Mechanisms of N-Heterocyclic Carbene Complex Lattice Formation

N-Heterocyclic carbenes (NHCs) that have wingtip groups with low steric bulk, such as 1,3-dimethyl-benzimidazol-2-ylidene (NHCMe), form bis-complexes with metal atoms when they are deposited onto Au(111) surfaces in vacuo. These complexes self-assemble into three different lattices: a herringbone, a double-herringbone, and a chiral kagome lattice. The static properties of these lattices have been studied with scanning tunneling microscopy and ab initio theoretical methods. Dynamic processes including complex center displacement and hindered monomer motion have also been observed. Our results suggest that in addition to surface hopping, exchange processes are important, providing a facile mechanism for atom exchange between the overlayer and the metal. These dynamic processes are well-known from studies of metal epitaxy but have not previously been discussed in the context of NHC self-assembly.