Synthesis, crystal structure and magnetic properties of novel Mn12 single-molecule magnets with thiophenecarboxylate, [Mn12O12(O2CC4H3S)16(H2O)4], and its tetraphenylphosphonium salt

The preparation and physical characterization are reported for novel Mn-12 single-molecule magnets having thiophenecarboxylate bridges, [Mn12O12(O2CC4H3S)(16)(H2O)(4)] (1), and its PPh4 salt (2). The reaction of the excess amount of 2-thiophenecarboxylic acid (tpcH) and [Mn12O12(OAc)(16)(H2O)(4)] in CH2Cl2 gave black crystals of 1, which could be reduced by PPh4I to give 2. From the crystal structure analysis of 2, it is revealed that there are two five-coordinated Mn ions, one of which is assigned to a Mn-II ion being in the vicinity of the tetraphenylphosphoniurn cation. Both complexes exhibit out-of-phase a.c. magnetic susceptibility (chi(M)'') signals in the 5.0-6.5 K range at 997 Hz a.c. frequency, which indicate that they are single-molecule magnets. From Arrhenius plots of the frequency dependence of the temperature of the chi(M)'' peaks, the effective energy barriers U-eff were estimated to be 69 and 57 K for high-temperature phases of 1 and 2, respectively, and 40 K for the low-temperature phase of 1. The reduced magnetization measurement and its analysis indicate that 2 has S = 19/2 ground state with g = 1.99 and D = -0.61 K. (C) 2003 Elsevier Science Ltd. All rights reserved.