Studies of an enneanuclear manganese single-molecule magnet

The reaction of [Mn3O(O2CMe)6(py) 3] with the tripodal ligand H3thme (1,1,1-tris(hydroxymethyl)-ethane) affords the enneanuclear complex [Mn9O7(O 2CCH3)11(thme)(py)3(H 2O)2] 1&middot1MeCN&middot1Et2O. The metallic skeleton of complex 1 comprises a series of 10 edge-sharing triangles that describes part of an idealized icosahedron. Variable temperature direct current (dc) magnetic susceptibility data collected in the 1.8-300 K temperature range and in fields up to 5.5 T were fitted to give a spin ground state of S = 17/2 with an axial zero-field splitting parameter D = -0.29 cm-1. Ac susceptibility studies indicate frequency-dependent out-of-phase signals below 4 K and an effective barrier for the relaxation of the magnetization of U eff = 27 K. Magnetic measurements of single crystals of 1 at low temperature show time- and temperature-dependent hysteresis loops which contain steps at regular intervals of field. Inelastic neutron scattering (INS) studies on complex 1 confirm the S = 17/2 ground state and analysis of the INS transitions within the zero-field split ground state leads to determination of the axial anisotropy, D = -0.249 cm-1, and the crystal field parameter, B40 = 7(4) × 10-6 cm -1. Frequency domain magnetic resonance spectroscopy (FDMRS) determined the same parameters as D = -0.247 cm-1 and B 40 = 4.6 × 10-6 cm-1. DFT calculations are fully consistent with the experimental findings of two Mn(II) and four Mn(III) ions spin up and three Mn(IV) ions spin down resulting in the S = 17/2 spin ground state of the molecule, with D = -0.23 cm-1 and U = 26.2 K. © 2005 American Chemical Society.