[((H)L)2Fe6(NCMe)m]n+ (m = 0, 2, 4, 6; n = -1, 0, 1, 2, 3, 4, 6): an electron-transfer series featuring octahedral Fe6 clusters supported by a hexaamide ligand platform.

Using a trinucleating hexaamide ligand platform, the all-ferrous hexanuclear cluster ((H)L)(2)Fe(6) (1) is obtained from reaction of 3 equiv of Fe(2)(Mes)(4) (Mes = 2,4,6-Me(3)C(6)H(2)) with 2 equiv of the ligand ((H)L)H(6). Compound 1 was characterized by X-ray diffraction analysis, (57)Fe Mössbauer, SQUID magnetometry, mass spectrometry, and combustion analysis, providing evidence for an S=6 ground state and delocalized electronic structure. The cyclic voltammogram of ((H)L)(2)Fe(6) in acetonitrile reveals a rich redox chemistry, featuring five fully reversible redox events that span six oxidation states (((H)L)(2)Fe(6), where n=-1→4) within a 1.3 V potential range. Accordingly, each of these species is readily accessed chemically to provide the electron-transfer series [((H)L)(2)Fe(6)(NCMe)(m)]PF(6) (m=0, n=-1 (2); m=2, n=1 (3); m=4, n=2 (4); m=6, n=3 (5); m=6, n=4 (6)). Compounds 2-6 were isolated and characterized by X-ray diffraction, (57)Fe Mössbauer and multinuclear NMR spectroscopy, and combustion analysis. Two-electron oxidation of the tetracationic cluster in 6 by 2 equiv of NO generates the thermally unstable hexacationic cluster ((H)L)(2)Fe(6)(NCMe)(m), which is characterized by NMR and (57)Fe Mössbauer spectroscopy. Importantly, several stepwise systematic metrical changes accompany oxidation state changes to the [Fe(6)] core, namely trans ligation of solvent molecules and variation in Mössbauer spectra, spin ground state, and intracluster Fe-Fe separation. The observed metrical changes are rationalized by considering a qualitative, delocalized molecular orbital description, which provides a set of frontier orbitals populated by Fe 3d electrons.