Metal-Regulated Different [TeMo ₆ O ₂₄ ] 6 – -Based MOCs with Viologen Ligand for Catalytic Reduction of Cr(VI) and Oxidation of CEES under Multi-Wavelength Irradiation

Three new dual-functional polyoxometalate(POM)-based metal-organic complexes (POMOCs): {H₂[Zn₂(bcbpy)₂(H₂O)₈](TeMo₆O₂₄)}·10H₂O (BHU-10, HbcbpyCl = 1-(4-carboxybenzyl)-4,4'-bipyridinium), {H₂[Cu₂(bcbpy)₂(H₂O)₈](TeMo₆O₂₄)}·10H₂O (BHU-11), and H₂[Co₂(bcbpy)₂(TeMo₆O₂₄)(H₂O)₆]·6H₂O (BHU-12) were successfully synthesized. The central metal ion significantly modulates the structure: BHU-10 (Zn) and BHU-11 (Cu) adopt identical "sandwiched" structures comprising two [M₂(bcbpy)₂(H₂O)₈]⁴⁺ units and a free [TeMo₆O₂₄]⁶⁻ cluster, whereas the Co-based BHU-12 exhibits a distinct "zig-zag" structure with two [Co(bcbpy)(H₂O)₃]²⁺ units bridged by [TeMo₆O₂₄]⁶⁻ cluster. In photocatalytic Cr(VI) reduction and CEES oxidation under multiwavelength irradiation, BHU-12 significantly outperformed both BHU-10 and BHU-11. Under visible light, BHU-12 reduced 96% of Cr(VI) to Cr(III) within 90 min and oxidized CEES with 99% conversion and 99% selectivity in just 1 h. Furthermore, BHU-12 maintained stable catalytic activity after three cycles, demonstrating excellent structural stability and recyclability. The superior performance originates from BHU-12's unique "zig-zag"-type architecture. Compared to the "sandwiched" structure of BHU-10/11, the open-ring "zig-zag" configuration of BHU-12 facilitates better exposure of catalytic active sites. Additionally, the intrinsic properties of the central cobalt metal may contribute positively to the catalytic ability of BHU-12. A series of characterizations consistently confirmed that BHU-12 possesses superior photogenerated carrier separation and migration efficiency. The detailed mechanisms of the photocatalytic Cr(VI) reduction and CEES oxidation were studied.