FeFe

FeFe is a shorthand notation used in inorganic chemistry and biochemistry to describe a diiron unit, that is, two iron atoms bonded within a larger molecular framework. The term is not a standalone compound but a descriptor for a structural motif common to certain metal complexes and enzymes. In synthetic chemistry, Fe-Fe centers appear in diiron complexes bearing ligands such as carbon monoxide, cyanide, phosphines, or sulfide bridges; these models aim to replicate features of natural active sites and study multi-electron transformations, including hydrogen evolution and uptake.

In biology, the term is frequently encountered in connection with [FeFe]-hydrogenases, a class of enzymes that catalyze reversible conversion between protons and molecular hydrogen. The active site contains a diiron subcluster coordinated by CO and CN ligands and linked to a bridging dithiolate ligand, with the protein environment tuning reactivity. The Fe-Fe core is central to catalytic cycling of proton reduction and hydrogen oxidation.

In materials and catalysis, Fe-Fe centres serve as nodes for multi-electron processes and can support hydride intermediates; their redox flexibility allows access to several oxidation states. Researchers study them for renewable energy applications, including artificial hydrogen-evolving catalysts and CO2 reduction systems.

Because FeFe refers to a motif rather than a specific compound, its precise properties depend on ligands, oxidation state, and the surrounding structure. The context of the discussion clarifies whether the focus is synthetic models, enzymatic activity, or material applications.