Maximizing Electron Exchange in a [Fe3] Cluster.

ABSTRACT: The one-electron reduction of ((tbs)L)Fe?(thf)¹ furnishes [M][((tbs)L)Fe?] ([M]? = [(18-C-6)K(thf)?]? (1, 76%) or [(crypt-222)K]? (2, 54%)). Upon reduction, the ligand (tbs)L?? rearranges around the triiron core to adopt an almost ideal C?-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 (?(M)?) component of the alternating current (ac) magnetic susceptibility data and by the appearance of hyperfine splitting in the zero-field ??Fe 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.

SUBMITTER: Hernandez Sanchez R 

PROVIDER: S-EPMC5567842 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature