The one-electron reduction of (L-tbs)Fe-3(thf)(1) furnishes [M][(L-tbs)Fe-3] ([M](+) = [(18-C-6)K(thf)(2)](+) (1, 76%) or [(crypt-222)K](+) (2, 54%)). Upon reduction, the ligand L-tbs(6-) rearranges around the triiron core to adopt an almost ideal C-3-symmetry. Accompanying the (L-tbs) ligand rearrangement, the THE bound to the neutral starting material is expelled, and the Fe-Fe distances within the trinuclear cluster contract by similar to 0.13 angstrom 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 (chi(M)'') component of the alternating current (ac) magnetic susceptibility data and by the appearance of hyperfine splitting in the zero-field Fe-57 Mossbauer 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 Mossbauer 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.