A Mn₄ single-molecule magnet with the defective-dicubane structure from the use of pyrenecarboxylic acid

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• 作者：Tu N. Nguyen ; Khalil A. Abboud ; George Christou
• 关键词：Manganese ; Crystal structure ; Single-molecule magnet ; 蟺&ndash ; 蟺 Stacking
• 刊名：Polyhedron
• 出版年：13 December, 2013
• 年：2013
• 卷：66
• 期：Complete
• 页码：171-178
• 全文大小：1520 K

文摘

The reaction between Mn(pc)₂路4H₂O (pcH is 1-pyrenecarboxylic acid), N-methyldiethanolamine (mdaH₂), and NEt₃ in a 2:2:3 molar ratio in CH₂Cl₂ or CHCl₃ gives the tetranuclear complex [Mn₄(pc)₄(mda)₂(mdaH)₂], isolated as the 路2CH₂Cl₂ (3) and 路2CHCl₃ (4) solvates, respectively. Only crystals of 4 were of sufficient quality for single-crystal X-ray crystallography. Complex 4 possesses a [Mn^II₂Mn^III₂] core with the Mn ions arranged in a planar rhombus that can be described as two Mn₃ triangles fused at one edge. Additional monoatomic bridging by mda^{2鈭?/sup> or mdaH鈭?/sup> 渭- and 渭₃-O atoms on each edge and at the center of the Mn₃ triangular units gives a defective-dicubane core structure. Ligation is completed by two bridging and two monodentate pc鈭?/sup> groups, each of which is involved in 蟺-蟺 stacking interactions with those on neighboring Mn₄ molecules to give a 2D network. Variable-temperature solid-state magnetic susceptibility studies of 3 and 4 in the temperature range 5.0-300 K. Various fitting and simulation models were employed in analyzing the data for 3, which shows no evidence of significant intermolecular interactions, and it was concluded that it contains three symmetry-inequivalent exchange interactions, J = +2.34 cm鈭?, J鈥?#xA0;= +7.70 cm鈭?, J鈥?#xA0;= 鈭?.33 cm鈭? and g = 1.99, where J鈥?is the MnIII鈰疢nIII interaction, and J and J鈥?are the MnII鈰疢nIII interactions. This indicates an S = 8 ground state with a very low-lying an S = 9 excited state. This conclusion was supported by fits of reduced magnetization data, which gave an S = 8 ground state with axial zero-field splitting parameter D = 鈭?.19(1) cm鈭?, and g = 1.94(1). Ac susceptibility studies on 3 show that it is a single-molecule magnet (SMM). Complex 4 shows different magnetic behavior from 3 due to the intermolecular interactions.}