Two-dimensional networks based on Mn4 complex linked by dicyanamide anion: from single-molecule magnet to classical magnet behavior.
Two-dimensional networks based on Mn4 complex linked by dicyanamide anion: from single-molecule magnet to classical magnet behavior.
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DOI：
10.1021/ja0574062
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发表时间：
2006-02
影响因子：
15
通讯作者：
H. Miyasaka;K. Nakata;L. Lecren;C. Coulon;Y. Nakazawa;T. Fujisaki;K. Sugiura;M. Yamashita;
中科院分区：
文献类型：
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作者：
H. Miyasaka;K. Nakata;L. Lecren;C. Coulon;Y. Nakazawa;T. Fujisaki;K. Sugiura;M. Yamashita;
合成了三种基于通过二氰胺 (dcn-) 连接体连接的 Mn(III)/Mn(II) 四核单分子磁体 (SMM) 的二维 (2D) 网络化合物：[Mn4(hmp)4(Hpdm)2(dcn)2](ClO4)2 x 2 H2O x 2 MeCN (2)， [Mn4(hmp)4Br2(OMe)2(dcn)2] x 0.5 H2O x 2 THF (3)、[Mn4(hmp)6(dcn)2](ClO4)2 (4)，其中 Hhmp 和 H2pdm 分别是 2-羟甲基吡啶和吡啶-2,6-二甲醇。 [Mn4]/dcn-系统看起来非常通用，但可以通过合成条件的微调使其化学结构合理化。尽管其 Mn(II) 配位层发生了很大的改变，但整个化合物家族中都保留了双立方 [Mn4] 单元。对 Mn(II) 位点上 dcn- 配位数的化学控制是获得以下系列化合物的关键：离散簇 [Mn4(hmp)6(NO3)2(dcn)2] x 2 MeCN (1)、2D 网络（2、3 和 4）以及之前报道的 3D 化合物， [Mn4(hmp)4(mu3-OH)2][Mn(II)(dcn)6] x 2 MeCN x THF。直流磁测量表明，Mn2+-Mn3+ 和 Mn3+-Mn3+ [Mn4] 内磁相互作用都是铁磁性的，导致 [Mn4] 单元的基态为 S(T) = 9。尽管 2-4 中的二维晶格非常相似，但 [Mn4] 单元的两种取向（即两个易轴之间的角度变化）导致不同的磁性，范围从 2 和 1 的 SMM 行为到 4 的长程倾斜反铁磁有序。化合物 3 更复杂，因为磁性测量强烈表明存在低于 2.1 K 的倾斜反铁磁有序，尽管 同时观察到磁化缓慢弛豫。热容测量证实了 4 中的长程磁序，而在 3 中，临界行为被各向异性 [Mn4] 单元的缓慢弛豫所冻结。
Three two-dimensional (2D) network compounds based on Mn(III)/Mn(II) tetranuclear single-molecule magnets (SMMs) connected by dicyanamide (dcn-) linkers have been synthesized: [Mn4(hmp)4(Hpdm)2(dcn)2](ClO4)2 x 2 H2O x 2 MeCN (2), [Mn4(hmp)4Br2(OMe)2(dcn)2] x 0.5 H2O x 2 THF (3), [Mn4(hmp)6(dcn)2](ClO4)2 (4), where Hhmp and H2pdm are 2-hydroxymethylpyridine and pyridine-2,6-dimethanol, respectively. The [Mn4]/dcn- system appears very versatile, but enables its chemistry to be rationalized by a fine-tune of the synthetic conditions. The double cuboidal [Mn4] unit is preserved in the whole family of compounds, despite strong modifications of its Mn(II) coordination sphere. The chemical control of the coordination number of dcn- on the Mn(II) sites has been the key to obtain the following series of compounds: a discrete cluster, [Mn4(hmp)6(NO3)2(dcn)2] x 2 MeCN (1), 2D networks (2, 3, and 4), and the previously reported 3D compound, [Mn4(hmp)4(mu3-OH)2][Mn(II)(dcn)6] x 2 MeCN x THF. Direct current magnetic measurements show that both Mn2+-Mn3+ and Mn3+-Mn3+ intra-[Mn4] magnetic interactions are ferromagnetic leading to an S(T) = 9 ground state for the [Mn4] unit. Despite the very similar 2D lattices in 2-4, the two kinds of orientation of the [Mn4] unit (i.e., angle variations between the two easy axes) lead to different magnetic properties ranging from SMM behavior for 2 and 1 to a long-range canted antiferromagnetic order for 4. Compound 3 is more complicated as the magnetic measurements strongly suggest the presence of a canted antiferromagnetic order below 2.1 K, although the magnetization slow relaxation is simultaneously observed. Heat capacity measurements confirm the long-range magnetic order in 4, while in 3, the critical behavior is frozen by the slow relaxation of the anisotropic [Mn4] units.