Photocatalytic Carbon Dioxide Reduction and Density Functional Theory Investigation of 2,6-(Pyridin-2-yl)-1,3,5-triazine-2,4-diamine and Its Cobalt and Nickel Complexes

Carbon dioxide (CO₂) is an important trace gas in Earth’s atmosphere. Its high concentration in the environment causes serious problems. Thus, it has become imperative to develop efficient ways to reduce CO₂. One of the best strategies to transform this greenhouse gas is the use of solar energy for the photochemical reduction of CO₂. However, this process is challenging due to a number of drawbacks that should be overcome for it to become a promising alternative for generation of sustainable fuels and chemicals. In this work, we have engineered molecular photocatalysts based on 2,6-(Pyridin-2-yl)-1,3,5-triazine-2,4-diamine 1 which mimic [2,2′;6′,2′′]terpyridine (tpy) and its related complexes by coordination with transition metal ions. Because of the functional groups (-NH₂ group) and the electronic structural modification of 1 as compared with tpy, remarkable photocatalytic properties over the CO₂ reduction to CO were found for the free and metal ligands with turnover numbers (TONs) between 80–102 with BIH and 480–1370 with BID. An integrated method using structural characterization by X-ray diffraction analysis, experimental and density functional theory calculations was used to track the mechanistic pathways of the photocatalytic CO₂ reduction reaction.