Self-organization towards complex meso-helix in the structures of keggin-type polyoxometalate-based metal-organic frameworks for photocatalytic degradation of rhodamine B

For exploring the V-shape organic ligand influence on the fabrication of complex helices or meso-helices in polyoxometalate-based metal-organic frameworks (POMOFs), a crystalline hybrid with intricate meso-helix structure, H [K2Ag9(DPT)7 (u-2-O)2(H2O)4][SiW12O40]2 (1) {DPT = 2,5-di (pyridin-3-yl)-1,3,4-thiadiazole}, was successfully isolated under hydrothermal conditions. Compound 1 displays a complex meso-helix which is composed of two types of metal-organic subunits. Subunit A, is a non-planar S-shaped metal-organic chain that is constructed by five DPT ligands and four Ag cations, and subunit B is a planar S-shaped metal-organic unit that is built by two DPT ligands and three Ag cations. Further, subunit A and B are fused together in the A-B-A-B mode to generate an unprecedented meso-helix. The photocatalytic performance of compound 1 was evaluated by the RhB decorlorization. Under the UV light irradiation, the photocatalytic decolorization rate of RhB is 75.9% within 300 min, which is 1.82 times than pure (NBu4)4 [SiW12O40]. The cycle experiment shows that title compound has excellent stability after 5 cycles. In addition, the possible mechanism of the photocatalytic degradation has been fully discussed.