New complexes (Bu4N)2[Mo6X8(n-C3F7COO)6] (X = Br, I) display extraordinarily bright long-lived red phosphorescence both in solution and solid phases, with the highest emission quantum yields and the longest emission lifetimes among hexanuclear metal cluster complexes of Mo, W and Re, hitherto reported

Highly luminescent complexes [Mo6X8(n-C3F7COO)6]2- (X=Br, I).

Mid- to high-valent imido and nitrido complexes of iron

Synthetic iron–sulfur clusters of general formulation [FemSqLl]z with core atoms Fe and S and terminal ligands L constitute a family of molecular clusters with remarkably diverse geometrical and electronic structures. Several structure types are also found in proteins. The large majority of research on these clusters has involved elucidation of physical properties. Here, we direct attention to reactivity in the form of cluster conversions in which the FemSq cores of reactants are transformed to new structures, usually of different nuclearity, in overall reactions such as self-assembly and fragment condensation and dissociation. An extensive body of core conversions, many of which have not been recognized as such, are presented including those in biological systems. All structural core types are depicted, and all core conversions are diagrammatically summarized. Clusters containing the cubane-type Fe4S4 core play a central role in conversion chemistry. The core conversion concept tends to reinforce the des...

Structural Conversions of Synthetic and Protein-Bound Iron–Sulfur Clusters

Biological nitrogen fixation, an essential process of the biogeochemical nitrogen cycle that supports life on Earth, is catalyzed by the nitrogenase enzyme. The nitrogenase active site contains an iron and molybdenum cofactor (FeMo-co) composed of 7Fe-9S-Mo-homocitrate and one not-yet-identified atom, which probably is the most complex [Fe–S] cluster in nature. Here, we show the in vitro synthesis of FeMo-co from its simple constituents, Fe, S, Mo, and homocitrate. The in vitro FeMo-co synthesis requires purified NifB and depends on S-adenosylmethionine, indicating that radical chemistry is required during FeMo-co assembly.

https://www.pnas.org/content/pnas/103/14/5297.full.pdf

NifB-dependent in vitro synthesis of the iron-molybdenum cofactor of nitrogenase.

The iron-molybdenum cofactor (FeMoco) of the nitrogenase MoFe protein is a highly complex metallocluster that provides the catalytically essential site for biological nitrogen fixation. FeMoco is assembled outside the MoFe protein in a stepwise process requiring several components, including NifB-co, an iron- and sulfur-containing FeMoco precursor, and NifEN, an intermediary assembly protein on which NifB-co is presumably converted to FeMoco. Through the comparison of Azotobacter vinelandii strains expressing the NifEN protein in the presence or absence of the nifB gene, the structure of a NifEN-bound FeMoco precursor has been analyzed by x-ray absorption spectroscopy. The results provide physical evidence to support a mechanism for FeMoco biosynthesis. The NifEN-bound precursor is found to be a molybdenum-free analog of FeMoco and not one of the more commonly suggested cluster types based on a standard [4Fe-4S] architecture. A facile scheme by which FeMoco and alternative, non-molybdenum-containing nitrogenase cofactors are constructed from this common precursor is presented that has important implications for the biosynthesis and biomimetic chemical synthesis of FeMoco.

https://www.pnas.org/content/pnas/103/5/1238.full.pdf

Structural insights into a protein-bound iron-molybdenum cofactor precursor.

The Chemistry of Synthetic Fe–Mo–S Clusters and their Relevance to the Structure and Function of the Fe–Mo–S Center in Nitrogenase

Preparation of tetrabutylammonium octa-μ3-bromohexa(trifluoromethanesulfonato)octahedro-hexamolybdate (2−), (Bu4N)2[Mo6Br8i(CF3SO3)6a] and other derivatives containing the Mo6Br84+ core

Steven M. Malinak

Papers

The Chemistry of Synthetic Fe–Mo–S Clusters and their Relevance to the Structure and Function of the Fe–Mo–S Center in Nitrogenase

Preparation of tetrabutylammonium octa-μ3-bromohexa(trifluoromethanesulfonato)octahedro-hexamolybdate (2−), (Bu4N)2[Mo6Br8i(CF3SO3)6a] and other derivatives containing the Mo6Br84+ core