Synthesis and characterization of four consecutive members of the five-member [Fe6S8(PEt(3))(6)](n+) (n=0-4) cluster electron transfer series

The clusters [Fe6S8(PEt(3))(6)](+,2+) have been shown by other investigators to be formed by the reaction of [Fe(OH2)(6)](2+) and H2S, to contain face-capped octahedral Fe6S8 cores, and to be components of the five-membered electron transfer series [Fe6S8(PEt(3))(6)](n+) (n = 0-4) established electrochemically. We have prepared two additional series members. Reaction of [Fe6S8(PEt(3))(6)](2+) with iodine in dichloromethane affords [Fe6S8(PEt(3))(6)](3+), isolated as the perchlorate salt (48%). Reduction of [Fe6S8(PEt(3))(6)](2+) With Na(Ph(2)CO) in acetonitrile/THF produces the neutral cluster [Fe6S8(PEt(3))(6)] (65%). The structures of the four clusters with n = 0, If, 2+, 3+ were determined at 223 K. The compounds [Fe6S8(PEt(3))(6)](ClO4)(3), [Fe6S8(PEt(3))(6)] crystallize in trigonal space group R(3) over barc$ with a = 21.691(4), 16.951(4) Angstrom, c = 23.235(6), 19.369(4) Angstrom, and Z = 6, 3. The compounds [Fe6S8(PEt(3))(6)](BF4)(2), [Fe6S8(PEt(3))(6)](BF4). 2MeCN were obtained in monoclinic space groups P2(1)/c, C2/c with a = 11.673(3), 16.371(4) Angstrom, b = 20.810(5), 16.796(4) Angstrom, c = 12.438(4), 23.617(7) Angstrom, beta = 96.10(2), 97.98(2)degrees, and Z = 2, 4. [Fe6S8(PEt(3))(6)](BPh(4))(2) occurred in trigonal space group P (1) over bar with a = 11.792(4) Angstrom, b = 14.350(5) Angstrom, c = 15.536(6) Angstrom, alpha = 115.33(3)degrees, beta = 90.34(3)degrees, gamma = 104.49(3)degrees, and Z = 1. Changes in metric features across the series are slight but indicate increasing population of antibonding Fe6S8 core orbitals upon reduction. Zero-field Mossbauer spectra are consistent with this result, isomer shifts increasing by ca. 0.05 mm/s for each electron added, and indicate a delocalized electronic structure. Magnetic susceptibility measurements together with previously reported results established the ground states S = 3/2 (3+), 3 (2+), 7/2 (1+), 3 (0) The clusters [Fe6S8(PEt(3))(6)](n+) possess the structural and electronic features requisite to multisequential electron transfer reactions. This work provides the first example of a cluster type isolated over four consecutive oxidation states. Note is also made of the significance of the [Fe6S8(PEt(3))(6)](n+) cluster type in the development of iron-sulfur-phosphine cluster chemistry.