Syntheses, crystal structure, and magnetic properties of Mn₁₂ single-molecule magnets with naphthalenecarboxylate bridges, [Mn ₁₂O₁₂(O₂CC₁₀H₇) ₁₆(H₂O)₄] and their tetraphenylphosphonium salts

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 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 (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.