Understanding the interaction between carboxylates and coinage metals from first principles

摘要

Carboxylate groups have recently been explored as a new type of ligand to protect superatomic copper and silver nanoclusters, but little is known of the interfacial structure and bonding. Here, we employ density functional theory to investigate the interfaces of a model carboxylate group, CH3COO, on the coinage metal surfaces and clusters. We found that mu(2)-CH3COO is the most preferred binding mode on the three M(111) surfaces (M = Cu, Ag, and Au), while mu(3)-CH3COO is also stable on Cu(111) and Ag(111). The saturation coverage was found to be about seven CH3COO groups per nm(2) for all surfaces. CH3COO has the strongest binding on Cu and weakest on Au. Moving from the flat surfaces to the icosahedral M-13 clusters, we found that the eight-electron superatomic [M-13(CH3COO)(6)](-) nanoclusters also prefer the mu(2)-CH3COO mode on the surface. The icosahedral kernel in [Cu-13(CH3COO)(6)](-) and [Ag-13(CH3COO)(6)](-) was well maintained after geometry optimization, but a larger deformation was found in [Au-13(CH3COO)(6)](-). Given the broad availability and variety of carboxylic acids including amino acids, our work suggests that carboxylate groups could be the next-generation ligands to further expand the universe of atomically precise metal clusters, especially for Cu and Ag.