Linkage Isomerism and Spin Frustration in Heterometallic Rings: Synthesis, Structural Characterization, and Magnetic and EPR Spectroscopic Studies of Cr7Ni, Cr6Ni2, and Cr7Ni2 Rings Templated About Imidazolium Cations
Linkage Isomerism and Spin Frustration in Heterometallic Rings: Synthesis, Structural Characterization, and Magnetic and EPR Spectroscopic Studies of Cr7Ni, Cr6Ni2, and Cr7Ni2 Rings Templated About Imidazolium Cations
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DOI：
10.1002/chem.200901938
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发表时间：
2009-01-01
影响因子：
4.3
通讯作者：
Winpenny, Richard E. P.
中科院分区：
文献类型：
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作者：
Boeer, Angelika B.;Collison, David;Winpenny, Richard E. P.
报道了以咪唑鎓阳离子为模板的三个异金属环的合成和结构表征。这些化合物为 [2,4-DiMe-ImidH][(Cr7NiF8)-F-II(O(2)CtBu)(16)] 1 (2,4-DiMe-ImidH = 2,4-二甲基咪唑的阳离子)、[ImidH](2)[Cr6Ni2II-F-8(O(2)CCtBu)(16)] 2 (ImidH = 的阳离子咪唑)和[1-Bz-ImidH](2) [(Cr7Ni2F9)-F-II(O(2)CtBu)(18)] 3 (1-Bz-Imid H = 1-苯甲基咪唑的阳离子)。该结构显示 1 和 2 形成金属八角形阵列，3 形成金属中心九角形阵列。在所有情况下，多边形的边缘均由单个氟化物和两个新戊酸配体桥接，并且二价金属中心的位置无法通过 X 射线衍射来区分。磁性研究与 EPR 光谱相结合，可以表征化合物的磁性状态。在每种情况下，交换都是反铁磁性的，磁交换参数 J 近似为 -5.8 cm(-1)，并且不可能区分两个 Cr-III 中心 (J(CrCr)) 之间的交换与 Cr-III 和 Ni-II 中心 (J(CrNi)) 之间的交换。对于2，有证据表明异金属环存在至少两个、可能四个连接异构体，这是由环中存在两个二价金属中心引起的。 3 的 EPR 光谱表明环的基态为 S=1/2，并且可能仅存在一种连接异构体。
The synthesis and structural characterization of three heterometallic rings templated about imidazolium cations is reported. The compounds are [2,4-DiMe-ImidH][(Cr7NiF8)-F-II(O(2)CtBu)(16)] 1 (2,4-DiMe-ImidH = the cation of 2,4-dimethylimidazole), [ImidH](2)[Cr6Ni2II-F-8(O(2)CCtBu)(16)] 2 (ImidH = the cation of imidazole), and [1-Bz-ImidH](2) [(Cr7Ni2F9)-F-II(O(2)CtBu)(18)] 3 (1-Bz-Imid H = the cation of 1-benzylimidazole). The structures show the formation of octagonal arrays of metals for 1 and 2 and a nonagon of metal centers for 3. In all cases the edges of the polygon are bridged by a single fluoride and two pivalate ligands, and the position of the divalent metal centers cannot be distinguished by X-ray diffraction. Magnetic studies combined with EPR spectroscopy allow the characterization of the magnetic states of the compounds. In each case the exchange is antiferromagnetic with a magnetic exchange parameter J approximate to -5.8 cm(-1), and it is not possible to differentiate the exchange between two Cr-III centers (J(CrCr)) from the exchange between a Cr-III and a Ni-II center (J(CrNi)). For 2 there is evidence for the presence of at least two, possibly four, linkage isomers of the heterometallic ring, caused by the presence of two divalent metal centers in the ring. The EPR spectroscopy of 3 suggests an S=1/2 ground state of the ring and that it is likely that only one linkage isomer is present.