Syntheses, crystal structure, and magnetic properties of Mn12 single-molecule magnets with naphthalenecarboxylate bridges, [Mn12O12(O2CC10H7)16(H2O)4] and their tetraphenylphosphonium salts

The preparation and physical characterization are reported for three Mn-12 single-molecule magnets (SMMs) having naphthalenecarboxylate bridges, [Mn12O12(2-nc)(16)(H2O)(4)] (1, 2-ncH = 2-naphthalenecarboxylic acid), its Ph4P+ salt (2) and [Mn12O12(1-nc)(16)(H2O)(4)] (3, 1-ncH = 1-naphthalenecarboxylic acid). Complex 1 center dot 2CH(2)Cl(2)center dot 4.5H(2)O crystallizes in the monoclinic space group C2/c, with cell dimensions at -160 degrees C of a = 28.524 angstrom, b = 17.819 angstrom, c = 36.058 angstrom, beta = 92.399 degrees, and Z = 4. The X-ray structure analysis of 1 center dot 2CH(2)Cl(2)center dot 4.5H(2)O reveals that each [Mn-12] molecule is connected to the neighboring molecules through eight pi... pi interactions to form a two-dimensional structure within the bc-plane. This is the first SMM that self-assembles two-dimensionally via pi... pi interaction. From Arrhenius plots of the frequency dependence of the temperatures of the X"(M) peaks, the effective energy barriers U-eff for the reversal of the magnetization spin were estimated to be 61 K, 53 K, and 61 K for high-temperature phases of 1-3, respectively, and 31 K and 33 K for the low-temperature (UT) phases of 1 and 3, respectively. The analysis of the reduced magnetization data suggests that the LT phase of I has an S = 9 ground state with g = 1.998 and D = -0.61 K.