A diuranium carbide cluster stabilized inside a C80 fullerene cage.

Unsupported non-bridged uranium-carbon double bonds have long been sought after in actinide chemistry as fundamental synthetic targets in the study of actinide-ligand multiple bonding. Here we report that, utilizing Ih(7)-C80 fullerenes as nanocontainers, a diuranium carbide cluster, U=C=U, has been encapsulated and stabilized in the form of UCU@Ih(7)-C80. This endohedral fullerene was prepared utilizing the Krätschmer-Huffman arc discharge method, and was then co-crystallized with nickel(II) octaethylporphyrin (NiII-OEP) to produce UCU@Ih(7)-C80·[NiII-OEP] as single crystals. X-ray diffraction analysis reveals a cage-stabilized, carbide-bridged, bent UCU cluster with unexpectedly short uranium-carbon distances (2.03 Å) indicative of covalent U=C double-bond character. The quantum-chemical results suggest that both U atoms in the UCU unit have formal oxidation state of +5. The structural features of UCU@Ih(7)-C80 and the covalent nature of the U(f1)=C double bonds were further affirmed through various spectroscopic and theoretical analyses

On the Upper Limits of Oxidation States in Chemistry.

The concept of oxidation state (OS) is based on the concept of Lewis electron pairs, in which the bonding electrons are assigned to the more electronegative element. This approach is useful for keeping track of the electrons, predicting chemical trends, and guiding syntheses. Experimental and quantum-chemical results reveal a limit near +8 for the highest OS in stable neutral chemical substances under ambient conditions. OS=+9 was observed for the isolated [IrO4 ]+ cation in vacuum. The prediction of OS=+10 for isolated [PtO4 ]2+ cations is confirmed computationally for low temperatures only, but hasn't yet been experimentally verified. For high OS species, oxidation of the ligands, for example, of O-2 with formation of . O-1 and O-O bonds, and partial reduction of the metal center may be favorable, possibly leading to non-Lewis type structures

On the Upper Limits of Oxidation States in Chemistry.

The concept of oxidation state (OS) is based on the concept of Lewis electron pairs, in which the bonding electrons are assigned to the more electronegative element. This approach is useful for keeping track of the electrons, predicting chemical trends, and guiding syntheses. Experimental and quantum-chemical results reveal a limit near +8 for the highest OS in stable neutral chemical substances under ambient conditions. OS=+9 was observed for the isolated [IrO4 ]+ cation in vacuum. The prediction of OS=+10 for isolated [PtO4 ]2+ cations is confirmed computationally for low temperatures only, but hasn't yet been experimentally verified. For high OS species, oxidation of the ligands, for example, of O-2 with formation of . O-1 and O-O bonds, and partial reduction of the metal center may be favorable, possibly leading to non-Lewis type structures

Six questions on topology in theoretical chemistry

International audienceThe paper collects the answers of the authors to the following questions:• What is the significance of topological approach?• Can new chemical concepts be found by a topological approach?• What is the status of a chemical concept within a topological approach?• Should topological approaches provide measurable quantities?• Is it possible to predict the outcome of a topological approach without performing a calculation on a computer?• What are new domains for which topological approaches would be useful