Metal-Regulated Different [TeMo ₆ O ₂₄ ] ^{6 <b>–</b>} -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): {H 2 [Zn 2 (bcbpy) 2 (H 2 O) 8 ](TeMo 6 O 24 )}·10H 2 O ( BHU-10, HbcbpyCl = 1-(4-carboxybenzyl)-4,4′-bipyridinium), {H 2 [Cu 2 (bcbpy) 2 (H 2 O) 8 ](TeMo 6 O 24 )}·10H 2 O ( BHU-11 ), and H 2 [Co 2 (bcbpy) 2 (TeMo 6 O 24 )(H 2 O) 6 ]·6H 2 O ( 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 [M 2 (bcbpy) 2 (H 2 O) 8 ] 4+ units and a free [TeMo 6 O 24 ] 6– cluster, whereas the Co-based BHU-12 exhibits a distinct “zig-zag” structure with two [Co(bcbpy)(H 2 O) 3 ] 2+ units bridged by [TeMo 6 O 24 ] 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.