Es gibt sie doch: Freie Carbinradikale sind bei Raumtemperatur in wässriger Lösung durch die Zersetzung von ein‐ oder dreikernigen Metall(M)‐Komplexen mit Alkylidinliganden zugänglich (siehe Schema; C rot, M blau, H grün). Die Radikale bilden in Lösung durch Kettenverlängerungsreaktionen vielfältige organische Verbindungen. Außerdem können sie Wasserstoff, Sauerstoff oder Kohlenstoff aus dem Lösungsmittel, dem Reaktanten oder dem Produkt abspalten.

They do exist! Free carbyne radicals can be prepared at room temperature in an aqueous solution by the decomposition of mono‐ or trinuclear metal (M) complexes containing alkylidyne ligands (see scheme; red C, blue M, green H). The generated radicals then react to form a variety of organic compounds by chain‐lengthening reactions in solution. They also exhibit hydrogen, oxygen, or carbon abstraction from solvent, reactant, or product molecules.

Ferric ammonium citrate (FAC) is administered to humans in drugs or food supplements, but its exact composition and structural features are not known. We report that the major component in commercial FAC‐brown and FAC‐green is a trinuclear ferric citrate complex, namely [Fe3(cit)4H]6– (1). Complex 1 comprises a dinuclear subunit in which two ferric ions with a 3.122(1) Å separation are bridged by two alkoxido oxygen atoms from two citrate ligands. Two other alkoxido oxygen atoms form a bridge to a third ferric ion completing an Fe3O4 inner core. The compound [Cr(urea)6]2·1·14.5H2O exhibits paramagnetic behavior that corresponds to three magnetically independent high‐spin (HS) d5 and two d3 centers. In addition to complex 1, FAC‐green also contains a dinuclear ferric citrate complex, namely [Fe2(Hcit)3]3–, in an approximate ratio of 1:1.

We study microwave ͑9.36 GHz͒ dissipation in the layered, highly anisotropic superconductors Bi2212 and Bi2223 subjected to a constant magnetic field parallel to the layers. The signal has a characteristic magnetic field dependence, increasing linearly at small fields, reaching a maximum, and decreasing at large fields. We demonstrate experimentally that the microwave absorption is strongly enhanced by application of a low frequency ac magnetic field parallel to the static field. The results are interpreted in the framework of Josephson phase electrodynamics in layered superconductors. In particular, the enhancement is explained as a result of the depinning of the Josephson vortices by the ac field shaking. The theoretical dc field dependence of the microwave absorption for H dc ӷ H ac is in good agreement with experiment. The magnitude of the microwave signal increases rapidly with the anisotropy of the superconductor.

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