| 19572498 |
Milsmann C, Patra GK, Bill E, Weyhermuller T, DeBeer George S, Wieghardt K: Octahedral monodithiolene complexes of iron: characterization of S,S'-coordinated dithiolate (1-) pi radical monoanions: a spectroscopic and density functional theoretical investigation. Inorg Chem. 2009 Aug 3;48(15):7430-45.
The reaction of cis-[Fe (III)(cyclam) Cl (2)] Cl with 1 equiv of sodium N-diethyldithiocarbamate, toluene-3,4-dithiolate, and maleonitriledithiolate in methanol in the presence of triethylamine afforded the cations [Fe (III)(cyclam)(Et (2) dtc)](2+) (1), [Fe (III)(cyclam)(tdt)](+) (2), and [Fe (III)(cyclam)(mnt)](+) (3), which were isolated as triflate, hexafluorophosphate, and tetrafluoroborate salt, respectively, using sodium triflate, potassium hexafluorophosphate, or sodium tetrafluoroborate as the source for the counteranion. Complexes 1, 2, and 3 possess an S = (1)/(2) ground state (low-spin ferric d (5)). These salts were characterized by X-ray crystallography, UV-vis, Mossbauer, and electron paramagnetic resonance spectroscopies. Cyclic voltammetry revealed that 2 and 3 are reversibly one-electron-reduced, generating neutral 2 (red) and 3 (red), respectively, and one-electron-oxidized, generating dicationic 2 (ox) and 3 (ox), respectively. Fe and S K-edge X-ray absorption spectroscopy (XAS) revealed that 2 (S = (1)/(2)) and 2 (ox) (S = 0) possess a low-spin ferric ion. Complexes 2 and 3 are S,S'-coordinated to a closed-shell dithiolate (2-) ligand, whereas 2 (ox) and 3 (ox) consist of a low-spin ferric ion antiferromagnetically coupled to a dithiolate (1-) pi radical ligand. They are singlet diradicals [Fe (III)(cyclam)(dithiolate (*))](2+). The analysis of the sulfur K pre-edge transitions reveals significant multiplet effects in the spectra of 2 and 2 (ox), which provide rare experimental evidence for a singlet diradical description for 2 (ox). Mossbauer spectroscopy on frozen solutions of 2 (red) clearly show the presence of a high-spin ferrous ion (S = 2). The experimentally established electronic structures of the three members of the electron transfer series [Fe (cyclam)(dithiolate)](2+,+,0) have been verified by broken symmetry density functional theoretical calculations, which have been calibrated against the experiment by calculating XAS and Mossbauer spectra. |
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