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

We performed the polarized neutron diffraction measurements in phase II of CeB 6 to observe the magnetic form factors. By the Maximum Entropy Method (MEM), we obtained the unexpected spin density distribution in CeB 6 . We clearly observed the existence not only at Ce site but also at between B 6 octahedral and at the center of triangle bonding in the B 6 octahedral. This is the first evidence that the magnetic moments are located between the Borons.

Where is the Magnetic Moment in CeB6

Cover Picture: Direct Observation of Hydrogen Molecules Adsorbed onto a Microporous Coordination Polymer (Angew. Chem. Int. Ed. 6/2005)

Endohedral metallofullerenes are novel forms of fullerene-related materials, which encage metal atom inside a carbon cage. The recent X-ray structural studies of metallofullerenes, Sc@C82 and Sc2@C84, by the synchrotron powder diffraction experiment are presented to illustrate the usefulness of the MEM/Rietveld analysis, which is a self-consistent iterative way in combination with the MEM (Maximum Entropy Method) and Rietveld analyses. The obtained MEM charge densities clearly reveal the distinct features of encapsulated metals inside the fullerene cages as well as endohedral cage structures for Sc@C82 and Sc2@C84.

X-ray Structure Determination of Endohedral Metallofullerenes

Element-selective visualization for materials science using synchrotron X-ray two-wavelength anomalous powder diffraction data

Magnetic structure in a layered perovskite manganite, La2-2xSr1+2xMn2O7 (x = 0.307) has been investigated by neutron diffraction measurements. We found that the ground state (at 4 K) has a ferromagnetic structure with magnetic moment of Mn ions being aligned in a direction inclined by 10 degree from the c-axis. The magnetic structure changes to a canted antiferromagnetic one (CAFM-I) at about 20 K and then to another canted antiferromagnetic one (CAFM-II) at about 80 K. Here the magnetic moment lies in the ab-plane in CAFM-II but not in CAFM-I. The magnetic structure then changes to an antiferromagnetic one with magnetic moment lies in the ab-plane at about 90 K, and then to a paramagnetic one at about 100 K.

Masaki Takata

Papers

Where is the Magnetic Moment in CeB6

Cover Picture: Direct Observation of Hydrogen Molecules Adsorbed onto a Microporous Coordination Polymer (Angew. Chem. Int. Ed. 6/2005)

X-ray Structure Determination of Endohedral Metallofullerenes

Element-selective visualization for materials science using synchrotron X-ray two-wavelength anomalous powder diffraction data

Neutron Diffraction Study on Magnetic Structure in Layered Manganite La2-2xSr1+2xMn2O7 (x=0.307)