Models for the Hydrogenases Put the Focus Where It Should Be—Hydrogen

Not just a pretty face: A new structural model for the [NiFe] hydrogenases (see structure, pale green Ni, dark green Ru, pink S, red H) is also functional: it activates H2 to give a bimetallic hydride and H+. This advance will encourage reinvestigation of the heterolysis of the implied H2 adduct. Questions arise regarding NiII low-spin to high-spin interconversion and reclassification of [FeFe] versus [NiFe] hydrogenase models.