Cheu-Pyeng Cheng

The reaction between unsaturated tetrarhenium cluster H4Re4(CO)12 and tris(diphenylphosphino)methane

Abstract The reaction between the unsaturated cluster H 4 Re 4 (CO) 12 and tripod (HC(PPh 2 ) 3 ) was investigated. After refluxing the reactants in CH 2 Cl 2 for 8 h, four compounds were isolated. They are identified by NMR, mass, IR and elemental analysis to be HRe(CO) 3 (η 2 - tripod), H 2 Re 2 (CO) 6 (η 3 -μ 2 -tripod), H 3 Re 3 (CO) 9 (η 3 -μ 3 -tripod) and H 4 Re 4 (CO) 12 (η 3 - μ 3 -tripod). The structures of the trirhenium and tetrarhenium cluster products were determined by X-ray diffraction method. In H 3 Re 3 (CO) 9 (tripod), the tripod ligand is capping on top of the Re 3 plane. The three rhenium atoms and the three phosphorus atoms form a slightly distorted trigonal prism. Though the ReRe and ReP bond distances show the presence of steric strain, H 3 Re 3 (CO) 9 (tripod) is thermally much more stable than the uncapped H 3 Re 3 (CO) 12 . In H 4 Re 4 (CO) 12 (tripod), the four rhenium atoms form a spiked triangular configuration. Re4 is bonded to Re1 and is nearly perpendicular to the Re1Re2Re3 triangle. The three phosphorus atoms are coordinated to Re2, Re3 and Re4. A novel feature of this tetranuclear cluster is that one of the phenyl groups is coordinated in η 2 -fashion through a double bond to Re4 which is in the spiked position. This is the first example of phenyl group coordination in tripod chemistry. The tetra rhenium cluster is also stable in refluxing CH 2 Cl 2 in the presence of tripod.

119Sn NMR studies on alloying silica supported tin with nickel and palladium

Abstract Catalysts of Sn SiO 2 , Sn-Ni Si0 2 , and Sn-Pd SiO 2 were prepared with the incipient wetness method. The Knight shift in the 119Sn NMR absorption peaks from these catalysts as well as a sample of powdered tin metal were monitored by the solid state NMR spectroscopy. The peaks from the tin powders and the tin on the Sn SiO 2 catalyst were anisotropic with the Knight shifts at 0.755% (ktt) and 0.813% (K11). The Knight shift of tin was changed on alloying the supported tin with nickel or palladium. These changes in the Knight shift suggested that the electronic properties of the tin atoms in the supported alloys were affected by the presence of nickel and palladium.

PRODUCTION OF CARBON NANOTUBES IN AIR

Carbon nanotubes were produced by plasma discharging of graphite electrodes in air at 1 atm. The combined yield of CNTs and carbon nanoparticles is ∼20 wt % relative to the mass of cathode deposits or 14 wt% of graphite electrode consumed. The yields of CNTs and carbon nanoparticles under different inert gas atmospheres, such as He, Ar, N2, and air were compared.