[NiFe], [FeFe], and [Fe] hydrogenase models from isomers.

The study of hydrogenase enzymes (Hases) is necessary because of their importance to a future hydrogen energy economy. These enzymes come in three distinct classes: [NiFe] Hases, which have a propensity toward H oxidation; [FeFe] Hases, which have a propensity toward H evolution; and [Fe] Hases, which catalyze H transfer. Modeling these enzymes has so far treated them as different species, which is understandable given the different cores and ligand sets of the natural molecules. Here, we demonstrate, using x-ray analysis and nuclear magnetic resonance, infrared, Mössbauer spectroscopies, and electrochemical measurement, that the catalytic properties of all three enzymes can be mimicked with only three isomers of the same NiFe complex.