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Reactions of Mn sources with di-2-pyridyl ketone, (2-py)2CO, and phenyl 2-pyridyl ketone oxime, (ph)(2-py)CNOH, give the novel clusters [Mn10(II)Mn4(III)O4(O2CMe)20[(2-py)2C(OH)O]4] 1 and [Mn4(II)Mn4(III)O2(OH)2(O2CPh)10[(ph)(2-py)CNO]4] 2, respectively, which possess low-spin ground states; the observed tetradecanuclearity in 1 is extremely rare in 3d-metal chemistry, while the core of 2 has a unique topology consisting of two linked [Mn2(II)Mn2(III)O(OH)] units.

Single-molecule magnets (SMMs) [1,2] are molecular species that can retain magnetization in the absence of a magnetic field below a blocking temperature. They represent the smallest possible magnetic storage device, which retains information in a single molecule rather than in a magnetic particle or array of particles. Furthermore, such molecules straddle the classical/quantum interface in also displaying quantum tunneling of magnetization and quantum phase interference. The SMM behavior derives from the intrinsic intramolecular properties of a high-spin ground state, and large and negative (easy axis type) magnetoanisotropy. [1,2] Experimentally, a SMM exhibits both a frequency-dependent out-of-phase alternating current (ac) magnetic susceptibility (c'') signal and hysteresis loops in magnetization versus direct current (dc) field studies.[ nÀ (n = 0, 1, 2; x = 3, 4; Mn III 8 Mn IV 4 for n = 0) and their derivatives, [1,2] but there are a number of other examples of SMMs containing manganese (at the oxidation states ii/iii, iii/iv or ii/iii/iv), iron, cobalt, nickel, and vanadium. [1][2][3] Important to the future of the field of SMMs is the development of new synthetic schemes that can yield molecules with a large spin and/or anisotropy. Herein we report access to the first members of a new class of manganese-based SMMs consisting exclusively of Mn III ions with T B (T B = blocking temperature) greater than 2 K.

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An analysis of the measured magnetic susceptibility of the recently synthesized magnetic molecule ͕Fe 8 ͖-cubane ͓͑Fe 8 III O 4 ͑sao͒ 8 ͑py͒ 4 ͔͒ leads to a detailed proposal based on an isotropic Heisenberg model for the interactions between the eight Fe III ions. In the theoretical model, the magnetic ions are situated on the vertices of a cube with one exchange constant linking nearest neighbors and a second exchange constant ͑appearing as a single diagonal across each of the six faces of the cube͒ linking four of the eight ions on alternate sites. Excellent agreement between the experimental and theoretical susceptibility data is achieved, thereby providing estimates for the numerical values of the two exchange constants. Independent tests of the theoretical model are proposed in terms of inelastic neutron scattering and high-field magnetic susceptibility measurements at low temperatures that would probe the predicted low-lying magnetic energy levels of the system.