The magnetic Mobius strip: Synthesis, structure, and magnetic studies of odd-numbered antiferromagnetically coupled wheels
The magnetic Mobius strip: Synthesis, structure, and magnetic studies of odd-numbered antiferromagnetically coupled wheels
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DOI：
10.1002/anie.200460211
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发表时间：
2004-01-01
影响因子：
16.6
通讯作者：
Winpenny, REP
中科院分区：
文献类型：
--
作者：
Cador, O;Gatteschi, D;Winpenny, REP
先前报道的循环3d金属结构，从第一个（利帕德和同事的铁轮）到最大的，都包含偶数个金属中心很少有大于3的奇数环结构；它们都是五金属的，具有多齿不灵活的配体Raptis和他的同事最近报道了一个九元环，但只是作为高核结构的一部分很难解释为什么没有奇数的轮子，特别是奇数的金属圈，也就是以另一个金属阳离子为中心的轮子，是已知的这是特别令人沮丧的，因为这种轮子的磁性应该对对磁性挫折感兴趣的物理学家非常感兴趣反过来，自旋挫折在高温超导体和CMR材料等各种领域都很重要在这里，我们报告了第一个详细的磁性表征奇数轮大于一个三角形。合成的新分子物种使我们能够在介观尺度上研究挫败感，在介观尺度上量子计算仍然是可能的；希望在这里获得的理解以后可以更普遍地应用于其他受挫的系统。在之前的一篇论文[9]中，我们已经展示了如何利用[Cr8F8 (O2CCMe3) 16]的化学性质来生产一系列异金属类似物[R2NH2][Cr7MF8 (O2CCMe3) 16]，其中M= NiII 1, CoII， MnII或FeII和R可以是从甲基到正烷基的一系列烷基。仲铵离子被发现包裹在金属轮内，这表明，如果我们改变阳离子的大小，我们就可以改变轮子的大小。水合氟化铬（iii）与碱式碳酸镍在戊酸中二环己胺存在下反应，THF/甲苯结晶生成形状良好的六方晶体。元素分析和电喷雾质谱（ESMS）为[(C6H11) 2NH2][Cr8Ni-F9 (O2CCMe3) 18] 2的形成提供了令人信服的证据。2的ESMS谱在负离子谱中有一个阴离子轮的峰，在正离子谱中有两个显著的峰，分别是分子离子加一个钠离子和环加两个钠离子。这些是唯一显著的高质量峰值。2的晶体看起来是单一的，但x射线衍射模式有一个特殊的分布。适当的布拉格衍射点是在一个相当平坦的球体形状的倒易空间内发现的，并且在垂直于六倍晶体旋转轴的倒易平面上具有明显的漫射散射。这使得很难整合布拉格强度来确定结构因素，从而也产生了分配空间群的问题。该结构既可以在某些六边形空间群中描述，也可以在正交Pbna空间群中描述，这使得积分反射的内部R值更低。在Pbna中求解结构揭示了一个由单原子桥接的非金属核心。通过随后的最小二乘细化和差分傅里叶方法，可以确定最近邻八面体配位球的原子位置，但不能进一步发展原子结构。毫无疑问，私人配体的外部部分有很多紊乱。Bragg强度和漫射散射分布的综合信息支持以下结构模型：具有九元环的分子形成层，这些分子堆叠形成紧密排列的柱。在倒平面上的漫射散射分布…
The previously reported cyclic 3d-metal structures, from the first—the ferric wheel of Lippard and co-workers [1]—to the largest all contain an even number of metal centres.[2] There are very few odd-numbered cyclic structures larger than three; all are pentametallic and feature polydentate inflexible ligands.[3] Raptis and co-workers have very recently reported a nine-membered ring but only as part of higher nuclearity structures.[4] It is difficult to rationalize the absence of oddnumbered wheels, especially as odd-numbered metallocrowns, that is, wheels centered with a further metal cation, are known.[5] This is particularly frustrating because the magnetic properties of such wheels should be of great interest to physicists interested in magnetic frustration.[6] Spin frustration is, in turn, important in areas as diverse as high temperature superconductors [7] and CMR materials.[8] Herein we report the first detailed magnetic characterization of an odd-numbered wheel larger than a triangle. The new molecular species synthesized allows us to study frustration at a mesoscopic scale at which quantum calculations are still possible; hopefully the understanding gained here can later be applied more generally to other frustrated systems. In a preceding paper [9] we have shown how the chemistry of [Cr8F8 (O2CCMe3) 16] can be exploited to produce a series of heterometallic analogues [R2NH2][Cr7MF8 (O2CCMe3) 16], in which M= NiII 1, CoII, MnII, or FeII and R can be a range of alkyl groups from methyl to n-octyl. The secondary ammonium cation is found encapsulated within the metal wheel, and this suggested that if we varied the size of the cation we might be able to vary the size of the wheel. The reaction of hydrated chromium (iii) fluoride with basic nickel carbonate in pivalic acid in the presence of dicyclohexylamine, followed by crystallization from THF/toluene produced well-shaped hexagonal crystals. Elemental analysis and electrospray mass spectroscopy (ESMS) provide convincing evidence for the formation of [(C6H11) 2NH2][Cr8Ni-F9 (O2CCMe3) 18] 2. The ESMS spectrum of 2 contains a peak for the anionic wheel in the negative-ion spectrum and two significant peaks in the positive-ion spectrum for the molecular ion plus one sodium as well as for the ring plus two sodium ions. These are the only significant high-mass peaks. The crystals of 2 appear to be single, but the X-ray diffraction pattern has an extraordinary distribution. Proper Bragg diffraction spots are found within a rather flat spheroidal shaped volume of reciprocal space and with pronounced diffuse scattering in the reciprocal planes perpendicular to the apparent sixfold crystal axis of rotation. This makes it difficult to integrate the Bragg intensities for determining structure factors and thus also creates a problem in assigning the space group. The structure can either be described in some hexagonal space groups or in the orthorhombic Pbna space group, which gives the lower internal R value of integrated reflections. Solving the structure in Pbna reveals a nona-metallic core, bridged by single atoms. Atoms of the nearest-neighbor octahedral coordination sphere can be located but the atomic structure does not develop further by subsequent least-squares refinement and difference Fourier methods. Undoubtedly there is much disorder of the outer parts of the pivalate ligands. The combined information of Bragg intensities and distribution of diffuse scattering supports the following model of the structure: The molecules that have a nine-membered ring form layers, and these molecules are stacked to form columns that are close-packed. The distribution of diffuse scattering over the reciprocal plane …