The preparation and physical characterization are reported for three Mn12 single-molecule magnets (SMMs) having naphthalenecarboxylate bridges, [Mn12O12(2-nc)16(H2O) 4] (1, 2-ncH = 2-naphthalenecarboxylic acid), its Ph 4P+ salt (2) and [Mn12O12(1-Nc) 16(H2O)4] (3, 1-ncH = 1-naphthalenecarboxylic acid). Complex 1-2CH2Cl2 · 4.5H2O crystallizes in the monoclinic space group C2/c, with cell dimensions at -160 °C of a = 28.524 Å, b = 17.819 Å, c = 36.058 Å, β= 92.399°, and Z = 4. The X-ray structure analysis of 1 · 2CH 2Cl2 · 4.5H2O reveals that each [Mn 12] molecule is connected to the neighboring molecules through eight π⋯π interactions to form a two-dimensional structure within the bc-plane. This is the first SMM that self-assembles two-dimensionally via π⋯π interaction. From Arrhenius plots of the frequency dependence of the temperatures of the χ″M peaks, the effective energy barriers Ueff 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 (LT) phases of 1 and 3, respectively. The analysis of the reduced magnetization data suggests that the LT phase of 1 has an S = 9 ground state with g = 1.998 and D = -0.61 K.
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