Currently, there are only a handful of synthetic S = 2 oxoiron (IV) complexes. These serve as models for the high-spin (S = 2) oxoiron(IV) species that have been postulated, and confirmed in several cases, as key intermediates in the catalytic cycles of a variety of nonheme oxygen activating enzymes. The trigonal bipyramidal complex [Fe-IV(O)(TMG(3)tren)](2+) (1) was both the first S = 2 oxoiron(IV) model complex to be generated in high yield and the first to be crystallographically characterized. In this study, we demonstrate that the TMG(3)tren ligand is also capable of supporting, a tricationic cyanoiron(IV) unit, [Fe-IV(CN)(TMG(3)tren)](3+) (4). This complex was generated by electrolytic oxidation of the high-spin (S = 2) iron(II) complex [Fe-II(CN)(TMG(3)tren)](+) (2), via the S = 5/2 complex [Fe-III(CN)(TMG(3)tren)](2+) (3), the progress of which was conveniently monitored by using UV-vis spectroscopy to follow the growth of bathochromically shifting ligand-to-metal charge transfer (LMCT) bands. A combination of X-ray absorption spectroscopy (XAS), Mossbauer and NMR spectroscopies was used to establish that 4 has a S = 0 iron(IV) center. Consistent with its diamagnetic iron(IV) ground state, extended X-ray absorption fine structure (EXAFS) analysis of 4 indicated a significant contraction of the iron-donor atom bond lengths, relative to those of the crystallographically characterized complexes 2 and 3. Notably, 4 has an Fe-IV/III reduction potential of similar to 1.4 V vs Fc(+/o), the highest value yet observed for a monoiron complex. The relatively high stability of 4 (t(1/2) in CD3CN solution containing 0.1 M KPF6 at 25 degrees C approximate to 15 min), as reflected by its high-yield accumulation via slow bulk electrolysis and amenability to C-13 NMR at -40 degrees C, highlights the ability of the sterically protecting, highly basic peralkylguanidyl donors of the TMG(3)tren ligand to support highly charged high-valent complexes.