New type dithiolene complex based on 4,5-(1,4-dioxane-2,3-diyldithio)-1,3-dithiol ligand: Synthesis,experimental and theoretical investigation

A new Nickel complex with an extended multisulfur dithiolene ligand Ni(edodddt)₂ (edodddt = 2,3,4α,8α-tetrahydro-dithiine [2,3-b] [1,4] dioxo-6,7-dithiolene) has been synthesized and characterized by electrochemical measurements, IR, UV–Vis and NMR spectroscopy. Its crystal structure was resolved by X-ray diffraction on a single crystal. DFT calculations were made in order to compare the results with the experimental findings and gain an insight of the properties of this new dithiolene complex.     

Electron tomography and computer visualisation of a three-dimensional 'photonic' crystal in a butterfly wing-scale

A combination of transmission electron tomography and computer modelling has been used to determine the three-dimensional structure of the photonic crystals found in the wing-scales of the Kaiser-I-Hind butterfly (Teinopalpus imperialis). These scales presented challenges for electron microscopy because the periodicity of the structure was comparable to the thickness of a section and because of the complex connectivity of the object. The structure obtained has been confirmed by taking slices of the three-dimensional computer model constructed from the tomography and comparing these with transmission electron microscope (TEM) images of microtomed sections of the actual scale. The crystal was found to have chiral tetrahedral repeating units packed in a triclinic lattice.     

The design of a continuous reactor for fluorous biphasic reactions under pressure and its use in alkene hydroformylation

A reactor, into which all reagents can be fed continuously and from which the reaction mixture can be continuously removed to a gravity separator, where product can be continuously removed and the catalyst phase recycled to the reactor, has been constructed and used for the hydroformylation of alkenes in fluorocarbon solvents.     

Competitive paths for methanol decomposition on Pt(111)

Periodic, self-consistent, Density Functional Theory (PW91-GGA) calculations are used to study competitive paths for the decomposition of methanol on Pt(111). Pathways proceeding through initial C-H and C-O bond scission events in methanol are considered, and the results are compared to data for a pathway proceeding through an initial O-H scission event [Greeley et al. J. Am. Chem. Soc. 2002, 124, 7193]. The DFT results suggest that methanol decomposition via CH(2)OH and either formaldehyde or HCOH intermediates is an energetically feasible pathway; O-H scission to CH(3)O, followed by sequential dehydrogenation, may be another realistic route. Microkinetic modeling based on the first-principles results shows that, under realistic reaction conditions, C-H scission in methanol is the initial decomposition step with the highest net rate. The elementary steps of all reaction pathways (with the exception of C-O scission) follow a linear correlation between the transition state and final state energies. Simulated HREELS spectra of the intermediates show good agreement with available experimental data, and HREELS spectra of experimentally elusive reaction intermediates are predicted.     

Characterisation of zeolitic materials with a HEU-type structure modified by transition metal elements: definition of acid sites in nickel-loaded crystals in the light of experimental and quantum-chemical results

Nickel-loaded HEU-type zeolite crystals have been obtained by well-known synthetic procedures and characterised by X-ray fluorescence (XRF), scanning-electron microscopy/ energy-dispersive spectroscopy (SEM-EDS), FT-IR, diffuse reflectance UV/ Vis spectroscopy (DR(UV/Vis)S) and X-ray photoelectron spectroscopy (XPS) measurements as non-homoionic and non-stoichiometric substances containing exchangeable hydrated Ni2+ ions in the micropores and nickel hydroxide phases supported on the surface. Thermogravimetric analysis/differential gravimetry (TGA/DTG) and differential thermal analysis (DTA) demonstrated that full dehydration below approximately 400 degrees C follows a clearly endothermic process, whereas at higher temperatures the zeolite is amorphised and finally partially recrystallised to Ni(Al,Si) oxides, detected by powder X-ray powder diffraction (XRD). The solid acidity of NiHEU, initially determined by temperature-programmed desorption (TPD) of ammonia to be 8.93 mgg(-1) NH3, is attributed to the weak acid sites (fundamentally Lewis sites) resolved at approximately 183 degrees C, and to the strong acid sites (essentially Br?nsted sites) resolved at approximately 461 degrees C in the TPD pattern. A more sophisticated study based on in situ/ex situ FT-IR with in situ/ex situ 27Al MAS NMR and pyridine (Py) as a probe molecule, revealed that the Lewis acid sites can be attributed primarily to Ni2+ ions, whereas the Br?nsted ones can probably be associated with the surface-supported nickel hydroxide phases. The spectroscopic measurements in conjunction with powder XRD and 29Si MAS NMR data strongly suggest that distorted Al tetrahedra are formed during the dehydration process and Py chemisorption/complexation (NiHEU-Py), whereas the crystal structure is remarkably well preserved in the rehydrated material (NiHEU-Py/R). The structural, electronic, energetic and spectroscopic properties of all possible nickel(II) aqua and dihydroxy complexes absorbed in the zeolite micropores or supported on the zeolite surface were studied theoretically by density functional theory (DFT). The computed proton affinity, found to be in the range 182.0-210.0 kcalmol(-1), increases with increasing coordination number of the aqua and dihydroxy nickel(II) complexes.     

A Cu/Pt near-surface alloy for water-gas shift catalysis

The primary route to hydrogen production from fossil fuels involves the water-gas shift (WGS) reaction, and an improvement in the efficiency of WGS catalysts could therefore lead to a major leap forward in the realization of hydrogen economy. On the basis of a combination of high-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations, we suggest the existence of a new thermodynamically stable Cu/Pt near-surface alloy (NSA). Temperature-programmed desorption and DFT reveal that this Cu/Pt NSA binds CO significantly more weakly than does Pt alone, thereby implying a considerable reduction in the potential for CO poisoning of the Cu/Pt NSA surface as compared to that of pure Pt. In addition, DFT calculations show that this Cu/Pt NSA is able to activate H2O easily, which is the rate-determining step for the WGS on several metal surfaces, and, at the same time, to bind the products of that reaction and formate intermediates rather weakly, thus avoiding possible poisoning of the catalyst surface. The Cu/Pt NSA is thus a promising candidate for an improved WGS catalyst.