The behavior of water molecules in the nanocavities of the HKUST-1 framework: A combined quantum mechanical and vibrational spectroscopy investigation
Résumé
Abstract The discovery of molecular catalysts for the CO 2 reduction reaction (CO 2 RR) in the presence of water, which are both effective and selective towards the generation of carbon‐based products, is a critical task. Herein we report the catalytic activity towards the CO 2 RR in acetonitrile/water mixtures by a cobalt complex and its iron analog both featuring the same redox‐active ligand and an unusual seven‐coordination environment. Bulk electrolysis experiments show that the cobalt complex mainly yields formate (52 % selectivity at an applied potential of −2.0 V vs Fc + /Fc and 1 % H 2 O) or H 2 (up to 86 % selectivity at higher applied bias and water content), while the iron complex always delivers CO as the major product (selectivity >74 %). The different catalytic behavior is further confirmed under photochemical conditions with the [Ru(bpy) 3 ] 2+ sensitizer (bpy=2,2’‐bipyridine) and N,N‐diisopropylethylamine as electron donor, where the cobalt complex leads to preferential H 2 formation (up to 89 % selectivity), while the iron analog quantitatively generates CO (up to 88 % selectivity). This is ascribed to a preference towards a metal‐hydride vs. a metal‐carboxyl pathway for the cobalt and the iron complex, respectively, and highlights how metal replacement may effectively impact on the reactivity of transition metal complexes towards solar fuel formation.