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.