Two Keggin polyoxometalate-based hybrid compounds with different helix: Syntheses, structure and catalytic activities

By adjusting pH value, two new Keggin polyoxometalate-based hybrid compounds with different helical structure, [Ag6(btp)(pyttz)6·(HSiMo12O40)2]·4H2O (1) and [Ag2(pyttz)4·(H2SiMo12O40)2]·(TMA)2·4H2O (2), (pyttz = 3-(pyrid-4-yl)-5-(1 H-1,2,4–3-yl)-1,2,4-triazolyl, btp = 5,5′-di(pyridin-4-yl)-1 H,1′H-3,3′-bi(1,2,4-triazole), TMA = tetramethylammonium), were successfully isolated by hydrothermal reaction and structurally characterized. Structural analysis shows the nature of the inorganic meso-helical channel in compound 1 and 2D homological helical layer in compound 2. It is also interesting that a new organic ligand btp is formed in situ by the coupling of N-Heterocycle in 1. In addition, the catalytic activities of 1 and 2 as solid-acid catalyst are explored, and the results indicate that 1 and 2 are a kind of highly-efficient and promising solid catalysts. Additionally, the proposed generation mechanism of btp in situ is also discussed.