Anion photoelectron imaging and theoretical study of Cu(CO)3−

Photoelectron velocity map images of Cu(CO)3− have been experimentally recorded in the 700–1100 nm range. The infrared-inactive Cu-C symmetric stretching modes for Cu(CO)3 (v2 ≈ 367 cm−1) and Cu(CO)3− (v2 ≈ 408 cm−1), as well as the electron affinity (1.03±0.11 eV) of Cu(CO)3, are accurately determined from high resolution photoelectron spectra. In combination with quantum chemical calculations and bonding analyses, the coordination bonds in both Cu(CO)3− are Cu(CO)3 are found to be due to back-donation π bonding type, formed via electron promotion from Cu’s 4s orbital to the 4p orbital, which is consequently donated to the unoccupied anti-bonding π* orbitals of the carbonyl groups. The attachment of an additional electron to Cu(CO)3 strengthens the Cu-CO coordination, making Cu(CO)3− more stable. The intramolecular interactions between the Cu/Cu− and carbonyl groups are found to be primarily governed by electrostatic forces and orbital interactions.