Preparation and Crystal Structure of PbRe2O6. An Example of the Re2O10 Unit with No Metal-Metal Bonding

Single crystals of PbRe₂O₆ were obtained from a stoichiometric mixture of PbO and ReO₃ at 500°C. The structure was determined by Patterson methods from X-ray four-circle diffractometer data using 2 270 (392 unique) reflections; R_W(F) = 0.036. PbRe₂O₆ crystallizes in the trigonal space group R3m with a = 10.359(6) Å, c = 11.092(6) Å and Z = 9. The compound is isotypic with the trigonal modification of PbNb₂O₆ and contains an Re₂O₁₀ unit. Unlike other compounds containing this species, there is no metal-metal bonding.     

New ideas in neutrino detection

What is new in the field of neutrino detection? In addition to new projects probing both the low and high ends of the neutrino energy scale, an inexpensive, effective technique is being developed to allow tagging of antineutrinos in water Cherenkov (WC) detectors via the addition to water of a solute with a large neutron cross-section and energetic γ daughters. Gadolinium is an excellent candidate since in recent years it has become very inexpensive, now less than $8 per kilogram in the form of commercially available gadolinium trichloride. This non-toxic, non-reactive substance is highly soluble in water. Neutron capture on gadolinium yields an 8.0 MeV gamma cascade easily seen in detectors like Super-Kamiokande. The uses of GdCl₃ as a possible upgrade for the Super-Kamiokande detector — with a view toward improving its performance as an antineutrino detector for supernova neutrinos and reactor neutrinos — are discussed, as are the ongoing R&;D efforts which aim to make this dream a reality within the next two years.     

A comparative study of the electron- and hole-doped compositions of single crystalline Nd1−xCaxMnO3 ( and 0.4) by Brillouin scattering

In order to understand the differences between the nature of the electron- and the hole-doped compositions of rare earth manganates, properties of single crystals of Nd_1−xCa_xMnO₃ with x=0.6 and 0.4 have been investigated. In the electrical resistivity measurements, the electron-doped (x=0.6) composition shows no effect of magnetic field unlike the hole-doped (x=0.4) composition, but both exhibit similar current-induced changes. Brillouin scattering studies show that the x=0.6 and 0.4 compositions show softening of the modes on cooling the samples towards charge-ordering transitions. The strength of coupling between the e_g orbitals and the elastic strain is considerably larger in the hole-doped composition containing a larger population of Mn³⁺ ions.     

Open-Framework Inorganic Materials

Aluminosilicate zeolites such as UTD-1 (structure shown) belong to a family of nanoporous inorganic materials that find utility in catalysis, separation, and ion exchange. During the last decade, the rate of discovery of new open-framework materials based, for example, on phosphates, sulfides, halides, nitrides, and coordination compounds has increased dramatically. The synthesis, structures, and properties of this remarkable class of materials are reviewed.     

Open-Framework Cobalt (II) Phosphates with Sodalite-Related Architectures

Three new framework cobalt (II) phosphates have been synthesized hydrothermally in the presence of piperazine as a structure-directing agent. Crystal data: compound I, [C₄N₂H₁₂][Co(HPO₄)₂], monoclinic space group=P2₁/n 001(no. 14), a=8.5521(10) Å, b=13.5791(15) Å, c=10.0405(11) Å, β=96.855(2)°, V=1157.7(2) ų, Z=4, M=339.04, D_c= 1.945 g m−3, MoKα, λ=0.71073 Å, R₁(F₀)=0.053; compound II, [C₄N₂H₁₁][Co₂(PO₄)(H₂PO₄)₂], monoclinic space group=C2/c (no. 15), a=13.444(5) Å, b=12.874(5) Å, c=8.224(2) Å, β=94.64(2)°, V=1418.8 (2)A 3, Z=8, M=494.96, D_c=2.317 g cm−3, MoKα, λ=0.71073 Å ,R₁(F₀)=0.047; compound III, [C₄N₂H₁₂]₂[Co₄(HPO₄)₆], monoclinic space group=P2₁/c (no. 14) a=12.8780(13) Å, b=26.671(3) Å, c=8.2592(8) Å, β=96.931(2)°, V=2816.0(5) Å3, Z=4, M=987.90, D_c=2.330gcm-3, MoKα, λ=0.71073 Å, R₁(F₀)=0.048. The structure of I consists of one-dimensional chains built up of corner-shared four rings (Co₂P₂) which are key structural units that form the sodalite cage. Compounds II and III have interrupted sodalite-type structures resulting from the removal of Co²⁺ atoms from sites related by two-fold axes passing through the four rings of the normal sodalite cage structure. The modes of the interruptions in II and III differ in relation to the structure of a regular sodalite cage.