Peculiarities in the Raman spectra of ZrB12 and LuB12 single crystals

We have measured Raman spectra of high-quality Zr^natB₁₂, Lu^natB₁₂ and Lu¹¹B₁₂ single crystals with high resolution, and the observed strong peaks are attributed to specific vibration modes. Besides, there are a number of additional Raman peaks in spectral ranges, where only Raman-inactive vibrations of the atomic arrangement are expected. Accordingly, it is assumed, that the investigated crystals contain intrinsic structural imperfections or distortions in sufficient concentration and efficiency to initiate the observed breaking of phonon selection rules. We suppose boron vacancies, boron isotope effects and displacements of the metal atoms to be reasons for such imperfections.     

A concise enantioselective synthesis of the fungal metabolite (+)-decarestrictine L

A stereoselective 10-step synthesis of the fungal metabolite (+)-decarestrictine L from commercially available ethyl (R)-3-hydroxybutyrate is described in which tandem oxonium ylide formation and rearrangement is used to construct the tetrahydropyranyl core of the natural product.     

Pd/Al2O3催化剂的高温热烧结研究

以汽车尾气净化催化剂为背景，用溶胶－凝胶法和浸渍法制备了低负载量贵金属单钯燃烧催化剂。通过ＸＲＤ宽化法检测了在１２７３Ｋ的模拟反应气流中烧结２４ｈ后催化剂上Ｐｄ晶粒大小的变化。     

Evaluation of electroless gold deposited on porous silica for ligand attachment for metal ion-exchange

A novel ion-exchange system was developed by tethering a small, monofunctional metal ligand, 3-mercaptopropionic acid (MPA), through thiol linkages onto a glass substrate overlaid with gold, using electroless deposition of Au onto 100 mesh controlled pore glass (CPG) particles. Two different CPG glass pore sizes of 22.6 and 104.9 nm were used in an attempt to optimize Au deposition and ligand coverage. It was found that the Au was present on both of the substrates as a nonuniform deposit, possibly existing as small multilayer islands, throughout the CPG particles. The deposit also did not fill the intricate CPG pore network.Au-CPG is a reasonable substrate for the support of small metal binding ligands such as the monofunctional MPA. Typical metal binding capacities were in the range of 7-24 μmol metal/g column, with the smaller pore system binding approximately twice as much metal as the larger pore system due to increased surface area and fractional ligand coverage. The immobilized binding systems were also found to remain chemically and structurally stable in pH environments ranging from pH∼9 to <1 (viz. 1 M HNO₃).     

Mercury,a Structural Building Block and Source of Localized Reactivity in Extended Metal–Metal Bonded Systems

Transition metal–mercury complexes were among the first compounds of study for the concept of direct metal–metal bonding which was established more than three decades ago. Since then, a large number of such systems have been synthesized and studied. The fact that mercury is readily attached to a large variety of main group or transition metals has stimulated its use as a general building block in the systematic synthesis of mixed-metal clusters. The past decade has witnessed a rapid expansion of bimetallic cluster chemistry in which species containing mercury have played a prominent role, and which has led to the discovery of many unprecedented cluster structures and reactions. In particular, the ability of mercury to form multicenter metal–metal bonds with polynuclear cluster fragments has substantially extended its coordination chemistry which was thus far dominated by simple linear structural arrangements. Although certain structural motifs are found to be common to many of the transition metal–mercury clusters investigated to date and thus enable a relatively systematic synthetic approach, the multitude of surprising discoveries has kept the interest in the chemistry of the element itself alive. The recent discovery of the redox and photochemical reactivity of some of these systems has opened up an exciting and promising area of cluster research. Its significance for the synthetic methodology lies in the fact that the increasing redox activity of molecular carbonyl clusters on going to higher nuclearities appears to set a limit on the size of metal frameworks attainable by the standard preparative methods. On the other hand, their potential use as photochromes or redox mediaters in coupled electron-transfer reactions provides an additional stimulus for future studies in this field.     

Studies of metal exchange reactions: the synthesis and structures of heteronuclear metal clusters containing the indenyl ligand (μ3-CR)Co2M(CO)8(η- Ind)(R=H,CH3,C6H5,COOC2H5; M=Mo,W)

The novel tetrahedral clusters (μ₃-CR)Co₂M(CO)₈(η⁵-Ind) (M=Mo,W; R=H, CH₃, C₆H₅, COOC₂H₅) 5-12 containing the indenyl ligand were isolated from reactions of tricobalt clusters (μ₃-CR)Co₃(CO)₉ (R=H, CH₃, C₆H₅, COOC₂H₅) and K(η⁵-Ind)M(CO)₃ (M=Mo,W) under mild conditions. The cluster complex (μ₃-CC₆H₅)CoMo₂(CO)₇(η⁵-Ind)(η⁵-Cp (Cp*=C₅H₄C(O)CH₃) 16 was obtained via the stepwise metal exchange reaction of complex (μ₃-CC₆H₅)Co₂Mo(CO)₈(η⁵-Ind) 9 with Na(η⁵-CpMo(CO)₃, but the reaction of (μ₃-CC₆H₅)Co₂Mo(CO)₈(η⁵-Cp*) 15 with K(η⁵-Ind)Mo(CO)₃ yielded only 9. The crystal structures of compounds 7, 9 and 13 were established by single crystal X-ray diffraction methods and show structural evidence for “slippage” of the indenyl ring.     

Co-melting of solid sucrose and multivalent cation soaps for solvent-free synthesis of sucrose esters

Sucrose fatty acid esters, useful as mild surfactants, have been synthesised in good yields in a solvent-free medium. High contents of monoesters and low saponification rate have been observed. The co-melting of sucrose and a multivalent cation soap such as magnesium or zinc soaps, under basic conditions, allowed the formation of a homogeneous reaction mixture, where solid sucrose was fully dissolved. The kinetic monitoring profiles are similar to reactions in homogeneous solutions, with fast initial formation of monoesters. As a consequence, conversion of sucrose in sucrose esters occurred in good yields. The specificity of multivalent cation soaps compared to monovalent cation soaps, for example, potassium stearate, was pointed out.     

Catalytic Effects of Metal-loaded Membrane-like Alumina Tubes on Ammonia Synthesis in Atmospheric Pressure Plasma by Dielectric Barrier Discharge

Plasma synthesis of ammonia was studied at atmospheric pressure using a dielectric-barrier-discharge-plasma reactor equipped with a metal-loaded membrane-like alumina tube as a catalyst between the electrodes. Introducing the pure alumina into N₂–H₂ plasma resulted in an increase in the ammonia yield and the further improvement was achieved by loading the alumina with Ru, Pt, Ni, and Fe. These results clearly demonstrate the catalytic effects of the alumina and the metals in the plasma reaction. Temperature-programmed desorption and isotope exchange reaction of nitrogen revealed that plasma-excited N₂ molecules were subjected to dissociative adsorptions mainly on the alumina to form atomic N(a) (The suffix “(a)” denotes adsorbed species) species, which were converted into ammonia by H₂ plasma. A role of the metals is considered to be acceleration of ammonia formation by the reaction of the alumina-adsorbed N(a) atoms with plasma-activated hydrogen species.     

Effects of processing on five selected metals in the durum wheat food chain

The concentration levels of five metals, namely Cd, Cr, Fe, Ni and Pb, were investigated along the durum wheat processing chain, from grain to the final product. Cadmium and Pb are well-known toxic elements and their levels in wheat grain are regulated by the European legislation. Chromium, Fe and Ni were included in the study as markers of metal release from equipment during processing. Durum wheat grain, semolina and pasta were sampled at an industrial plant for milling and pasta making. Samples were taken at different stages along processing in order to elucidate the influence of each stage on the element content. Samples of the water used for grain tempering and dough preparation were also collected. The whole analytical procedure, from sampling to final analytical determinations, was carried out according to a pre-established quality assurance protocol. Analyses were performed by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES).Milling was the key process influencing the concentrations of the studied elements and reduced the metal levels according to a definite element-specific pattern. Purity of the water used as ingredient, element deposition from plant air and metal release from equipment were identified as critical issues in contamination control during processing. In the conditions of this study, it was found that a simple relationship can be established between the original concentrations in durum wheat grain and those in pasta for Cd and Fe, while for Pb, Cr and Ni, a greater uncertainty in the estimation of the levels in the final product is expected.     

Hydrogen-induced atomic rearrangement in MgPd3

The hydrogenation behavior of MgPd₃ has been studied by in situ X-ray powder diffraction and by neutron powder diffraction. At room temperature and p ≈500 kPa hydrogen pressure its structure is capable of incorporating up to one hydrogen atom per formula unit (α-MgPd₃H_≈1), thereby retaining a tetragonal ZrAl₃-type metal atom arrangement. Upon heating to 750 K in a hydrogen atmosphere of 610 kPa it transforms into a cubic modification with AuCu₃-type metal atom arrangement (β-MgPd₃H_≈0.7). Neutron diffraction on the deuteride reveals an anion deficient anti-perovskite-type structure (β-MgPd₃D_0.67, a=398.200(7) pm) in which octahedral sites surrounded exclusively by palladium atoms are occupied by deuterium. Complete removal of hydrogen (480 K, 1 Pa) stabilizes a new binary modification (β-MgPd₃, a=391.78(2) pm) crystallizing with a primitive cubic AuCu₃-type structure. Mechanical treatment (grinding) transforms both α and β modifications of MgPd₃ into a cubic face-centered solid solution Mg_0.25Pd_0.75 showing a random distribution of magnesium and palladium atoms.