The Kondo effect arises due to the interaction between a localized spin and the electrons of a surrounding host. Studies of individual magnetic impurities by scanning tunneling spectroscopy have renewed interest in Kondo physics; however, a quantitative comparison with theoretical predictions remained challenging. Here we show that the zero-bias anomaly detected on an organic radical weakly coupled to a Au (111) surface can be described with astonishing agreement by perturbation theory as originally developed by Kondo 60 years ago. Our results demonstrate that Kondo physics can only be fully conceived by studying both temperature and magnetic field dependence of the resonance. The identification of a spin 1/2 Kondo system is of relevance not only as a benchmark for predictions for Kondo physics but also for correlated electron materials in general.

[Ru(II)(terpy)(DMSO)Cl(2)] complexes were synthesized as a 5/1 mixture of cis and trans isomers, and their reactivities with CO and with substituted 2,2':6',2' '-terpyridine (terpy) moieties have been investigated. The structure of a trans isomer and its CO adduct have been unambiguously assigned by spectroscopy and X-ray diffraction. The [Ru(terpy)(terpy-Br)](2+) complex prepared either from the cis-[Ru(II)(terpy)(DMSO)Cl(2)] or from the cis-[Ru(II)(terpy-Br)(DMSO)Cl(2)] precursor appeared to be reactive in cross-coupling reactions promoted by low-valent palladium(0) and is an attractive target for the stepwise synthesis of polynuclear complexes bearing vacant coordination sites (terpy-Br for 4'-bromo-2,2':6',2' '-terpyridine). Several bipyridine, phenanthroline, and bipyrimidine complexes were prepared this way and their optical and redox properties determined and discussed.

A nitronyl-nitroxide (NIT) biradical D-NIT2 linked by a single double bond has been engineered and investigated in the solid state by a combination of X-ray diffraction, magnetic susceptibility measurement, EPR, as well as solid-state (1)H and (13)C NMR spectroscopies, and experimental electron density distribution. All techniques reveal that a double bond is a very efficient coupling unit for exchange interactions between two radical moieties. Using a Bleaney-Bowers model dimer (H = -JS(1)S(2)), a singlet-triplet energy gap of J = -460 K was found with the singlet state being the ground state. This very strong intramolecular interaction was confirmed by EPR measurements in CH(2)Cl(2) solution (6 10(-4) M) or dispersed in a polymer matrix at low concentration. In keeping with these unusual interactions, solid-state NMR signals of the biradical were found to be considerably less shifted than those found for related monoradicals. Temperature-dependent solid-state (13)C NMR spectra of D-NIT2 confirmed the very strong intramolecular coupling constant (J = -504 K). The electron density distribution of D-NIT2 was measured by high resolution X-ray diffraction, which also revealed that this biradical is an ideally conjugated system. The in-depth characterization includes the deformation maps and the observed electron density ellipticities, which exhibit a pronounced sigma-pi character of the O-N-C=C-N-O cores in keeping with an efficient electronic delocalization along the alkene spacer.