The anodic one-electron oxidation of three members of the half-sandwich family of piano-stool compounds MnCp gamma(CO)(3), where Cp-gamma is a generic cyclopentadienyl ligand, has been studied in a CH2Cl2/ [NBu4][TFAB] electrolyte (TFAB = [B(C6F5)(4)](-)). The long-sought 17 e(-) radical cation of the parent complex MnCP(CO)3 (cymantrene, 1, E-1/2 = 0.92 V vs ferrocene) has been shown to be persistent in solutions that use weakly coordinating anions in place of more nucleophilic traditional electrolyte anions. Spectroscopically characterized for the first time, 1(+) was shown to absorb in the visible (530 nm), near-IR (2066 nm), and IR (2118, 1934 cm(-1)) regions. It was ESR-active at low temperatures (g(parallel to) = 2.213, g(perpendicular to) = 2.079, A(parallel to) (Mn) = 79.2 G, A(perpendicular to) (Mn) = 50 G) and NMR active at room temperature (delta = 22.4 vs TMS). The radical cations of the Cp-functionalized analogues, Mn(eta(5)-C5H4NH2)(CO)(3), 2, E-1/2 = 0.62 V, and MnCP*(CO)(3) (CP*=eta(5)-C5Me5, 3), E-1/2 = 0.64 V, were generated electrochemically as well by the chemical oxidant [ReCP(CO)3](+). The structures of 2(+) and 3(+) were determined by X-ray crystallographic studies of their TFAB salts. Compared to the structures of the corresponding neutral compounds, the catibris showed elongated Mn-C(O) bonds and shortened C-O bonds, displaying the effect of diminished metal-to-CO backbonding. Thebond-length changes in the Mn(CO)(3) moiety were much larger in 3(+) (avg changes, Mn-C(O) = + 0. 142 angstrom, C-O = -0.063 angstrom) than in 2(+) (avg changes, Mn-C(O) = + 0.006 A, C-0 = -0.003 A). Although there were only minor changes in the metal-to-center ring distances upon oxidation of either 2 or 3, there was decidedly less bending of the C(N) atom out of the cyclopentadienyl plane in 2(+) compared to 2. The optical, vibrational, and magnetic resonance spectra of radicals 2(+) and 3(+) were also observed. The spectral data argue for the SOMOs of the 17-electron species being largely located on the Mn(CO)3 moiety, having 40-50% Mn d-orbital character, with the ground states of the radicals, most likely 2A '', lying close in energy (within about 6000 cm(-1)) to excited states that are responsible for their rapid electronic relaxations. The cymantrenyl moiety is proposed as an anodic redox tag (or label) having physical and chemical properties that are significantly different from those of its ferrocenyl analogue.