Combination of Scanning Probe Microscopy and Coordination Chemistry: Structural and Electronic Study of Bis(methylbenzimidazolyl)ketone and Its Iron Complex

Here, we report the bulk synthesis of [Fe^II(BMBIK)Cl₂] bearing the redox noninnocent bis(methylbenzimidazolyl)ketone (BMBIK) ligand and the synthesis of the similar complex [Fe^I(BMBIK)]⁺ on a Au(111) surface using lateral manipulation at the atomic level. Cyclic voltammetry and scanning tunneling spectroscopy are shown to be useful techniques to compare the coordination compound in solution with the one on the surface. The total charge, as well as the oxidation and spin state of [Fe^I(BMBIK)]⁺, are investigated by comparison of the shape of the lowest unoccupied molecular orbital (LUMO), visualized by tunneling through the LUMO, with theoretical models. The similar reduction potentials found for the solution and surface compounds indicate that the major effect of lowering the LUMO upon coordination of BMBIK to the iron center is conserved on the surface. The synthesis and analysis of [Fe^I(BMBIK)]⁺ using scanning tunneling microscopy, scanning tunneling spectroscopy, and atomic force microscopy are the first steps toward mechanistic studies of homogeneous catalysts with redox noninnocent ligands at the single molecule level.