Single-molecule magnets:: A family of MnIII/CeIV complexes with a [Mn8CeO8]12+ core

Four heterometallic, enneanuclear Mn8Ce clusters [Mn8CeO8(O2CMe)(12)(H2O)(4)] (4), [Mn8CeO8(O2CMe)(12)(PY)(4)] (5), [Mn8CeO8(O2CPh)(12)(MeCN)(4)] [Mn8CeO8(O2CPh)(12)(dioxane)(4)] (6), and [Mn8CeO8(O2CCHPh2)(12)(H2O)(4)] (7) have been prepared by various methods. Their cores are essentially isostructural and comprise a nonplanar, saddlelike [(Mn8O8)-O-III](8+) loop containing a central Ce-IV ion attached to the eight mu(3)-O2- ions. Peripheral ligation around the [Mn8CeO8](12+) core is provided by eight mu- and four mu(3)-O2CR- groups. Terminal ligation on four Mn-III atoms is provided by H2O in 4 and 7, pyridine in 5, and MeCN/dioxane in 6. Solid-state magnetic susceptibility studies, fits of dc magnetization vs field and temperature data, and in-phase ac susceptibility studies in a zero dc field have established that complexes 4, 5, and 7 possess S = 16, S = 4 or 5, and = 6 1 spin ground states, respectively, but in all cases there are very low-lying excited states. The large variation in the ground-state spins for this isostructural family is rationalized as due to a combination of weak exchange interactions between the constituent Mn-III atoms, and the presence of both nearest-neighbor and next-nearest-interactions of comparable magnitudes. Magnetization vs applied dc field sweeps on single crystals of 4 center dot 4H(2)O and 7 center dot 4H(2)O center dot 3MeCN center dot 2CH(2)Cl(2) down to 0.04 K have established that these two complexes are new single-molecule magnets (SMMs). The former also shows an exchange-bias, a perturbation of its single-molecule properties from very weak intermolecular interactions mediated by hydrogen-bonding interactions with lattice-water molecules of crystallization.