Assembly of a basket-like {Sr ⊂ P6Mo18O73} cage from 0D dimmer to 2D network and its photo-/electro-catalytic properties

Abstract

A series of basket-like heteropoly blues, formulated as (H₄bth)[{Cu(H₂O)}₂{Sr ⊂ P₆Mo^V₂Mo^VI₁₆O₇₃}]·4H₂O (1), {H₂bih}₃[{Fe^II(H₂O)₂}{Sr ⊂ P₆Mo^V₂Mo^VI₁₆O₇₃}]·2H₂O (2), (H₂bih)₃[{Co^II(H₂O)₂}{Sr ⊂ P₆Mo^V₂Mo^VI₁₆O₇₃}]·2H₂O (3), (H₂bih)₃[{Ni^II(H₂O)₂}{Sr ⊂ P₆Mo^V₂Mo^VI₁₆O₇₃}]·2H₂O (4), (H₂bih)₂(H₂bip)[{Zn (H₂O)_0.5}{Sr ⊂ P₆Mo^V₂Mo^VI₁₆O₇₃}]·5.5H₂O (5), (bth = 1,6-bis(triazole)hexane; bih = 1,6-bis(imidazol)hexane; bip = 1,5-bis(imidazol)pentane) have been synthesized hydrothermally and fully characterized. The structural analysis shows that all the compounds contain two electron reduced polyanions [Sr ⊂ P₆Mo^V₂Mo^VI₁₆O₇₃]⁸⁻ (abbreviated as {P₆Mo₁₈O₇₃}), which consists of a tetra vacant γ-Dawson-type{P₂Mo₁₄} unit and a “handle”-shaped {P₄Mo₄} segment encapsulating a Sr²⁺ cation in the central cavity. Compound 1 is a 6-connected two-dimensional (2D) layer, which represents the first 2D assembly of basket-type polyoxometalates. Compounds 2–4 are isostructural one-dimensional zigzag chains linked by an M(H₂O)₂ linker (M = iron for 2, cobalt for 3, and nickel for 4). Compound 5 is a dimeric cluster supported by a binuclear {Zn₂(H₂O)} unit. The optical band gaps of 1–5 reveal their semiconductive natures. The compounds if used as photocatalysts exhibit a universal high efficiency degradation ability for dyes such as methylene blue, Rhodamine B, and Azon phloxine. The lifetime and reaction mechanism of the catalysts were investigated with a series of experiments. The compounds also show good bifunctional electrocatalytic behavior for the oxidation of ascorbic acid (AA) and reduction of nitrite ions.