Cation-Dependent Photocatalytic Conversion of CO₂ to Formic Acid and Formaldehyde by 1D Coordination Polymers

Photochemical carbon dioxide (CO2) reduction provides a pathway to sustainable chemicals such as formic acid (HCOOH) and formaldehyde (HCHO). However, the demand for high photon energy is still a major challenge. In this work, two new Ni(II)- and Mn(II)-based one-dimensional coordination polymers, (1D CPs) [Ni(9-aca)2(pdb)(H2O)2]·(EtOH) (CP1) and [Mn(9-aca)2(pdb)(CH3OH)(H2O)]·(H2O) (CP2) (H2aca = 9-anthracenecarboxylic acid and pdb = N,N′-bis(1-pyridine-4-yl-ethylidene)), have been synthesized. These act as potential catalysts and produce HCOOH and HCHO as value-added chemicals. The photocatalysis shows the reduction of CO2 to HCOOH and HCHO with maximum production rates for CP1 and CP2 of 47.7 mmol gcat–1h–1 and 44.3 mmol gcat–1h–1 for the formation of HCOOH, respectively, and 366 mmol gcat–1h–1 and 943 mmol gcat–1h–1 for HCHO, respectively. Here, the Ni-based CP1 catalyst stabilizes formate intermediates (HCOO–) via strong metal interactions, promoting their protonation to HCOOH by preventing over-reduction. In contrast, the Mn-CP2 catalyst offers weaker stabilization, leading to further CO2 reduction and increased HCHO formation. However, the catalysts are recyclable for multiple reaction cycles without losing their structural stability or efficiency.