The simple organometallic, (mu-S(2))Fe(2)(CO)(6), serves as a precursor to synthetic analogues of the chemically rudimentary iron-only hydrogenase enzyme active site. The fundamental properties of the (mu-SCH(2)CH(2)CH(2)S)[Fe(CO)(3)](2) compound, including structural mobility and regioselectivity in cyanidecarbon monoxide substitution reactions, relate to the enzyme active site in the form of transition-state structures along reaction paths rather than ground-state structures. Even in the absence of protein-based active-site organization, the ground-state structural model complexes are shown to serve as hydrogenase enzyme reaction models, H(2) uptake and H(2) production, with the input of photo- or electrochemical energy, respectively.