Pd Nanostructures Obtained inside Mesoporous Materials
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normally binds with four other atoms or groups tetrahedrally to produce threedimensional structures that have low energy requirements, making them stable, chemists used computational methods to predict that four groups around carbon molecules sometimes can lie in a plane. Several examples created in the laboratory confirmed this theory. Von Ragué Schleyer and his research team in the Center for Computational Quantum Chemistry used computational techniques to investigate the possibility of hexacoordinate molecules with a carbon in the center of six-atom rings. As reported in the December 7 issue of Science, the researchers designed the boron and carbon compounds by fitting the atoms together in optimal ways, ensuring that all bond lengths were in the right ranges. They then checked their predicted planar hexacoordinate structures to verify their stability.
Open-Framework Material Consists of Cerium Oxyfluoride with CeO6F2 Dodecahedron A research team from the Institute of Inorganic Synthesis at Yamanashi University, Japan, has synthesized an open framework material based on actinide oxyfluoride. As reported in the December 2000 issue of Chemistry of Materials, the researchers obtained cerium oxyfluoride by hydrothermal methods. The result is a compound with six dodecahedra of CeO6F2 linked in a basic structure forming an octahedral cage of Ce 6O 24F 12 interconnected by an O bridge, resulting in a channel structure with eight pore openings. The name given to the new cerium oxyfluoride is YU-1 (Yamanashi University) with the formula H25.5(NH4)10.5Ce9O27F18. As a precursor, a mixture was used of 1.0 Ce(SO 4) 2/0.5 H3PO4/1.5 H2N(CH2)2 NH2/4.0 NH4F/150 H2O, which was heat treated at 160–180°C
Figure: Framework of the cerium oxyfluoride YU-1 showing the hexagonal arrangement of the octahedral cages and locations of NH4+ cations. 88
for several days. The crystalline product was washed and filtered with ethanol and deionized water and further dried. Analysis on one of the crystals obtained shows that YU-1 belongs to the space group R3,with the pore sizes and cages dictated by the distances between the centers of the corresponding oxygen and fluoride atoms. The octahedral cages formed by the six corner-sharing, cerium-centered CeO6F2 dodecahedra have a body diagonal of 5.8 Å and give rise to a framework structure with one three-dimensional channel systems. The channel systems connect opposite faces of the supercage and have elliptical eight-ring windows with O - - - O distance between 6.3 Å and 9.7 Å and F - - - F distance between 3.7 Å and 4.4 Å. IULIA MUNTELE
Prism Coupling with Glass Spherical Microresonators Shows Optical Bistability Optical whispering-gallery modes (WGMs) observed in microspheres are optical resonance modes that find useful applications as microspherical lasers. WGMs are widely applied in compact functional photonic devices. Some researchers are paying special attention to the fabrication method of these microspheres since it should produce a sphere with an optically smooth surface. A group of rese
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