Treatment of [Mn12O12(O(2)CMe)(16)(H2O)(4)] (1) with an excess of EtCO(2)H in toluene leads to high yield (similar to 70%) conversion to [Mn12O12(O(2)CEt)(16)(H2O)(3)] (3) Complex 3.4H(2)O crystallizes in the triclinic space group P1, which at -165 degrees C has a = 13.851(3) Angstrom, b = 23.431(5) Angstrom, c = 13.663(3) Angstrom, alpha = 103.76(1)degrees, beta = 111.46(1)degrees, gamma = 78.13(1)degrees, and Z = 2. The structure was refined with 8470 observed [F > 3.0 sigma(F)] reflections to give R = 6.07 and R(W) = 6.21%. The complex consists of a central [(Mn4O4)-O-IV](8+) cubane held within a nonplanar ring of eight Mn-III atoms by eight mu(3)-O2- ions. One of the Mn-III ions is five coordinate. NMR (H-1,F-19) studies on [Mn12O12(O(2)CR)(16)(H2O)(4)] (R = Me,Et, and substituted Ph) show that the dodecanuclear species retain their structural integrity upon dissolution in CD3CN. The spectra show four carboxylate resonances, consistent with effective D-2 minimal symmetry in solution. Electrochemical studies on 1-3 and a series of related species show a quasireversible reduction in the 0.00 to 0.47 V range, and a quasireversible oxidation in the 0.70 to 1.07 V range, together with additional mostly irreversible oxidation and reduction processes. Reduction of complex 3 with PP4I in CH2Cl2 leads to isolation of (PPh(4))[Mn12O12(O(2)CEt)(16)(H2O)(4)] (4) in similar to 70% yield. Complex 4 crystallizes in monoclinic space group P2(1)/c with the following cell dimensions at -168 degrees C : a 13.046(4), b = 28.223(9), c = 27.162(8) Angstrom, beta = 96.32(1)degrees, Z = 4, and V = 9940.45 Angstrom(3). The structure was refined using 9871 unique reflections with I > 3 sigma(I) to give R = 6.51 and R(W) = 6.65%, respectively. The structure shows that the added electron is localized on an outer (originally Mn-III) ion rather than an inner (cubane) Mn-IV ion, producing a trapped-valence (MnMn7Mn4IV)-Mn-II-Mn-III anion.