Striking Differences in Properties of Geometric Isomers of [Ir(tpy)(ppy)H] + : Experimental and Computational Studies of their Hydricities, Interaction with CO 2 , and Photochemistry

We prepared two geometric isomers of [Ir(tpy)(ppy)H] + , previously proposed as a key intermediate in the photochemical reduction of CO 2 to CO, and characterized their notably different ground‐ and excited‐state interactions with CO 2 and their hydricities using experimental and computational methods. Only one isomer, C‐trans‐ [Ir(tpy)(ppy)H] + , reacts with CO 2 to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH 3 CN/TEOA, a common reactive C‐trans ‐[Ir(tpy)(ppy)] 0 species, irrespective of the starting isomer or monodentate ligand (such as hydride or Cl), reacts with CO 2 and produces CO with the same catalytic efficiency.