Effects of Pyridine Ligands on the Structure and Reactivity of Cu ₃ O ⁺ Clusters toward CO ₂

Understanding the ligand effects of organic ligand-protected copper clusters toward CO 2 is a prerequisite for improving their rational design for CO 2 capture and conversion. In this work, the regulatory roles of pyridine ligands on the structure of Cu 3 O + in Cu 3 OPy n + ( n = 0–3) clusters and their reactivity toward CO 2 were investigated through a combination of mass spectrometry and density functional theory (DFT) calculations. Experimental results reveal that pyridine ligands significantly modulate CO 2 adsorption capacity and rate: the Cu 3 O + cluster adsorbs up to three CO 2 molecules; Cu 3 OPy + and Cu 3 OPy 2 + adsorb a maximum of two and one, respectively; and Cu 3 OPy 3 + shows no adsorption. Notably, the pyridine-ligated Cu 3 OPy 1–2 + clusters exhibit reactivity approximately 2 orders of magnitude higher than the bare Cu 3 O + cation, with Cu 3 OPy + being the most reactive one among all four Cu 3 OPy 0–3 + clusters. DFT calculations indicate that the ligand-induced enhanced reactivity originates from the increased polarity, enlarged effective collision cross section (CCS), and added vibrational degrees of freedom (DOF) rather than CO 2 adsorption energy or charge transfer. These conclusions were further supported by reactions between CuPy 0–3 + clusters and CO 2 . This study revealed the ligand effects on the structures and reactivity of copper-based clusters toward CO 2 at the atomic level, providing useful insights for the design of efficient ligand-protected cluster catalysts for CO 2 capture and conversion.