The reactions of [Mn3O(O2CCCl3)6(H2O)(3)] with 1-phenyl-3-(2-pyridyl)propane-1,3-dione (HL1) and 1-(2-pyridly)-3(p-tolyl)propane-1,3-dione (HL2) in CH2C2 afford the mixed-valence (Mn2Mn2III)-Mn-II tetranuclear complexes [Mn4O(O2CCCl3)(6)(L-1)(2)] (1) and [Mn4O(O2CCCl3)(6)L-2(2)] (2), respectively. Similar reactions employing [Mn3O(O2CPh)(6)(H2O)(PY)(2)] with HL1 and HL2 give the Mn(II)Nn(3)(III) hexanuclear complexes [Mn6O2(O2CPh)(8)(L-1)(3)] (3) and (Mn6O2(O2CPh)(8)L-3(2)] (4), respectively. Complexes 1.2CH(2)Cl(2), 2.2CH(2)Cl(2)center dot H2O, 3.1.5CH(2)Cl(2). Et2O center dot H2O, and 4.2CH(2)Cl(2) crystallize in the triclinic space group P (1) over bar, monoclinic space group P2(1)/c, monoclinic space group P2(1)/c, and monoclinic space group P2(1)/n, respectively. Complexes 1 and 2 consist of a trapped-valence tetranuclear core of [(Mn2Mn2III)-Mn-II(mu(4)-O)](8+), and complexes 3 and 4 represent a new structural type, possessing a [(Mn3Mn3III)-Mn-II(mu(4)-O)(2)](11+) core. The magnetic data indicate that complexes 3 and 4 have a ground-state spin value of S = 7/2 with significant magnetoanisotropy as gauged by the D values of -0.51 cm(-1) and -0.46 cm(-1), respectively, and frequency-dependent out-of-phase signals in alternating current magnetic susceptibility studies indicate their superparamagnetic behavior. In contrast, complexes 1 and 2 are low-spin molecules with an S = 1 ground state. Single-molecule magnetism behavior confirmed for 3 the presence of sweep-rate and temperature-dependent hysteresis loops in single-crystal M versus H studies at temperatures down to 40 mK.