Three Co
II octaazacryptates, with different substituents on the aromatic rings (Br, NO
2, CCH), were synthesised and characterised. These and the already published non-substituted cryptate catalysed CO
2 photoreduction to CO and CH
4 under blue visible light at room temperature. Although CO was observed after short irradiation times and a large range of catalyst concentrations, CH
4 was only observed after longer irradiation periods, such as 30 h, but with a small catalyst concentration (25 nm ). Experiments with
13C labelled CO
2 showed that CO is formed and reacts further when the reaction time is long. The CCH catalyst is deactivated faster than the others and the more efficient catalyst for CH
4 production is the one with Br. This reactivity trend was explained by an energy decomposition analysis based on DFT calculations.
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