Full title: Synthesis, structural characterization, and electronic structures of the "mixed" terminal ligand cubanes [Fe4S4Cl2(XC6H5) 2]2- (X = S, O) and [Fe4S4(SC6H5)2(OC 6H4-p-CH3)2]2-. The first examples of [Fe4S4]2+ cores with a noncompressed D2d idealized geometry. Mixed terminal ligand iron-sulfur clusters of the type (Ph4P)2[Fe4S4(L) 2(L′)2] (L = SPh, L′ = Cl, OPh, Br; L = OPh, L′ = Cl) have been synthesized in good yields by the reaction of [Fe4S4X4]2- (X = Cl, Br) with 2 equiv of KSPh or NaOPh and by the reaction of [Fe4S4(SPh)2Cl2]2- with 2 equiv of NaOPh, respectively. The crystal structures of (Ph4P)2[Fe4S4(XPh) 2Cl2] (I, X = S; II, X = O) and (Ph4P)2[Fe4S4(SPh) 2(OPh-P-CH3)2] (III) are described in detail. Crystalline salts of I and II show symmetry consistent with the orthorhombic space group Pbcn with cell a = 13.082 (1) Å, b = 21.182 (4) Å, and c = 21.376 (4) Å and a = 13.060 (3) Å, b = 20.891 (5) Å, and c = 21.423 (7) Å, respectively. Salt III belongs to the noncentrosymmetric orthorhombic space group P21212 with cell constants a = 24.595 (7) Å, b = 12.588 (3) Å, and c = 10.877 (3) Å. In all structures all non-hydrogen atoms were refined anisotropically and hydrogen atoms were included in the structure factor calculation but not refined. Refinement by full-matrix least squares of 334 parameters on 2203 data for I, 334 parameters on 2149 data for II, and 397 parameters on 3231 data for III gave final R values of 0.061, 0.061, and 0.066, respectively. The anions in I and II are located on the crystallographically imposed twofold axis. The mean Fe-S* bond lengths in I and II are 2.278 (5) and 2.285 (5) Å, respectively. The Fe4S4* cores in I and II represent the first examples of such cores without an overall compressed D2d geometry. The anion in III also is located on a crystallographic twofold axis. The Fe4S4* unit can be described as slightly compressed along an axis that is perpendicular to the crystallographic twofold. The terminal Fe-SPh bond lengths in I and III are 2.261 (3) and 2.289 (3) Å, respectively. The Fe-OAr bond lengths in II and III are found at 2.057 (9) and 1.996 (9) Å, respectively. The electronic and 1H NMR spectra and solution magnetic studies are reported. Zero field Mössbauer spectra of I, II, and III show one doublet that consists of two poorly resolved quadrupole doublets with very similar isomer shift values. A fitting procedure using two Lorentzian lines with the restriction of equal areas yields (at 77 K) δ1 = 0.46, ΔEQ1 = 0.64, δ2 = 0.48, and ΔEQ2 = 0.96 mm/s for I, δ1 = 0.49, ΔEQ1 = 0.78, δ2 = 0.50, and ΔEQ2 = 1.09 mm/s for II, and δ1 = 0.48, ΔEQ1 = 0.91, δ2 = 0.47, and ΔEQ2 = 1.19 mm/s for III. Cyclic voltammetric studies in CH3CN and DMF show that I and III reduce reversibly by one electron while II shows quasi-reversible reduction.
|Number of pages||12|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - 1984|
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