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.