1,2-Dibromoethane on Cu(100): bonding structure and transformation to C2H4

Temperature-programmed reaction/desorption, mass spectrometry, reflection-absorption infrared spectroscopy, x-ray photoelectron spectroscopy, and density functional theory calculations have been employed to explore the reaction and bonding structure of 1,2-C(2)H(4)Br(2) on Cu(100). Both the trans and gauche conformers are found to dissociate by breaking the C-Br bonds on clean Cu(100) at 115 K, forming C(2)H(4) and Br atoms. Theoretical investigations for the possible paths of 1,2-C(2)H(4)Br(2) → C(2)H(4) + 2Br on Cu(100) suggest that the barriers of the trans and gauche molecules are in the ranges of 0-4.2 and 0-6.5 kcal/mol, respectively. The C-Br scission temperature of C(2)H(4)Br(2) is much lower than that (~170 K) of C(2)H(5)Br on Cu(100). Adsorbed Br atoms can decrease the dissociation rate of the 1,2-C(2)H(4)Br(2) molecules impinging the surface. The 1,2-C(2)H(4)Br(2) molecules adsorbed in the first monolayer are structurally distorted. Both the trans and gauche molecules exist in the second monolayer, but with no preferential adsorption orientation. However, the trans molecule is the predominant species in the third or higher layer formed at 115 K. The layer structure is not thermally stable. Upon heating the surface to 150 K, the orientation of the trans 1,2-C(2)H(4)Br(2) molecules in the layer changes, leading to the rotation of the BrCCBr skeletal plane toward the surface normal on average and the considerable growth of the CH(2) scissoring peak. On oxygen-precovered Cu(100), decomposition of 1,2-C(2)H(4)Br(2) to form C(2)H(4) is hampered and no oxygenated hydrocarbons are formed. The presence of the oxygen atoms also increases the adsorption energy of the second-layer molecules.     

Synthesis of Lithiophorite in High Alkaline Conditions

Lithiophorite consists of alternatively stacked MnO₆ octahedral sheets and LiAl₂(OH)₆ octahedral sheets. Its applications in laboratories and industries have been hindered by sophisticated operation procedures, long reaction time, or impurities existing in the final product. We proposed a fast and simple method, mixing birnessite, aluminate and lithium hydroxide together (designated it as the BAL method) in high alkaline conditions (pH > 13), and treating it hydrothermally at 423 K for 6 hours to prepare pure lithiophorite. A specific reaction between lithium cations and aluminate anions plays as a key role in the BAL method. Due to this specific reaction, Li_xAl_n(OH)_m^+z complexed cations can form and penetrate into interlayers of birnessite to replace sodium cations. In high alkaline conditions (pH > 12), Li_xAl_n(OH)_m^+z complexed cations become smaller and are soluble. Thus, the higher alkaline Li_xAl_n(OH)_m^+z complexed cations can penetrate into interlayers of birnessite at a higher rate. Furthermore, impurities, such as lithium intercalated gibbsite (LIG), aluminum oxyhydroxides and aluminum hydroxides are not stable in high alkaline conditions. Consequently, pure lithiophorite can be easily obtained within 6 hours in high alkaline conditions.     

Organotransition-Metal Complexes of Multidentate Ligands 3. The Unexpected Derivatives of Bis(3,5-Dimethylpyrazol-1-YL)Methanetetracarbonylmolybdenlim(0) and-Tungsten(0) Complexes

Thermolysis of (H₂CPz′₂)M(CO)₄ (H₂CPz′₂ = bis(3,5-dimethylpyrazol-1-yl)methane; M=Mo, W) in 1,2-dimethoxyethane did not give the expected 16-electron complexes, (H₂CPz′₂)M(CO)₃, but gave dinuclear compounds, [(H₂CPz′₂)M(CO)₃]₂, probably containing two linear carbonyl bridges and no metal-metal interactions. The dimers reacted with CH₃CN to give mononuclear compounds, (H₂CPz′₂)M(CO)₃(NCCH₃), identical to the substitution products between (H₂CPz′₂)M(CO)₄ and CH₃CN.     

Normal Components, Kekulé Patterns, and Clar Patterns in Plane Bipartite Graphs

As a general case of molecular graphs of polycyclic alternant hydrocarbons, we consider a plane bipartite graph G with a Kekulé pattern (perfect matching). An edge of G is called nonfixed if it belongs to some, but not all, perfect matchings of G. Several criteria in terms of resonant cells for determining whether G is elementary (i.e., without fixed edges) are reviewed. By applying perfect matching theory developed in plane bipartite graphs, in a unified and simpler way we study the decomposition of plane bipartite graphs with fixed edges into normal components, which is shown useful for resonance theory, in particular, cell and sextet polynomials. Further correspondence between the Kekulé patterns and Clar (resonant) patterns are revealed.     

Counting Sums of Three Squares

Let (x) be the error term associated with the asymptotic formulafor the counting function on the set of numbers that are sumsof three squares. We give a formula for (x) and use it to provethat (x) has average order and normal order 3 1og x/(16 1og2).     

Plasmonic Bloch oscillations in cylindrical metal-dielectric waveguide arrays

This study investigates plasmonic Bloch oscillations (PBOs) in cylindrical metal-dielectric waveguide arrays (MDWAs) by performing numerical simulations and theoretical analyses. Optical conformal mapping is used to transform cylindrical MDWAs into equivalent chirped structures with permittivity and permeability gradients across the waveguide arrays, which is caused by the curvature of the cylindrical waveguide. The PBOs are attributed to the transformed structure. The period of oscillation increases with the wavelength of the incident Gaussian beam. However, the amplitude of oscillation is almost independent of wavelength.     

Effect of complex formation on the half wave potentials of redox active ligands

A general equation is derived for the shift in half wave potential, ΔE , for ligand reduction on complexation with a metal. The formation of several complexes with differing stoichiometry and protonation states is considered explicitly. The dependence of ΔE on metal ion concentration, holding the ligand concentration constant, can be used to determine stability constants or their ratios. The meaning of ΔE depends on the stoichiometric changes following ligand oxidation state change, in a manner analogous to the case where the metal is the redox site.     

Electron-transfer properties of different carbon nanotube materials,and their use in glucose biosensors

Different types of carbon nanotube material (single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) of different internal diameter) have been used for preparation of CNT-modified glassy-carbon electrodes. Redox reactions involving ferricyanide and hydrogen peroxide were examined at the CNT-modified electrodes. Electrodes modified with SWCNTs usually had better electron-transfer properties than MWCNT-modified electrodes. Glucose biosensors were also prepared with electropolymerized polyphenylenediamine films, CNT materials, and glucose oxidase. Amperometric behavior in glucose determination was examined. SWCNT-modified glucose biosensors usually had a wider dynamic range (from 0.1 to 5.5 mmol L⁻¹) and greater sensitivity in glucose determination. The detection limit was estimated to be 0.05 mmol L⁻¹.