The last twenty years have seen an impressive, perhaps unprecedented collaboration between biochemists, spectroscopists, enzymologists, biophysical, and bioinorganic chemists with regards to the structure and function of nickel-containing hydrogenases.  The protein crytal structure of a {NiFe} H₂ase isolated from the bacterium Desulfovibrio gigas, (Volbeda, A., et al. Nature, 1995, 373, 580; J. Am. Chem. Soc., 1996, 118, 12989) discovered a unique Ni-Fe heterometallic site and the prosthetic group Fe(CN)₂(CO), which is common to several hydrogenases (Happe, R. P. et al. Nature, 1997, 385, 126; Fernandez, et al., J. Am. Chem. Soc., 1997, 119,7181). In the next decade it is hoped that synthetic and mechanistic studies will permit the chemist to determine which parts of the protein are required for catalytic activity, i.e., the production of H₂ from protons and electrons. Our attempts to produce small molecule moldels target the iron-diatomic moiety. A simple organometallic anion, (n⁵ - C₅H₅)Fe(CN)₂(CO)^-, provides a remarkable match for the vibrational spectroscopy and permits exploration of solvent and couterion effects on the IR spectra of the iron-boud carbonyl and cyanide diatomics (Darensbourg, et al., J. Am. Chem. Soc., 1997, 119, 7903).
    We also examine the possible role of the heterobimetallic in redox control of enzyme activity as well as function. The extensive S-Based electrophilic reactivity, hallmark of the bis-mercaptoethyldiazacyclooctane (bme-daco) ligand when bound to nickel, is used in the synthesis of  [N₂S₂]Ni complexes with pendant ZnCl₂, FeX₂, Fe(CO)₄, Fe(CO)_x(CN)_y groups.
The effect of these groups on accessibility and stability of reduced N₂S₂Ni^I, its EPR signature, and its reactivity will be discussed.