Postprint version. Published in Polyhedron, Volume 10, Issue 2, January 1, 1991, pages 203-213. Copyright © 1991 Elsevier. The definitive version is available at http://dx.doi.org/10.1016/S0277-5387(00)81590-9.
NOTE: At the time of publication, the author Richard B. Frankel was not yet affiliated with Cal Poly.
The ground state electronic properties of the mixed-valence clusters Fe7S6 (PEt3)4Cl3 (1), Fe6S6(PEt3)4L2 [L = Cl− (2), Br− (4), I− (5) and PhS− (6)], Fe6Se6 (PEt3)4Cl2 (3) and [Fe6S6(PEt)6]1− (9), have been investigated by magnetic susceptibility, magnetization and Mössbauer spectroscopic measurements. Cluster 1 has a (idealized C3v) monocapped prismane structure and clusters 2–6 and 9 adopt the C2v “basket” configuration based on the [Fe6(μ2-S)(μ3-S)4(μ4-S)]2+,1+ core unit. From magnetic properties, the ground states S = 1/2 (1, 9) and S = 1 (2–5) were established. Unlike the other clusters, 6 did not show a Curie region of susceptibility; its ground state was not directly determined but is probably S = 1. Mössbauer spectra were successfully analysed in terms of a 1 : 1 : 1 iron site population. Isomer shifts and quadrupole splittings were assigned to each site. Magnetically perturbed spectra obtained in applied fields of 60–80 kOe were analysed to give the magnetic hyperfine parameters and magnetic hyperfine fields in clusters 1–5 and 9. The magnetic spectra demonstrate antiferromagnetic spin coupling which affords the indicated ground states.