CHEMISTRY: A Question of Geometry

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Science  20 Jun 2008:
Vol. 320, Issue 5883, pp. 1565b
DOI: 10.1126/science.320.5883.1565b

The varied metal clusters that proteins use to handle diatomic gases are remarkable not only for the unsurpassed chemistry they support but also for the fine tuning of the geometric properties of the metal atoms by their ligands. By synthesizing a series of dinuclear FeNi complexes, Ohki et al. demonstrate how the Ni can be switched between octahedral, square pyramidal, and square planar geometries. In the precursor compound, the Fe atom carries three CO ligands, there are three bridging thiolates, and the Ni adopts a slightly distorted square pyramidal structure. Adding a bidentate thioether-thiolate ligand onto the Ni atom resulted in the release of one of the bridging thiolates and a square planar configuration. In contrast, adding a phenolate-thioether ligand yielded an octahedral Ni that retained the three Ni-μ-S bonds, with Ni-O and Ni-S links to the bidentate ligand and a Ni-O bond to a molecule of solvent (methanol). The reversible loss of methanol was accompanied by ejection of one of the bridging thiolates and conversion into the square planar configuration. Integrating these findings with earlier work on the [NiFe] hydrogenase and other dinuclear complexes (NiRu and GeRu), these authors propose that the hydrogenase NiFe cluster binds H2 by shifting the square pyramidal Ni into an octahedral configuration and that heterolysis of H2 leads to loss of the bridging OH ligand as H2O. — GJC

Proc. Natl. Acad. Sci. U.S.A. 105, 7652 (2008).

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