Electronic Modulation of the SOMO-HOMO Energy Gap in Iron(III) Complexes towards Unimolecular Current Rectification

Amphiphilic five‐coordinate iron(III) complexes with {N2O2Cl} and {N2O3} coordination spheres are studied to elucidate the roles of electronic structure on the mechanisms for current rectification. The presence of an apical chlorido or phenolato ligand plays a crucial role, and the [FeIII{N2O2Cl}] species supports an asymmetric mechanism while its [FeIII{N2O3}] counterpart seems to allow for unimolecular mechanism. The effects of electron‐donating and electron‐withdrawing substituents in the ligand frameworks are also considered. Rectifying the situation: Five‐coordinate iron(III) complexes were investigated to assess the contribution of electronic structure to electron transfer in current rectification by Au|monolayer |Au devices. An [FeIII{N2O2Cl}]‐type species favors an asymmetric mechanism that excludes HOMO participation, whereas [FeIII{N2O3}] with an apical phenolate allows for a unimolecular rectification pathway.