Si bond length of the former layer is 2.32 A and that of the latter is 2.40 A, respectively. The present direct observation of bond electrons gives one of the examples that the longer the bond length, the weaker the covalent bond. It is not recognized that there exists covalency between Ca-Ca atoms. Since the MEM charge density shows very slight overlap of electron clouds between Ca-Si, the nature of chemical bond of Ca in CaSi2 is almost ionic.

Charge Densities and Chemical Bonding of CaSi2

/pdf/period-spacings-in-red-giants-corrigendum-iii-coupling-3mxolld0k0.pdf

Period spacings in red giants (Corrigendum) - III. Coupling factors of mixed modes

Quantum confinement of carriers and excitons due to the interface charges of copper halide nanocrystals in glass

A new technique to measure the polarization dependence of scattering intensity without using an analyzer crystal has been developed and applied to a magnetic satellite reflection of rare-earth metal dysprosium. We have successfully observed the scattering plane inclination angle ϑ dependence of satellite peak intensity. The magnetic and charge scattering have definitely different ϑ dependence of scattering intensity, which enables us to distinguish the scattering origins.

New technique to measure the polarization dependence of non-resonant X-ray magnetic scattering

https://iopscience.iop.org/article/10.1016/j.stam.2005.11.002/pdf

Masaki Takata

Papers

Charge Densities and Chemical Bonding of CaSi2

Period spacings in red giants (Corrigendum) - III. Coupling factors of mixed modes

Quantum confinement of carriers and excitons due to the interface charges of copper halide nanocrystals in glass

New technique to measure the polarization dependence of non-resonant X-ray magnetic scattering

Crystal symmetry and superlattice reflections in spin-Peierls system TiOBr