A Scanning Probe Microscopy and Organic Chemistry combination: an extensive characterization of Bis(1-Methyl-2-Benzimidazolyl)Methanone and its Iron Complex

Abstract

Non-innocent ligands are a hot topic in homogeneous catalysis, due to their attractive ability of storing and releasing electrons during the catalytic cycle, conferring noble character to first row transition metals. In this work, a comprehensive overview of the redox active ligand bis(methyl benzimidazolyl)ketone and its Fe complex is presented. The electronic properties of the ligand and the complex, were investigated using cyclic voltammetry (CV). They were found to be quasi-reversible, with a reduction potential of -1.75 V and -1.08 V, respectively. The complex showed a ligand-centred reduction. Electronic behaviours of the ligand and complex were probed also with scanning tunneling spectroscopy (STS), and the positions of their LUMO were identified at 2.07 V and 1.15 V. CV and STS data for the free ligand were compared, showing agreement in the results. The reduction of the ligand was further studied by actually reducing it with Na(s), getting to a doubly and a singly reduced species. These species were both analysed with electron paramagnetic resonance spectroscopy (EPR). The unpaired electron was found to be delocalized over the aromatic system of the ligand. The complex was synthesised on surface via lateral manipulation of single molecules and individual iron atoms. Inelastic electron tunneling spectroscopy (IETS) on the complex, showed signals due to frustrated external vibrations of the molecule. IETS features on the Fe position may be related to Kondo resonance or convolution of substrate-ligand vibrations.