Determination of the structure and geometry of N-heterocyclic carbenes on Au(111) using high-resolution spectroscopy. Issue 3 (12th November 2018)

• Record Type: Journal Article
• Authors: Lovat, Giacomo; Doud, Evan A.; Lu, Deyu; Kladnik, Gregor; Inkpen, Michael S.; Steigerwald, Michael L.; Cvetko, Dean; Hybertsen, Mark S.; Morgante, Alberto; Roy, Xavier; Venkataraman, Latha
• Is Part Of: Chemical science. Volume 10:Issue 3(2019)
• Page Start: 930
• Page End: 935
• Publication Date: 2018-11-12
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c8sc03502d
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : The geometry and bonding of N-heterocyclic carbenes to metal surfaces depends on the substituents on the N-atoms. Abstract : N-heterocyclic carbenes (NHCs) bind very strongly to transition metals due to their unique electronic structure featuring a divalent carbon atom with a lone pair in a highly directional sp 2 -hybridized orbital. As such, they can be assembled into monolayers on metal surfaces that have enhanced stability compared to their thiol-based counterparts. The utility of NHCs to form such robust self-assembled monolayers (SAMs) was only recently recognized and many fundamental questions remain. Here we investigate the structure and geometry of a series of NHCs on Au(111) using high-resolution X-ray photoelectron spectroscopy and density functional theory calculations. We find that the N-substituents on the NHC ring strongly affect the molecule–metal interaction and steer the orientation of molecules in the surface layer. In contrast to previous reports, our experimental and theoretical results provide unequivocal evidence that NHCs with N-methyl substituents bind to undercoordinated adatoms to form flat-lying complexes. In these SAMs, the donor–acceptor interaction between the NHC lone pair and the undercoordinated Au adatom is primarily responsible for the strong bonding of the molecules to the surface. NHCs with bulkier N-substituents prevent the formation of such complexes by forcing the molecules into an upright orientation. Our work provides unique insights into the bonding and geometry of NHC monolayers; more generally, it charts a clear path to manipulating the interaction between NHCs and metal surfaces using traditional coordination chemistry synthetic strategies.