Synthesis and Characterization of Mixed-Valent Manganese Phosphonate Cage Complexes

reaction of phenylphosphonic acid (PhPO3H2) with the mixed-valent basic oxo-centered manganese triangle [Mn3O(O2CCMe3)(6)(py)(3)] (1; where py=pyridine) in the presence of a suitable base gives four different manganese clusters depending on the identity of the base. The syntheses and structural characterization of [Mn-18(mu(3)-O)(8)(PhPO3)(14)(O2CCMe3)(12)(py)(6)(H2O)(2)] (2), [Mn-7(mu(3)-O)(3)(O3PPh)(3)(O2CCMe3)(8)(py)(3)] (3), [Mn9Na(mu(3)-O)(4)(mu(4)-O)(2)- (O3PPh)(2)(O2CCMe3)(12)(H2O)(2)(H2O)(0.67)(Py)(0.33)] (4), and [Mn-13(mu(3)-O)(8)(OMe)(8)(O3PPh)(4)(O2CCMe3)(10)] (5) are described. Complexes 4 and 5 are homovalent Mn-III cages, while 2 and 3 contain divalent, trivalent, and/or tetravalent ions. All the manganese centers are valence-localized, the octahedral Mn-III sites being recognizable by marked Jahn-Teller distortions. The magnetic properties of compounds 2-5 have been investigated in the polycrystalline state by magnetic susceptibility and high-field magnetization measurements, which reveal that spin ground states vary from 0 <= S >= 8. AC susceptibility measurements performed on 4 and 5, in the 1.6-10.0 K ranges show the presence of out of AC susceptibility signal (chi(M)") for 4, and an effective energy barrier (U-eff) for the re-orientation of the magnetization is found to be 17 K, but for 5, the chi(M)" maximum is found to be below 1.5 K.