Striking Differences in Properties of Geometric Isomers of [Ir(tpy)(ppy)H](+): Experimental and Computational Studies of their Hydricities, Interaction with CO2, and Photochemistry.

We prepared two geometric isomers of [Ir(tpy)(ppy)H](+), previously proposed as a key intermediate in the photochemical reduction of CO2 to CO, and characterized their notably different ground- and excited-state interactions with CO2 and their hydricities using experimental and computational methods. Only one isomer, C-trans-[Ir(tpy)(ppy)H](+), reacts with CO2 to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH3CN/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 CO2 and produces CO with the same catalytic efficiency.