Synthesis and characterization of mixed-valent manganese phosphonate cage complexes

The reaction of phenylphosphonic acid (PhPO(3)H(2)) with the mixed-valent basic oxo-centered manganese triangle Mn(3)O(O(2)CCMe(3))(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)(PhPO(3))(14)(O(2)CCMe(3))(12)(py)(6)(H(2)O)(2)] (2), Mn(7)(mu(3)-O)(3)(O(3)PPh)(3)(O(2)CCMe(3))(8)(py)(3)] (3), Mn(9)Na(mu(3)-O)(4)(mu(4)-O)(2)(O(3)PPh)(2)(O(2)CCMe(3))(12)(H(2)O)(2)(H(2)O)(0.67)(Py)(0.33)] (4), and Mn(13)(mu(3)-O)(8)(OMe)(8)(O(3)PPh)(4)(O(2)CCMe(3))(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< or =S > or =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.