Coordination Assemblies of [Mn4] Single-Molecule Magnets Linked by Photochromic Ligands: Photochemical Control of the Magnetic Properties
Coordination Assemblies of [Mn4] Single-Molecule Magnets Linked by Photochromic Ligands: Photochemical Control of the Magnetic Properties
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DOI：
10.1021/ja903366d
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发表时间：
2009-07-22
影响因子：
15
通讯作者：
Irie, Masahiro
中科院分区：
文献类型：
--
作者：
Morimoto, Masakazu;Miyasaka, Hitoshi;Irie, Masahiro
为了实现单分子磁体磁性的可逆光开关，混合价四核[合成了由二芳基乙烯类光致变色配体的开环和闭环异构体连接的[Mn-4（hmp）（6）（dae-o）（2）（ClO 4）（2）]配合物：[Mn-4（hmp）（6）（dae-o）（2）（ClO 4）（2）]（开环形式; 1 o）和[Mn-4（hmp）（6）（dae-c）（2）（H2O）（2）]（ClO 4）（2）中心点CH 3CN中心点4 H（2）O（闭环形式; 1c），其中Hhmp是2-羟甲基吡啶，H（2）dae-o和H（2）dae-c是1的开环和闭环异构体，分别为2-双（5-羧基-2-甲基-3-噻吩基）全氟环戊烯（H（2）dae）。从X射线晶体学分析，1 o和1c具有一维（1-D）链结构与[-{Mn-4}-（dae）-]的重复单元，其中[Mn-4]单元由二芳基乙烯配体通过羧酸酯基团配位到Mn-II位点桥接。直流和交流磁测量结果表明，一维链中的[Mn-4]团簇由于两种团簇内铁磁交换相互作用而具有S-T = 9的基态，表现为SMM。1 o和1c在晶相中都发生了光致变色反应，在紫外光和可见光照射下，它们的颜色在红棕色和蓝色之间可逆地变化。对于1 o，没有观察到显着的变化后，通过UV照射的dae-o部分的光环化的磁性能。与此相反，dae-c部分通过可见光照射的光环化增强了1c中的[Mn-4]单元间相互作用，这是由光反应期间二芳基乙烯部分的几何变化和相邻1-D链之间的[Mn-4]排列的后续变化引发的。这项工作说明了有用的光致变色分子的光开关复合物的磁行为，甚至超顺磁性系统，与SMM单元。
To achieve reversible photoswitching of the magnetic properties of single-molecule magnets (SMMs), coordination assemblies of a mixed valence tetranuclear [(Mn2Mn2III)-Mn-II] complex linked by open-and closed-ring isomers of a photochromic diarylethene ligand were synthesized: [Mn-4(hmp)(6)(dae-o)(2)(ClO4)(2)]center dot 6H(2)O (open-ring form; 1o) and [Mn-4(hmp)(6)(dae-c)(2)(H2O)(2)](ClO4)(2)center dot CH3CN center dot 4H(2)O (closed-ring form; 1c), where Hhmp is 2-hydroxymethylpyridine, and H(2)dae-o and H(2)dae-c are open- and closed-ring isomers of 1,2-bis(5-caxboxyl-2-methyl-3-thienyl)perfluorocyclopentene (H(2)dae), respectively. From X-ray crystallographic analyses, 1o and 1c have one-dimensional (1-D) chain structures with a repeating unit of [-{Mn-4}-(dae)-], in which the [Mn-4] units are bridged by the diarylethene ligands coordinated to the Mn-II sites via carboxylate groups. Magnetic measurements involving direct-current (dc) and alternating-current (ac) techniques showed that each [Mn-4] cluster in the 1-D chains had an S-T = 9 ground state due to two kinds of intracluster ferromagnetic exchange interactions and behaved as SMMs. Both 1o and 1c underwent photochromic reactions in the crystalline phase, and their colors reversibly changed between reddish-brown and blue upon irradiation with ultraviolet (UV) and visible light. For 1o, no significant change in the magnetic properties was observed after the photocyclization of the dae-o moiety by UV irradiation. In contrast, the photocycloreversion of the dae-c moiety by visible irradiation enhanced inter-[Mn-4] unit interactions in 1c, which was triggered by the geometrical change in the diarylethene moiety during the photoreaction and the subsequent change in the inter-[Mn-4] arrangement between the neighboring 1-D chains. This work illustrates the usefulness of photochromic molecules for photoswitching the magnetic behavior of complexes, even superparamagnetic systems, with SMM units.