392 Mn7 terpy Abhu (IC 2006)

392 Mn7 terpy Abhu (IC 2006) - Inorg. Chem. 2006, 45,...

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[Mn 7 O 5 (OR) 2 (O 2 CPh) 9 (terpy)] (R ) Me, CH 2 Ph) Complexes with a Fused Cubane/Butterfly Core and an S ) 6 Ground-State Spin Abhudaya Mishra, ² Wolfgang Wernsdorfer, Khalil A. Abboud, ² and George Christou* Department of Chemistry, Uni V ersity of Florida, Gaines V ille, Florida 32611-7200, and Laboratoire Louis Ne ´ el-CNRS, BP 166, 25 A V enue des Martyrs, 38042 Grenoble Cedex 9, France Received July 18, 2006 Two new heptanuclear Mn clusters, [Mn 7 O 5 (OMe) 2 (O 2 CPh) 9 (terpy)] ( 1 ) and [Mn 7 O 5 (OCH 2 Ph) 2 (O 2 CPh) 9 (terpy)] ( 2 ), were prepared from the partial alcoholysis of the trinuclear complex [Mn 3 O(O 2 CPh) 6 (py) 2 (H 2 O)] ( 3 ) in the presence of terpy (terpy ) 2,2 :6 ,2 ′′ -terpyridine). Complexes 1 and 2 crystallize in the triclinic P 1 h and the orthorhombic Pbca space groups, respectively. The clusters are both mixed valent, containing three Mn oxidation states: Mn IV , 5Mn III , and Mn II . The Mn ions are held together by nine doubly bridging benzoates, four μ 3 -O 2 - ions, one μ 5 -O 2 - ion, and either two μ -MeO - ( 1 )ortwo μ -PhCH 2 O - ( 2 ) groups. The single terpy chelate in each complex is attached to the Mn II ion. The core topology is novel and very unusual, comprising a cubane and a butterfly unit fused by sharing a Mn III and the μ 5 -O 2 - ion. Solid-state dc and ac magnetic susceptibility studies establish that complexes 1 and 2 both possess an ) 6 ground-state spin. Fits of variable-temperature and -field magnetization data gave ) 6, g ) 1.88, and D ) - 0.21 cm - 1 for 1 and ) 6, ) 1.86, and ) - 0.18 cm - 1 for 2 . Single-crystal magnetization vs dc field scans down to 0.1 K for 2 show only very little hysteresis at 0.1 K. Introduction One of the motivating themes in multinuclear cluster chemistry research is the design of high-nuclearity manga- nese carboxylate clusters that can function as nanoscale magnetic materials. Such species display superparamagnet- like, slow relaxation of the magnetization vector below their blocking temperature ( T B ) and have been termed single- molecule magnets (SMMs). Such molecules function as magnets, exhibiting hysteresis in magnetization versus dc field scans. Since SMMs are, by definition, molecular in nature, they thus represent a molecular, or bottom-up, approach to nanomagnetism. 1 The magnetic behavior of SMMs results from the combination of a large ground spin state ( S ) with a large and negative (Ising or easy-axis) magnetoanisotropy, as measured by the axial zero-field (ZFS) splitting parameter D. This leads to a significant barrier ( U ) to magnetization reversal, its maximum value given by S 2 | D | or ( S 2 - 1/4) | D | for integer and half-integer spin, respec- tively. 1,2 However, in practice, quantum tunneling of the magnetization (QTM) through the barrier via higher lying M S levels of the spin S manifold results in the actual or effective barrier ( U eff ) being less than U .
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392 Mn7 terpy Abhu (IC 2006) - Inorg. Chem. 2006, 45,...

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