Dinuclear Diferrous Complexes of a Bis(tetradentate) Dinucleating Ligand: Influence of the Exogenous Ligands on the Molecular and Electronic Structures

Abstract

AbstractThe ligand susan6−Me (susan6−Me=4,7‐dimethyl‐1,1,10,10‐tetra(6‐methyl‐2‐pyridylmethyl)‐1,4,7,10‐tetraazadecane) allows the synthesis of a peroxo complex that is only a transient species under catalytic conditions with the closely related ligand susan (susan=4,7‐dimethyl‐1,1,10,10‐tetra(2‐pyridylmethyl)‐1,4,7,10‐tetraazadecane). For the synthesis of a peroxo complex analogous to that of susan6−Me we present here the three air‐sensitive complexes [(susan){FeIICl2}2], [(susan){FeII(OTf)2}2], and [(susan){FeII(μ‐OH)2FeII}](ClO4)2 as potential precursors. [(susan){FeII(μ‐OH)2FeII}](ClO4)2 shows weak antiferromagnetic coupling and a g=16 EPR signal. Dissolving [(susan){FeII(OTf)2}2] in CH3CN forms [(susan){FeII(CH3CN)2}2]4+ that shows a spin transition upon cooling as evidenced by UV‐Vis, 1H NMR, and Mössbauer spectroscopies. In the UV‐Vis‐NIR spectra the combination of (i) the energy of the MLCT, (ii) the energy, and (iii) the splitting of the d–d transitions provide insight into the overall electron donation and into the different σ‐donor/π‐donor/π‐acceptor capabilities of the exogenous ligands. These experimental signatures provide insight into the molecular structures in solution e. g. during reactions with O2.