Mechanisms of N-Heterocyclic Carbene Complex Lattice Formation

Area of Science:

• Surface science
• Materials chemistry
• Supramolecular chemistry

Background:

• N-Heterocyclic carbenes (NHCs) with small wingtip groups, like 1,3-dimethyl-benzimidazol-2-ylidene (NHCMe), form bis-complexes with metals.
• These complexes deposit onto Au(111) surfaces under vacuum conditions.

Purpose of the Study:

• To investigate the self-assembly of NHC-metal complexes on Au(111) surfaces.
• To characterize the static and dynamic properties of the resulting lattices.
• To explore the mechanisms governing atom exchange between the overlayer and the metal surface.

Main Methods:

• Scanning tunneling microscopy (STM) for static property analysis.
• Ab initio theoretical calculations for structural and energetic investigations.
• Observation of dynamic processes like complex center displacement and hindered monomer motion.

Main Results:

• NHCMe-metal complexes self-assemble into three distinct lattices: herringbone, double-herringbone, and chiral kagome.
• Static properties of these lattices were determined using STM and theoretical methods.
• Dynamic processes, including surface hopping and exchange processes, were observed and analyzed.

Conclusions:

• Exchange processes are vital for atom exchange between the NHC overlayer and the gold surface.
• These dynamic mechanisms, previously noted in metal epitaxy, are significant in NHC self-assembly.
• The study provides new insights into the fundamental processes governing NHC self-assembly on metal surfaces.