Cryo spectroscopy of N₂ on cationic iron clusters

Area of Science:

• Physical Chemistry
• Surface Science
• Computational Chemistry

Background:

• Iron clusters are crucial in catalysis and materials science.
• Understanding nitrogen molecule (N2) adsorption on metal clusters is key to nitrogen fixation.
• Previous studies lacked detailed structural information on N2 binding to iron clusters.

Purpose of the Study:

• To investigate the structural and electronic properties of iron cluster dinitrogen adsorbate complexes.
• To identify different nitrogen binding motifs on iron clusters using IR-PD spectroscopy.
• To explore the impact of N2 adsorption on the electronic spin states of iron clusters.

Main Methods:

• Infrared photodissociation (IR-PD) spectroscopy was used to probe iron cluster-N2 complexes.
• Density Functional Theory (DFT) modeling was employed to analyze experimental spectra and predict structures.
• Analysis focused on vibrational frequencies and band broadening to infer binding characteristics.

Main Results:

• IR-PD spectra showed characteristic bands for end-on N2 binding (μ1,end motif) between 2200-2340 cm⁻¹.
• DFT modeling supported an icosahedral Fe13+ core structure and revealed spin quenching upon N2 adsorption.
• Distinct spectral features indicated varied N2 binding motifs (end-on, side-on, tilted) and couplings, including pairwise equivalent N2 on Fe17+.

Conclusions:

• The study elucidates diverse N2 binding configurations on cationic iron clusters.
• Adsorption of N2 influences the electronic spin states of iron clusters, leading to spin quenching.
• IR-PD spectroscopy combined with DFT provides powerful insights into the structure and bonding of metal-ligand complexes.