Inclusion of viologen cations leads to switchable metal-organic frameworks
Inclusion of viologen cations leads to switchable metal-organic frameworks
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DOI：
10.1039/c9fd00137a
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发表时间：
2021-02-01
影响因子：
3.4
通讯作者：
Burrows, Andrew D.
中科院分区：
文献类型：
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作者：
Cadman, Laura K.;Mahon, Mary F.;Burrows, Andrew D.
在DMF中，Zn(NO3)(2)中心点6H(2)O与多羧酸1,3-苯二羧酸（H(2)mbdc）、1,4-苯二羧酸（H(2)bdc）、1,3,5-苯三羧酸（H(3)btc）和4,4 '-联苯二羧酸（H(2)bpdc）在碘化紫紫甲基（[MV]I-2）存在下反应得到了以紫紫甲基为反离子的阴离子框架。在120℃的反应条件下，生成了蓝色产物[MV][Zn-3(mbdc)(4)] （1-ht）、[MV](0.44)[H2MV](0.36)[NMe2H2](0.4)[Zn-3(bdc)(4)]中心点0.6DMF （2-ht）、[MV](0.5)[Zn(btc)]中心点DMF （4-ht）和[MV][Zn-4(bpdc)(5)]中心点8DMF中心点10H(2)O (5-ht)，这些产物含有自由基阳离子[MV]（+）。相反，在85℃下进行同样的反应，得到含有指示式[MV]（2+）的橙色同构化合物。与溴化紫乙酯的反应也有类似的观察结果。化合物1-ht， 2-ht和4-ht具有类似的框架拓扑结构，其中NMe2H2+是包含的阳离子。相比之下，5-ht基于以前未报道的互渗透网络。化合物2-ht除含有[MV]（+）外还含有质子化物质[H2MV](2+)，晶体结构表明前者的两个环相互交错。该物种被认为是在合成中使用的反应条件下形成的，并且使用另一种方法抑制了[H2MV]（2+）的形成，该方法是由紫紫二乙酸原位形成紫紫甲基。在含bdc的产品中，暴露于空气中，自由基阳离子被迅速氧化成阳离子，其颜色由蓝色变为橙色。这种变化可以通过加热到120摄氏度或暴露于紫外线辐射来逆转，这两种方法都是在氮气下进行的。这与mbdc和btc类似物1-ht和4-ht的观察结果相反，因为在这些化合物中，蓝色持续数周。这种差异可能与结构有关，2-ht中存在的通道允许氧到达自由基阳离子。
The reactions of Zn(NO3)(2)center dot 6H(2)O with the polycarboxylic acids 1,3-benzenedicarboxylic acid (H(2)mbdc), 1,4-benzenedicarboxylic acid (H(2)bdc), 1,3,5-benzenetricarboxylic acid (H(3)btc) and 4,4 '-biphenyldicarboxylic acid (H(2)bpdc) in the presence of methyl viologen iodide ([MV]I-2) in DMF gave anionic frameworks with methyl viologen species incorporated as counter-ions. When the reactions were carried out at 120 degrees C, the blue products [MV][Zn-3(mbdc)(4)] (1-ht), [MV](0.44)[H2MV](0.36)[NMe2H2](0.4)[Zn-3(bdc)(4)]center dot 0.6DMF (2-ht), [MV](0.5)[Zn(btc)]center dot DMF (4-ht) and [MV][Zn-4(bpdc)(5)]center dot 8DMF center dot 10H(2)O (5-ht) were formed, and these were shown to contain the radical cation [MV](+). In contrast, the same reactions carried out at 85 degrees C gave orange isostructural compounds containing the dication [MV](2+). Similar observations were made for reactions with ethyl viologen bromide. The compounds 1-ht, 2-ht and 4-ht contain similar framework topologies to analogues in which NMe2H2+ is the included cation. In contrast, 5-ht is based on a previously unreported interpenetrated network. Compound 2-ht contains the protonated species [H2MV](2+) in addition to [MV](+) and the crystal structure shows that the two rings in the former are staggered with respect to each other. This species is believed to form under the reaction conditions employed in the synthesis and the formation of [H2MV](2+) is suppressed by using an alternative approach in which methyl viologen is formed in situ from viologen diacetic acid. In the bdc-containing products, the radical cation is rapidly oxidised to the dication on exposure to air, as witnessed by the colour change from blue to orange. This change is reversed either by heating to 120 degrees C or exposure to UV radiation, both under nitrogen. This is in contrast to observations with the mbdc and btc analogues 1-ht and 4-ht, as in these compounds the blue colour persists for weeks. The difference can be related to the structures, with the channels present in 2-ht allowing oxygen to reach the radical cations.