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.