pH-Controlled assembly of [ZnWO]-based hybrids from a 0D dimer to a 2D network: synthesis, crystal structure, and photocatalytic performance in transformation of toluene into benzaldehyde.

Polyoxometalate-based organic-inorganic hybrids have attracted considerable attention due to their fascinating structures and wide application prospects. In this work, using the same building blocks, ligands and metal ions (ZnWO(ZnW), 2,2'-bipyridine (2,2'-bipy), and Cu), we synthesized three new POM-based hybrids by controlling the pH values of the reaction systems. These three compounds {(Zn(H)WO)[Cu(2,2'-bipy)(HO)][Cu(2,2'-bipy)(HO)][Cu(2,2'-bipy)(HO)]}·6HO (1), (MeN){ZnWO[Cu(2,2'-bipy)(HO)][Cu(2,2'-bipy)(HO)]}·5HO (2), and {(Zn(H)WO)[Cu(2,2'-bipy)][Cu(2,2'-bipy)(HO)][Cu(2,2'-bipy)(HO)]}·5HO (3) have been structurally characterized by single-crystal X-ray diffraction. Compound 1 appears as a dimeric cluster structure, while compounds 2 and 3 appear as a 1D chain structure and a 2D network, respectively. The semiconducting properties of compounds 1-3 are different, which was demonstrated by band gap () and photocurrent response measurements. Compound 3 can efficiently catalyze the photooxidation of toluene to benzaldehyde with high selectivity using molecular oxygen as the oxidant component. Moreover, compound 3 was recycled and reused three times without significant degradation in conversion and selectivity. In addition, the mechanism of the photocatalytic reaction was also investigated.