Chemists have long sought to mimic enzymatic hydrogen activation with structurally simpler compounds. Here, we report a functional [NiFe]-based model of [NiFe]hydrogenase enzymes. This complex heterolytically activates hydrogen to form a hydride complex that is capable of reducing substrates by either hydride ion or electron transfer. Structural investigations were performed by a range of techniques, including x-ray diffraction and neutron scattering, resulting in crystal structures and the finding that the hydrido ligand is predominantly associated with the Fe center. The ligand's hydridic character is manifested in its reactivity with strong acid to liberate H(2).

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The 4f electronic state and the decay process of the photoexcited 4d'4f "+' states in CeO, are investigated by means of a resonant photoemission technique in the Ce 41~4f photoabsorption region. Resonant enhancement of the valence-band emission is clearly observed in the giant-absorption region. This confirms the existence of the 4f electron in the ground state of CeO, . The 4f-derived emission exhibits a single-peak distribution rather than a double-peak structure such as observed in other Ce compounds.The Ce Sp emission band, which spreads over about 10 eV and consists of at least three or more fine structures, also shows the resonant enhancement in the giant-absorption region. In the prethreshold region, the Ce Sp fine structures as we11 as the 4f emission band show enhancements, but these constantinitial-state spectra are different from each other. The obtained results are discussed in terms of the mixed valence in the ground state of Ce02 and of possible intermediate configurations in the resonant photoemission process.

The pH-dependent hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes and hydrogenation of the carbonyl compounds have been investigated with water-soluble bis(mu-thiolate)(mu-hydride)NiRu complexes, Ni(II)(mu-SR)(2)(mu-H)Ru(II) {(mu-SR)(2) = N,N'-dimethyl-N,N'-bis(2-mercaptoethyl)-1,3-propanediamine}, as functional models for [NiFe]hydrogenases. In acidic media (at pH 4-6), the mu-H ligand of the Ni(II)(mu-SR)(2)(mu-H)Ru(II) complexes has H(+) properties, and the complexes catalyse the hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes. A mechanism of the hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes through a low-valent Ni(I)(mu-SR)(2)Ru(I) complex is proposed. In contrast, in neutral-basic media (at pH 7-10), the mu-H ligand of the Ni(II)(mu-SR)(2)(mu-H)Ru(II) complexes acts as H(-), and the complexes catalyse the hydrogenation of carbonyl compounds.

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