Syntheses, structures, photochromic and photocatalytic properties of two viologen-polyoxometalate hybrid materials

Two new viologen - polyoxometalate hybrid crystalline materials: (MV)₂[HPW^Ⅴ₂W^Ⅵ₁₀O₄₀] ·2H₂O (1) and (EV)₂[Mo₈O₂₆] (2) have been synthesized by using the cations of 1,1′-dimethyl-4,4′-bipyridinium dichloride (methyl viologen, MV) and 1,1′-diethyl-4,4′-bipyridinium dibromide (ethyl viologen, EV) as the electron acceptors, and the electron-rich polyoxometalate anions as the electron donors. The structures of compounds 1 and 2 have been deter- mined by single-crystal X-ray crystallography. Hydrogen bond interactions exist between the cations and the anions in 1 and 2. Interestingly, 2 has a photochromic performance with a light response time within 1 min. The photochro- mic mechanism of compound 2 has been investigated by solid-state diffuse reflection, electron paramagnetic reso- nance and theoretical calculation. 1 and 2 show good catalytic performance in the photocatalytic degradation of sev- eral organic dyes (methylene blue, pararosaniline hydrochloride and rhodamine 6G). CCDC: 2252398, 1; 2252396, 2.