Abstract
The ability of a benzoquinonoid bridging ligand to mediate double-exchange coupling in a mixed-valence Fe2 complex is demonstrated. Metalation of the bridging ligand 2,5-di(2,6-dimethylanilino)-3,6-dibromo-1,4-benzoquinone (LH2) with FeII in the presence of the capping ligand tris((6-methyl-2-pyridyl)methyl)amine (Me3TPyA) affords the dinuclear complex [(Me3TPyA)2FeII2(L)]2+. The dc magnetic measurements, in conjunction with X-ray diffraction and Mössbauer spectroscopy, reveal the presence of weak ferromagnetic superexchange coupling between FeII centers through the diamagnetic bridging ligand to give an S = 4 ground state. The ac magnetic susceptibility measurements, collected in a small dc field, show this complex to behave as a single-molecule magnet with a relaxation barrier of Ueff = 14(1) cm-1. The slow magnetic relaxation in the FeII2 complex can be switched off through one-electron oxidation to the mixed-valence congener [(Me3TPyA)2Fe2(L)]3+, where X-ray diffraction and Mössbauer spectroscopy indicate a metal-centered oxidation. The dc magnetic measurements show an S = 9/2 ground state for the mixed-valence complex, stemming from strong ferromagnetic exchange coupling that is best described considering electron hopping through a double-exchange coupling mechanism, with a double-exchange parameter of B = 69(4) cm-1. In accordance with double-exchange, an intense feature is observed in the near-infrared region and is assigned as an intervalence charge-transfer band. The rate of intervalence electron hopping is comparable to that of the Mössbauer time scale, such that variable-temperature Mössbauer spectra reveal a thermally activated transition from a valence-trapped to detrapped state and provide an activation energy for electron hopping of 63(8) cm-1. These results demonstrate the ability of quinonoid ligands to mediate electron hopping between high-spin metal centers, by providing the first example of an Fe complex that exhibits double-exchange through an organic bridging ligand and the largest metal-metal separation yet observed in any metal complex with double-exchange coupling.
Original language | English (US) |
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Pages (from-to) | 12617-12626 |
Number of pages | 10 |
Journal | Journal of the American Chemical Society |
Volume | 137 |
Issue number | 39 |
DOIs | |
State | Published - Oct 7 2015 |
ASJC Scopus subject areas
- Catalysis
- Chemistry(all)
- Biochemistry
- Colloid and Surface Chemistry
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CCDC 1432902: Experimental Crystal Structure Determination
Gaudette, A. I. (Creator), Jeon, I. (Creator), Anderson, J. S. (Creator), Grandjean, F. (Creator), Long, G. J. (Creator) & Harris, T. D. (Creator), Cambridge Crystallographic Data Centre, 2015
DOI: 10.5517/cc1k31nc, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/cc1k31nc&sid=DataCite
Dataset
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CCDC 1432903: Experimental Crystal Structure Determination
Gaudette, A. I. (Creator), Jeon, I. (Creator), Anderson, J. S. (Creator), Grandjean, F. (Creator), Long, G. J. (Creator) & Harris, T. D. (Creator), Cambridge Crystallographic Data Centre, 2015
DOI: 10.5517/cc1k31pd, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/cc1k31pd&sid=DataCite
Dataset