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

Abstract

The ligand susan 6À Me (susan 6À Me = 4,7-dimethyl-1,1,10,10-tetra(6methyl-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)-1,4,7,10tetraazadecane). For the synthesis of a peroxo complex analogous to that of susan 6À Me we present here the three airsensitive complexes [(susan){Fe II Cl 2 } 2 ], [(susan){Fe II (OTf) 2 } 2 ], and [(susan){Fe II (μ-OH) 2 Fe II }](ClO 4 ) 2 as potential precursors. [(susan)-{Fe II (μ-OH) 2 Fe II }](ClO 4 ) 2 shows weak antiferromagnetic coupling and a g = 16 EPR signal. Dissolving [(susan){Fe II (OTf) 2 } 2 ] in CH 3 CN forms [(susan){Fe II (CH 3 CN) 2 } 2 ] 4 + that shows a spin transition upon cooling as evidenced by UV-Vis, 1 H 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 O 2 .

Increasing the electron donation in a dinucleating ligand family: molecular and electronic structures in a series of CoIICoII complexes

“…The resulting “diamond-core” in [(susan 6-Me ){Co II (μ-OH) 2 Co II }] 2+ shows alternating short 1.96 and long 2.13 Å Co–O(H) bonds, which was also observed for corresponding diferrous complexes. 26…”

Direct and remote control of electronic structures and redox potentials in μ-oxo diferric complexes

“…The reproducible formation of the mixed complex [(susan OMe ){Fe III (OH)(μ-O)Fe III (OAc)}](ClO 4 ) 2 from an acetone solution without an OAc − source and without the addition of H 2 O 2 is remarkable and we will speculate on a mechanism based on established reactivities of related ligands. The ligands susan 6-Me 20 and susan 40 react with Fe II and NEt 3 to form {Fe II (μ-OH) 2 Fe II } complexes. These react with O 2 to form {Fe III (μ-1,2-peroxo)(μ-oxo)Fe III } species.…”