Covalent Linkage Engineering of a Bismuth Iodide Framework for Near-Infrared-Driven CO2-to-C2 Photoreduction in Aqueous Solution.

Near-infrared (NIR)-driven CO2 photoreduction to multi-carbon products remains highly challenging because effective utilization of low-energy NIR photons requires not only extended light harvesting but also efficient charge separation and transport, structural robustness, and accessible sites for C-C coupling. Although several bismuth halides exhibit narrow bandgaps and NIR absorption, translating such optical response into productive NIR photochemistry remains largely unexplored. Herein, we construct a covalent-linked bismuth iodide framework, BiI(tadt) (tadt = 1,3,4-thiadiazole-2,5-dithiolate), in which Bi-S covalent bonds bridge dimeric [Bi2I2]4+ clusters with π-conjugated tadt ligands to form an electronically delocalized framework. The Bi-S linkages enhance structural robustness, facilitate inorganic-organic orbital hybridization, and extend light absorption into the NIR region with a narrow bandgap of 1.44 eV. Photophysical studies and theoretical calculations reveal that linkage-mediated electronic coupling promotes carrier transport and NIR response, while adjacent Bi3+ sites within [Bi2I2]4+ clusters facilitate *CO coupling and stabilize key *OCCO intermediates. Consequently, single-component BiI(tadt) achieves NIR-driven CO2-to-C2 photoreduction in aqueous solution with an apparent quantum yield of 0.14% at 750(± 15) nm. This work demonstrates that covalent engineering of inorganic-organic connectivity bridges NIR absorption and productive multi-electron photochemistry, providing a design principle for lead-free metal halide photocatalysts utilizing low-energy solar photons.