Schwefelatome als Liganden in Metall-Komplexen

Surprising Condensation Reactions of the Azadithiolate Cofactor

Azadithiolate, a cofactor found in all [FeFe]-hydrogenases, is shown to undergo acid-catalyzed rearrangement. Fe₂ [(SCH₂ )₂ NH](CO)₆ self-condenses to give Fe₆ [(SCH₂ )₃ N]₂ (CO)₁₇ . The reaction, which is driven by loss of NH₄ ⁺ , illustrates the exchange of the amine group. X-ray crystallography reveals that three Fe₂ (SR)₂ (CO)_x butterfly subunits interconnected by the aminotrithiolate [N(CH₂ S)₃ ]^3- . Mechanistic studies reveal that Fe₂ [(SCH₂ )₂ NR](CO)₆ participate in a range of amine exchange reactions, enabling new methodologies for modifying the adt cofactor. Ru₂ [(SCH₂ )₂ NH](CO)₆ also rearranges, but proceeds further to give derivatives with Ru-alkyl bonds Ru₆ [(SCH₂ )₃ N][(SCH₂ )₂ NCH₂ ]S(CO)₁₇ and [Ru₂ [(SCH₂ )₂ NCH₂ ](CO)₅ ]₂ S.

Stability, Structure and Reconstruction of 1H-Edges in MoS2

Density functional studies of the edges of single-layer 1H-MoS₂ are presented. This phase presents a rich variability of edges that can influence the morphology and properties of MoS₂ nano-objects, play an important role in industrial chemical processes, and find future applications in energy storage, electronics and spintronics. The so-called Mo-100 %S edges vertical S-dimers were confirmed to be stable, however the authors also identified a family of metastable edges combining Mo atoms linked by two-electron donor symmetrical disulfide ligands and four-electron donor unsymmetrical disulfide ligands. These may be entropically favored, potentially stabilizing them at high temperatures as a "liquid edge" phase. For Mo-50 %S edges, S-bridge structures with 3× periodicity along the edge are the most stable, compatible with a Peierls' distortion arising from the d-bands of the edge Mo atoms. An additional explanation for this periodicity is proposed through the formation of 3-center bonds.

Structural rearrangements in triple-decker-like complexes with mixed group 15/16 ligands: synthesis and characterization of the redox couple

The reaction of As4Se4 with stoichiometric amounts of [Cp*Fe2(CO)4] (Cp* = C5Me5) in boiling toluene forms [Cp2*Fe2As2Se2] (1) in good yield. X-ray crystallography shows 1 to have a triple-decker structure which comprises a tetraatomic mu,eta4:4-As2Se2 ligand. Density functional theory (DFT) and extended Hückel molecular orbital (EHMO) calculations confirm that the As2Se2 ligand behaves as a four-electron pi donor. Oxidation of 1 with equimolar amounts of [(C5H5)2Fe]PF6, Br2 and I2, respectively, gave compounds 2-4. According to X-ray crystallographic investigations that were carried out on 2 and 4, the oxidation state has a considerable influence on the structure of the Fe2As2Se2 core: significant shortening of the Fe-Fe distance (deltad(Fe-Fe)> 0.3 A) and weakening of the As-As bond length ((deltad(As-As) > 0.3 A) suggests the formal presence of two diatomic AsSe ligands and a Fe-Fe bond. DFT and EHMO calculations confirm that an electron is removed from an occupied Fe-Fe orbital of antibonding character during oxidation. All molecular orbitals lower their energies upon oxidation, but the energy drop is relatively small for those involving the As-As bond. An additional structural feature in 4 consists of an electronic interaction of the iodide with both As atoms which suggests a formally neutral ion pair. Electrochemical studies confirm that the oxidation of 1 is a reversible one-electron process with E(1/2)= +0.07 V (in THF). These studies also reveal that 4 dissociates in polar solvents, such as THF, into [1]+ and I-, which is followed by transformation into 1 and I3.