The syntheses, crystal structures, and magnetochemical characterization are reported for two new Mn clusters, [Mn7O3(OH)(3)(O2CBut)(7)(dmhmp)(4)] (1) and [Mn12O7(OH)(OMe)(2)(O2CPh)(12)(dmhmp)(4)(H2O)] (2). They were obtained from the use of 2-(pyridine-2-yl)propan-2-ol (dmhmpH), a more bulky version of the 2-(hydroxymethyl)pyridine (hmpH) reagent commonly employed previously in Mn chemistry. The reaction of dmhmpH with MnCl2 center dot 4H(2)O and NaO2CBut in MeCN/MeOH led to the heptanuclear complex 1, whereas the analogous reaction with Mn(O2CPh)(2) gave dodecanuclear complex 2. Complexes 1 and 2 are both mixed-valent and are of unprecedented structural types, Complex 1 (Mn-II, 6Mn(III)) can be described as the fusion of butterfly-like [Mn-4(mu(3)-O)(2)] and tetrahedral [Mn-4(mu(4)-O)] units by the sharing of a common Mn atom. Complex 2 (3Mn(II), 9Mn(III)) possesses a central [Mn4O6] face-sharing incomplete dicubane, on either side of which is a tetrahedral [Mn-4(mu(4)-O)] unit attached to the oxide ions of the former. Solid-state dc and ac magnetic susceptibility measurements on 1 and 2 establish that they possess unusual S = 7/2 and 13/2 ground states, respectively. The ac susceptibility studies on 2 revealed nonzero frequency-dependent out-of-phase (chi(M)'') signals at temperatures below 3 K, indicating a single-molecule magnet (SMM). Magnetization versus applied dc field sweeps on single crystals of 2 center dot 3CH(2)Cl(2) down to 0.04 K exhibited hysteresis, thus confirming complex 2 to be a new half-integer SMM.