Solvothermal Assembly of a Series of Organic–Inorganic Hybrid Materials Constructed from Keggin Polyoxometalate Clusters and Copper(I)–Organic Frameworks

Seven polyoxometalate (POM) hybrid materials based on Keggin polyanion building blocks and copper(I)–organic frameworks with pyrazine derivatives, namely, [CuI4(2Et,3Me-Pyr)5(SiW12O40)] (1), [CuI4(2,6-Pyr)4(SiW12O40)] (2), [CuI4(2,5-Pyr)4(SiW12O40)(H2O)2] (3), [CuI4(2,3,5,6-Pyr)4(SiW12O40)](H2O) (4), [CuI4(2,5-Pyr)4(PMoVI11MoVO40)]·1.5H2O (5), [CuI3(2,3,5-Pyr)4(PMo12O40)]·H2O (6), and [CuI4(2Et,3Me-Pyr)5(PMoVI11MoVO40)] (7), where 2Et,3Me-Pyr = 2-ethyl-3-methylpyrazine, 2,6-Pyr = 2,6-dimethylpyrazine, 2,5-Pyr = 2,5-dimethylpyrazine, 2,3,5-Pyr = 2,3,5-trimethylpyrazine, and 2,3,5,6-Pyr = 2,3,5,6-tetramethylpyrazine, have been synthesized under solvothermal conditions. In 1 and 7, polyanions link CuI–organic sheets to generate 3D (3,4)-connected frameworks. In 2, the polyanion bridges CuI–organic chains to yield a 3D (3,4,6)-connected framework. Both 3 and 4 exhibit 2D double layer structures. In 5, the Keggin polyanion bridges the CuI–Pyr chains to form an infinite 3D (3,4)-connected framework. In 6, CuI cations are bridged by the 2,3,5-Pyr and Keggin polyanions to generate a novel 2D (8,3) sheet. The roles of the pyrazine derivatives and the Keggin polyanions in the formation of the POM-based MOFs have been discussed.

七种以Keggin型多阴离子（Keggin polyanion）为结构基元、结合含吡嗪衍生物的一价铜有机骨架的多金属氧酸盐（polyoxometalate, POM）杂化材料，其化学式分别为[CuI4(2Et,3Me-Pyr)5(SiW12O40)]（1）、[CuI4(2,6-Pyr)4(SiW12O40)]（2）、[CuI4(2,5-Pyr)4(SiW12O40)(H2O)2]（3）、[CuI4(2,3,5,6-Pyr)4(SiW12O40)](H2O)（4）、[CuI4(2,5-Pyr)4(PMoVI11MoVO40)]·1.5H2O（5）、[CuI3(2,3,5-Pyr)4(PMo12O40)]·H2O（6）以及[CuI4(2Et,3Me-Pyr)5(PMoVI11MoVO40)]（7）；其中2Et,3Me-Pyr代表2-乙基-3-甲基吡嗪，2,6-Pyr代表2,6-二甲基吡嗪，2,5-Pyr代表2,5-二甲基吡嗪，2,3,5-Pyr代表2,3,5-三甲基吡嗪，2,3,5,6-Pyr代表2,3,5,6-四甲基吡嗪，该系列材料均在溶剂热条件下合成。在化合物1与7中，多阴离子桥连一价铜有机片层，构建出具有(3,4)连接模式的三维骨架。在化合物2中，多阴离子桥连一价铜有机链，得到具有(3,4,6)连接模式的三维骨架。化合物3与4均呈现二维双层结构。在化合物5中，Keggin型多阴离子桥连一价铜-吡嗪链，形成具有(3,4)连接模式的无限三维骨架。在化合物6中，一价铜阳离子被2,3,5-三甲基吡嗪与Keggin型多阴离子桥连，得到新型的具有(8,3)连接模式的二维片层。本研究探讨了吡嗪衍生物与Keggin型多阴离子在该类多金属氧酸盐基金属有机骨架（POM-based MOFs）的形成过程中的作用。