Asymmetrical modification of Keggin polyoxometalates by sextuple Ag–N coordination polymeric chains: Synthesis, structure and selective separation of cationic dyes

A new coordination polymeric chains modified polyoxometalate, H3K2[Ag5(DTB)5][SiW12O40]2·Cl2·8H2O (1) {DTB ​= ​1,4-di(1H-1,2,4-triazol-1-yl)benzene}, has been successfully synthesized under hydrothermal conditions. Single crystal X-ray diffraction analyses reveal that the Keggin POM cluster is modified by {Ag(DTB)}n chains in an unusually [2 ​+ ​4] asymmetrical mode resulting in a 2D double layer structure. By connection of K cations and π···π interactions between adjacent {Ag(DTB)}n coordination polymeric chains, the 2D structure extends to a 3D structure. In addition, crystal 1 can be used as a packing material for the highly selective adsorption and separation cationic dyes such as methylene blue (MB) and crystal violet (CV) against with methyl orange (MO) anionic dyes. The adsorption of a series of cationic organic dyes experiment demonstrated that this process is highly related to the sizes of organic dyes.