Automated search for new thermoelectric materials: the case of LiZnSb

An automated band structure calculation based on the inorganic crystal structure database and the augmented plane wave method for electronic structure calculations is presented. Using a rigid band approach and semiclassic Boltzmann theory the band structures are analyzed and a large number of compounds are screened for potential interesting thermoelectric properties. We thereby propose LiZnSb as a potential new thermoelectric material. The k-space structure of the lowest conduction band of LiZnSb is analyzed in detail, and excellent thermoelectric properties are expected for this material. Furthermore the lattice dynamics are calculated, and anisotropic lattice thermal conduction is predicted.     

Production of slow protonium in vacuum

We descrbe how protonium, the quasi-stable antiproton-proton bound system, has been synthesized following the interaction of antiprotons with the molecular ion in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events in the ATHENA experiment, evidence is presented for protonium production with sub-eV kinetic energies in states around n = 70, with low angular momenta. This work provides a new two-body system for studies using laser spectroscopic techniques.      

Iridium‐Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols with the Liberation of Syngas

A new iridium ‐ catalyzed reaction in which molecular hydrogen and carbon monoxide are cleaved from primary alcohols in the absence of any stoichiometric additives has been developed. The dehydrogenative decarbonylation was achieved with a catalyst generated in situ from [Ir(coe)₂Cl]₂ (coe=cyclooctene) and racemic 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (rac‐BINAP) in a mesitylene solution saturated with water. A catalytic amount of lithium chloride was also added to improve the catalyst turnover. The reaction has been applied to a variety of primary alcohols and gives rise to products in good to excellent yields. Ethers, esters, imides, and aryl halides are stable under the reaction conditions, whereas olefins are partially saturated. The reaction is believed to proceed by two consecutive organometallic transformations that are catalyzed by the same iridium(I)–BINAP species. First, dehydrogenation of the primary alcohol to the corresponding aldehyde takes place, which is then followed by decarbonylation to the product with one less carbon atom.     

Mechanistic investigation of the iridium-catalysed alkylation of amines with alcohols

The [Cp*IrCl(2)](2)-catalysed alkylation of amines with alcohols was investigated using a combination of experimental and theoretical methods. A Hammett study involving a series of para-substituted benzyl alcohols resulted in a line with a negative slope. This clearly documents that a positive charge is built up in the transition state, which in combination with the measurement of a significant kinetic isotope effect determines hydride abstraction as being the selectivity-determining step under these conditions. A complementary Hammett study using para-substituted anilines was also carried out. Again, a line with a negative slope was obtained suggesting that nucleophilic attack on the aldehyde is selectivity-determining. A computational investigation of the entire catalytic cycle with full-sized ligands and substrates was performed using density functional theory. The results suggest a catalytic cycle where the intermediate aldehyde stays coordinated to the iridium catalyst and reacts with the amine to give a hemiaminal which is also bound to the catalyst. Dehydration to the imine and reduction to the product amine also takes place without breaking the coordination to the catalyst. The fact that the entire catalytic cycle takes place with all the intermediates bound to the catalyst is important for the further development of this synthetic transformation.     

Rigidity of certain finite group actions on the complex projective plane

Partially supported by NSERC grant A4000     

A study of the sump beaver's dental enamel

The nature of the iron-containing phase in the dental enamel of sump beaver incisors has been studied by use of Mössbauer spectroscopy. All iron atoms are found to be trivalent and to be present in particles exhibiting superparamagnetic relaxation. The iron-containing phase has Mössbauer parameters similar to those of ferritin.