We present a Raman spectroscopic investigation of the Herbertsmithite ZnCu3(OH)6Cl2, the first realization of a Heisenberg s = 1/2 antiferromagnet on a perfect kagome lattice. The magnetic excitation spectrum of this compound is dominated by two components, a high temperature quasi elastic signal and a low temperature, broad maximum. The latter has a linear low energy slope and extends to high energy. We have investigated the temperature dependence and symmetry properties of both signals. Our data agree with previous calculations and point to a spin liquid ground state.

A comparison of high-resolution, angle-resolved photoemission spectroscopy (ARPES) data with ab initio band-structure calculations by density functional theory for the anticipated Kondo insulator FeSi shows that the experimental dispersions can quantitatively be described by an itinerant behavior provided that an appropriate self-energy correction is included, whose real part describes the band renormalization due to interactions of the Fe 3d electrons. The imaginary part of the self-energy, on the other hand, determines the linewidth of the quasiparticle peaks in the ARPES data. We use a model self-energy which consistently describes both the renormalized single-particle dispersion and the energy-dependent linewidth of the Fe 3d bands. These results are clear evidence that FeSi is an itinerant semiconductor whose properties can be explained without a local Kondo-like interaction.

The two new pyrazole-based dinucleating ligands 3,5-bis(fluoren-9-ylmethyl)-1H-pyrazole (H 3 L a ) and 3,5-bis(inden-3-ylmethyl)-1H-pyrazole (H 3 L b ) have been prepared and structurally characterized in the case of H 3 L a , and their lithium complexes Li 3 L a and Li 3 L b are reported. These systems can be viewed as coupled dinucleating versions of two widely used Cp fragments bearing pendant amino or amido side chains, which is confirmed by the crystal structure of the solvent-separated ion pair [Li 2 L a (thf) 4 ][Li(thf) 4 ]. In solution, 7 Li NMR spectroscopy indicates the predominant presence of contact ion pairs. The crystal structure of the partially lithiated compound [Li 2 HL a (thf) 5 ] is also presented.

Ni 2 Br 3 ] 3 . Complexes 1a -4a can be described as bimetallic versions of Brookhart-type a-diimine palladium complexes, where dissociation into mononuclear species is prevented by the dinucleating scaffold and the proximate metal ions are suitably positioned to work in concert during substrate transformation. Upon activation of the complexes with MAO and exposure to ethylene, polyethylene is formed. Whereas the palladium complexes display moderate activities, nickel complexes are very active. From structure/activity correlations it is evident that the presence of backbone substitutents at the pyrazolate scaffold as well as bulky ortho aryl substituents is advantageous for polymerisation. Overall, activities of the Ni complexes and the microstructure of the polymer obtained (total branching, T m and molecular weights) are still rather similar to the data reported previously for mononuclear cationic diimine nickel complexes.