We report the magnetoresistance (MR), Hall effect, and de Haas-van Alphen (dHvA) effect studies of single crystals of tungsten carbide, WC, which is predicted to be a new type of topological semimetal with triply degenerate nodes. With the magnetic field rotated in the plane perpendicular to the current, WC shows a field induced metal-to-insulator-like transition and large nonsaturating quadratic MR at low temperatures. As the magnetic field parallel to the current, a pronounced negative longitudinal MR only can be observed for the certain direction of current flow. Hall effect indicates WC is a perfect compensated semimetal, which may be related to the large nonsaturating quadratic MR. The analysis of dHvA oscillations reveals that WC is a multiband system with small cross-sectional areas of Fermi surface and light cyclotron effective masses. Our results indicate that WC is an ideal platform to study the recently proposed "New Fermions" with triply degenerate crossing points.

The copper-catalyzed oxidative homocoupling of terminal alkynes has been studied with DFT methods. The role of Cu(I) or Cu(II) as the initial oxidation state as well as the effect of the changes in the substrate and the base have been examined. Oxidants responsible for outer-and inner-sphere electron transfer processes have also been investigated. The Cu/O 2 interactions, which arise when dioxygen is employed as the oxidant, have been studied explicitly to fully describe the 4-electron reduction process, providing a plausible mechanism that could serve as a model for other aerobic oxidative couplings. The obtained results completely agree with the reported experimental data: the computed free energy barriers are low enough for the reactions to proceed at room temperature, and electron-poor alkynes and stronger bases lead to faster reactions.

An excess of bis-1,3-(4-iodophenyl)bicyclo[1.1.1]pentane, prepared in 63 % yield by iodination of 1,3-diphenylbicyclo[1.1.1]pentane, was selectively mono-coupled with 9-ethynyl-1,5-dimethoxy-10-phenylethynylanthracene (26), and subsequently with the zinc derivatives of 1-(2-methyl/methoxy-4-methyl-5-phenylthiophen-3-yl)-2-(2-methyl/methoxy-4-methylthiophen-3-yl)perfluorocyclopentenes (38-H-41-H). Regioselective synthesis of the 2-unsubstituted thiophenes 38-H-41-H required intermediate preparation of 2-trimethylsilyl-3,5-dimethyl-4-bromothiophene (37) or 2-trimethylsilyl-5-methoxy-3-methyl-4-bromothiophene (40). Protection of the alpha-position of the thiophene ring with a 2-trimethylsilyl group blocks the rearrangement of the 4-lithio derivatives into the corresponding 2-lithiated thiophenes. With the bicyclo[1.1.1]pentane fragment linking the photochromic units 1-3 and 1,5-dimethoxy-9,10-di(phenylethynyl)anthracene as a fluorescent part, quantitative resonance energy transfer between the excited state of the fluorophore (donor) and the closed form of the photochromic units 1-3 (acceptors) was observed. The closed forms of the methoxy-substituted photochromic units 2 and 3 are less resistant to UV light (313 nm) than the closed form of 1.

Stoichiometric LiBC has been synthesized using both arc melting and sealed tantalum ampoule methods. Hole-doped Li 1Ϫx BC ͑0Ͻxр0.37͒ compounds have been realized through vacuum deintercalation from LiBC. The hexagonal crystal lattice has remained largely intact, with only slight decreases in lattice parameters upon hole-doping. The samples are intrinsically diamagnetic and are semiconducting in the 2-300 K range studied. Increased hole-doping leads to a color darkening as well as a decrease in resistivity.