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

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journal contribution
posted on 2009-10-05, 00:00 authored by Taketo Taguchi, Matthew R. Daniels, Khalil A. Abboud, George Christou
The synthesis, crystal structure, and magnetochemical characterization are reported of three new Mn clusters [Mn4O2(O2CBut)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 NaO2CBut 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 13 all possess rare or unprecedented Mnx topologies: Complex 1 possesses a [Mn43-O)2]8+ (4MnIII) butterfly core, one edge of which is additionally bridged by an alkoxide arm of a dphmp chelate; complex 2 possesses a [Mn64-O)23-O)23-OMe)2]8+ (6MnIII) core with a face-sharing double cubane topology; and complex 3 (MnII, 10MnIII) possesses a [Mn44-O)33-OMe)]5+ cubane unit, attached on one side to a MnII atom by a μ4-O atom and alkoxide groups, and on the other side to a [Mn54-O)(μ3-O)33-OMe)(μ-OR)3]3+ unit consisting of three face-sharing defective cubanes linked to an additional MnIII atom by a μ3-O atom. Solid-state dc and ac magnetic susceptibility measurements on 13 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 (χM′′) 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 Mnx molecular species not known with the latter.

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