The syntheses, structures, and magnetic properties are reported of [Mn12O12(O(2)CPe(t))(16)(MeOH)(4)] (4), [Mn6O2-(O2CH2)(O(2)CPe(t))(11) (HO(2)CPe(t))(2)(O2CMe)] (5), [Mn9O6(OH)(CO3)(O(2)CPe(t))(12)(H2O)(2)] (6), and [Mn4O2(O(2)CPe(t))(6)(bpy)(2)] (7, bpy = 2,2'-bipyridine), where Pe(t) = tert-pentyl (Pe(t)CO(2)H = 2,2-dimethylbutyric acid). These complexes were all prepared from reactions of [Mn12O12(O(2)CPe(t))(16)(H2O)(4)] (3) in CH2Cl2. Complex 4 center dot 2MeCN crystallizes in the triclinic space group P (1) over bar and contains a central [(Mn4O4)-O-IV] cubane core that is surrounded by a nonplanar ring of eight alternating Will and eight mu(3)-O2- ions. This is only the third Mn-12 complex in which the four bound water molecules have been replaced by other ligands, in this case MeOH. Complex 5 center dot(1)/2CH2Cl2 crystallizes in the monoclinic space group P2(1)/c and contains two [Mn-3(mu(3)-O)](7+) units linked at two of their apexes by two Pe(t)CO(2)(-) ligands and one mu(4)-CH2O22- bridge, The complex is a new structural type in Mn chemistry, and also contains only the third example of a gem-diolate unit bridging four metal ions. Complex 6 center dot H2O center dot Pe(t)CO(2)H crystallizes in the orthorhombic space group Cmc2(1) and possesses a [Mn-9(III)(mu(3)-O)(6)(mu-OH)(mu(3)-CO3)](12+) core. The molecule contains a mu(3)-CO32- ion, the first example in a discrete Mn complex. Complex 7 center dot 2H(2)O crystallizes in the monoclinic space group P2(1)/c and contains a known[(Mn2Mn2II)-Mn-III(mu(3)-O)(2)](6+) core that can be considered as two edge-sharing, triangular [Mn3O] units. Additionally, the synthesis and magnetic properties of a new enneanuclear cluster of formula [Mn9O7(O2CCH2-Bu-t (13)(THF)(2)] (8, THF = tetrahydrofuran) are reported. The molecule was obtained by the reaction of [Mn12O12(O2-CCH2But)(13)(H2O)(4)] (2) with THF. Complexes 2 and 4 display quasireversible redox couples when examined by cyclic voltammetry in CH2Cl2; oxidations are observed at -0.07 V (2) and -0.21 V (4) vs ferrocene, The magnetic properties of complexes 4-8 have been studied by direct current (DC) and alternating current (AC) magnetic susceptibility techniques. The ground-state spin of 4 was established by magnetization measurements in the 1.80-4.00 K and 0.5-7 T ranges. Fitting of the reduced magnetization data by full matrix diagonalization, incorporating a full powder average and including only axial anisotropy, gave S = 10, g = 2.0(1), and D = -0.39(10) cm(-1). The complex exhibits two frequency-dependent out-of-pase AID susceptibility signals (chi(M)") indicative of slow magnetization relaxation. An Arrhenius plot obtained from chi(M)" vs T data gave an effective energy barrier to relaxation (U-eff) of 62 and 35 K for the slower and faster relaxing species, respectively. These studies suggest that complex 4 is a single-molecule magnet (M). DC susceptibility studies on complexes 5-8 display overall antiferromagnetic behavior and indicate ground-state spin values of S <= 2. AC susceptibility studies at < 10 K confirm these small values and indicate the population of low-lying excited states even at these low temperatures. This supports the small ground-state spin values to be due to spin frustration effects.