Multi-electron Reduction Capacity and Multiple Binding Pockets in Metal-Organic Redox Assembly at Surfaces

Area of Science:

• Surface Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Redox-active ligands enable single-site metal centers in coordination networks.
• Ligand design requires consideration of electron storage and metal-coordinating pockets.

Purpose of the Study:

• To synthesize a novel ligand, tetraethyltetra-aza-anthraquinone (TAAQ), for creating complex dinuclear metal centers.
• To investigate the redox properties and surface complexation behavior of TAAQ.

Main Methods:

• Cyclic voltammetry for redox analysis.
• X-ray photoelectron spectroscopy (XPS) for elemental analysis and chemical shifts.
• Scanning tunneling microscopy (STM) for structural characterization.
• Density functional theory (DFT) for computational analysis.

Main Results:

• TAAQ exhibits significant electron storage capacity, undergoing up to a four-electron reduction.
• TAAQ successfully complexes with iron (Fe) on an Au(111) surface, confirmed by XPS.
• STM reveals irregular metal-organic coordination structures, suggesting multiple binding motifs.
• DFT calculations support the existence of various stable Fe:TAAQ isomers.

Conclusions:

• TAAQ is a promising ligand for creating complex metal coordination structures.
• The observed structural irregularity is attributed to multiple energetically accessible binding configurations.
• This work advances the design of sophisticated metal-organic frameworks with tailored properties.