Co⁺(C₂H₂) Complexes Studied with Selected-Ion Infrared Spectroscopy and Theory

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Metal-ligand interactions are crucial in catalysis and materials science.
• Understanding the initial binding configurations of small molecules to metal ions is fundamental.
• Acetylene (C2H2) is a key building block in organic synthesis.

Purpose of the Study:

• To characterize the structure of cobalt-acetylene (Co+(C2H2)n) complexes.
• To investigate the bonding interactions between Co+ and acetylene ligands.
• To determine the factors influencing the reactivity of acetylene ligands in these complexes.

Main Methods:

• Infrared photodissociation spectroscopy using argon tagging.
• Laser vaporization in a supersonic molecular beam for complex generation.
• Density functional theory (DFT) calculations for structural and energetic analysis.

Main Results:

• Infrared spectra indicate cation-π bonding configurations for unreacted Co+(C2H2)n complexes (n=1-6).
• Observed red shifts in C-H stretching frequencies are attributed to charge transfer from acetylene to Co+.
• Computational studies predict significant activation barriers for ligand coupling reactions, explaining the absence of reacted isomers.

Conclusions:

• Cobalt-acetylene complexes exist primarily as unreacted species due to kinetic inhibition.
• High activation energy barriers prevent exothermic reactions, such as benzene formation, in smaller clusters.
• The findings provide insights into the initial stages of metal-ligand interactions and reactivity.