The syntheses, structures, and magnetochemical properties are reported for five new Mn clusters: [(Mn3O)-O-III (O2PPh2)(3)(mpko)(3)] (ClO4) (1), [(Mn3O)-O-III (O2PPh2)(3)-(ppko)(3)](ClO4) (2) [(Mn6O2)-O-III(OMe)(4)(O2PPh2)(4)(mpko)(4)]-(ClO4)(2) (3), [(Mn8O6)-O-III (O2CMe)(7)-(O3PPh)(2)(mpko)(3)(H2O)] (4), and [(Mn2MnO)-Mn-III-O-II(mpko)(3)-(H2O)(4)(ClO4)(2)](ClO4) (5), where mpko(-) (or ppko(-)) is the anion of methyl (or phenyl) 2-pyridyl ketone oxime. 1 was obtained by carboxylate substitution on [(Mn3O)-O-III(O2CMe)(3)-(mpko)(3)](ClO4) by treatment with diphenylphosphinic acid (Ph2PO2H). The comproportionation reaction between Mn-(ClO4)(2) and (NBu4MnO4)-Mn-n in the presence of Ph2PO2H and ppkoH in EtOH, or mpkoH in MeOH, led to 2 and 3,respectively. 4 was obtained as was 3, but with phenylphosphonic acid (PhPO3H2) instead of Ph2PO2H. 5 was obtained by aerial oxidation of Mn(ClO4)(2) in the presence of mpkoH. 1 and 2 contain a triangular Mn3 core, 3 comprises the fusion of two Mn-3 units of 1 by MeO- bridges, and 4 has a cagelike structure. 5 is similar to 1 in possessing a triangular core. Variable-temperature, solid-state direct-current (dc) and alternating-current (ac) magnetic data were collected on 1-5: 1 and 2 exhibit ferromagnetic Mn center dot center dot center dot Mn exchange interactions, S = 6 ground states, and are new single-molecule magnets (SMMs). 3-5 possess S = 4, 5/2, and 5/2 ground states, respectively, from dominant antiferromagnetic interactions. Fits of dc magnetization data in the 1.8-10.0 K and 10-70 kG ranges gave D and g values of: 0.29(2) cm(-1) and 1.94(1) for -1, 0.38(2) cm(-1) and 1.99(1) for 2, -0.29(2) cm(-1) and 1.96(1) for 3, -1.26(4) cm(-1) and 1.99(2) for 4, -1.41(4) cm(-1) and 1.98(2) for 5, where D is the axial zero-field splitting parameter.