Mn₄, Mn₆, and Mn₁₁ Clusters from the Use of Bulky Diphenyl(pyridine-2-yl)methanol

The synthesis, crystal structure, and magnetochemical characterization are reported of three new Mn clusters [Mn₄O₂(O₂CBu^t)₅(dphmp)₃] (1), [Mn₆O₄(OMe)₂(O₂CPh)₄(dphmp)₄] (2), and [Mn₁₁O₇(OMe)₇(O₂CPh)₇(dphmp)₄(MeOH)₂] (3). They were obtained from the use of diphenyl(pyridine-2-yl)methanol (dphmpH), a bulkier version of the 2-(hydroxymethyl)pyridine (hmpH) reagent commonly employed previously in Mn chemistry. The reaction of dphmpH with MnCl₂·4H₂O and NaO₂CBu^t in MeCN/MeOH (30 mL, 5:1 v/v) led to the isolation of tetranuclear complex 1, whereas the analogous reaction with NaO₂CPh gave hexanuclear complex 2. When the 5:1 solvent ratio in the latter reaction was changed to 1:29, the isolated product was now undecanuclear complex 3. Complexes 1−3 all possess rare or unprecedented Mn_x topologies: Complex 1 possesses a [Mn₄(μ₃-O)₂]⁸⁺ (4Mn^III) butterfly core, one edge of which is additionally bridged by an alkoxide arm of a dphmp⁻ chelate; complex 2 possesses a [Mn₆(μ₄-O)₂(μ₃-O)₂(μ₃-OMe)₂]⁸⁺ (6Mn^III) core with a face-sharing double cubane topology; and complex 3 (Mn^II, 10Mn^III) possesses a [Mn₄(μ₄-O)₃(μ₃-OMe)]⁵⁺ cubane unit, attached on one side to a Mn^II atom by a μ₄-O atom and alkoxide groups, and on the other side to a [Mn₅(μ₄-O)(μ₃-O)₃(μ₃-OMe)(μ-OR)₃]³⁺ unit consisting of three face-sharing defective cubanes linked to an additional Mn^III atom by a μ₃-O atom. Solid-state dc and ac magnetic susceptibility measurements on 1−3 establish that they possess S = 0, 3, and 5/2 ground states, respectively. ac susceptibility studies on 2 and 3 reveal weak non-zero frequency-dependent out-of-phase (χ_M′′) signals at temperatures below 3 K, possibly indicative of single-molecule magnets with very small barriers. The combined results demonstrate a ligating difference between bulky dphmp⁻ and hmp⁻, and the resulting usefulness of the former to provide access to a variety of Mn_x molecular species not known with the latter.