title: Maximizing Electron Exchange in a [Fe3] Cluster.
abstract: The one-electron reduction of ((tbs)L)Fe₃(thf)¹ furnishes [M][((tbs)L)Fe₃] ([M]⁺ = [(18-C-6)K(thf)₂]⁺ (1, 76%) or [(crypt-222)K]⁺ (2, 54%)). Upon reduction, the ligand (tbs)L⁶⁻ rearranges around the triiron core to adopt an almost ideal C₃-symmetry. Accompanying the ((tbs)L) ligand rearrangement, the THF bound to the neutral starting material is expelled, and the Fe-Fe distances within the trinuclear cluster contract by ∼0.13 Å in 1. Variable-temperature magnetic susceptibility data indicates a well-isolated S = 11/2 spin ground state that persists to room temperature. Slow magnetic relaxation is observed at low temperature as evidenced by the out-of-phase (χ(M)″) component of the alternating current (ac) magnetic susceptibility data and by the appearance of hyperfine splitting in the zero-field ⁵⁷Fe Mössbauer spectra at 4.2 K. Analysis of the ac magnetic susceptibility yields an effective spin reversal barrier (U(eff)) of 22.6(2) cm⁻¹, nearly matching the theoretical barrier of 38.7 cm⁻¹ calculated from the axial zero-field splitting parameter (D = -1.29 cm⁻¹) extracted from the reduced magnetization data. A polycrystalline sample of 1 displays three sextets in the Mössbauer spectrum at 4.2 K (H(ext) = 0) which converge to a single six-line pattern in a frozen 2-MeTHF glass sample, indicating a unique iron environment and thus strong electron delocalization. The spin ground state and ligand rearrangement are discussed within the framework of a fully delocalized cluster exhibiting strong double and direct exchange interactions.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
authors.forename: Raúl
authors.initials: R
authors.lastname: Hernández Sánchez
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
authors.forename: Amymarie K
authors.initials: AK
authors.lastname: Bartholomew
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
authors.forename: Tamara M
authors.initials: TM
authors.lastname: Powers
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Ménard
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
authors.forename: Theodore A
authors.initials: TA
authors.lastname: Betley
mesh_terms: D018360:Crystallography, X-Ray; D004583:Electrons; D058085:Iron Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011789:Quantum Theory; D015204:Spectroscopy, Mossbauer
chemical_list: D058085:Iron Compounds