Spin State in Homoleptic Iron(II) Terpyridine Complexes Influences Mixed Valency and Electrocatalytic CO2 Reduction

SUHR, SIMON; SCHRÖTER, NICOLAI; KLEOFF, MERLIN; NEUMAN, NICOLAS; HUNGER, DAVID; WALTER, ROBERT; LÜCKE, CLEMENS; STEIN, FELIX; DEMESHKO, SERHIY; LIU, HANG; REISSIG, HANS-ULRICH; VAN SLAGEREN, JORIS; SARKAR, BIPRAJIT

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Año: 2023 vol. 62 p. 6375 - 6386

0020-1669

Two homoleptic Fe(II) complexes in different spin states bearing superbasic terpyridine derivatives as ligands are investigated to determine the relationship between spin state and electrochemical/spectroscopic behavior. Antiferromagnetic coupling between a ligand-centered radical and the high-spin metal center leads to an anodic shift of the first reduction potential and results in a species that shows mixed valency with a moderately intense intervalence-charge-transfer band. The differences afforded by the different spin states extend to the electrochemical reactivity of the complexes: while the low-spin species is a precatalyst for electrocatalytic CO2 reduction and leads to the preferential formation of CO with a Faradaic efficiency of 37%, the high-spin species only catalyzes proton reduction at a modest Faradaic efficiency of approximately 20%.