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Single-Molecule Magnetism Properties of the First Strontium-Manganese Cluster [SrMn14O11(OMe)3(O2CPh)18(MeCN)2]

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journal contribution
posted on 17.03.2008, 00:00 by Abhudaya Mishra, Yulia Pushkar, Junko Yano, Vittal K. Yachandra, Wolfgang Wernsdorfer, Khalil A. Abboud, George Christou
The preparation and properties of the first strontium-manganese molecular complex are described. The reaction of (NBun4)[Mn4O2(O2CPh)9(H2O)] (4MnIII) with Sr(ClO4)2 in MeCN/MeOH led to the isolation of [SrMn14O11(OMe)3(O2CPh)18(MeCN)2] (1; 13MnIII, MnII). The structure of 1 consists of two [Mn4O3(OMe)] cubane units attached to a central, near-planar, trinuclear [Mn3O4] unit, to which are also attached a Mn and a Sr above the plane and a [Mn2O(OMe)] rhomb below the plane. Peripheral ligation is provided by 18 bridging benzoate and two terminal MeCN groups. Variable-temperature and -field dc magnetization (M) data were collected in the 1.8–10 K and 0.1–4.0 T ranges and fit by matrix diagonalization methods to give S = 9/2, D = −0.50(5) cm−1, and g = 1.88(10), where S is the ground-state spin and D is the axial zero-field splitting parameter. Magnetization versus dc field sweeps at various temperatures and scan rates exhibited hysteresis loops, confirming 1 to be a new single-molecule magnet. Because complex 1 is the initial molecular example of intimately associated Mn and Sr atoms, Sr EXAFS studies have been performed for the first time on a synthetic Sr-containing molecule. This has also allowed comparisons with the EXAFS data on the Sr-substituted water oxidizing complex (WOC) of Photosystem II (PS II), which contains a SrMn4 complex.