Formation of TPTA-NaCl/KCl Hybrid Nanostructures on Metal Surfaces

Alkali metal salts, as co-adsorbates, are crucial in regulating the self-assembly of molecules on metal surfaces. In this study, we report the self-assembled hybrid nanostructures formed by alkali metal salts (NaCl, KCl) and 2,2':6',2″-terpyridine-4,4',4″-tricarboxylic acid (TPTA) on Ag(111) and Cu(111) by a combined study of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. These hybrid structures exhibit distinct differences compared with the self-assembled structures of pure TPTA. Specifically, NaCl preferentially binds to the carboxylic groups of TPTA on Ag(111), but to the terpyridine core of TPTA on Cu(111). In contrast, KCl interacts with both the carboxylic groups and the terpyridine core of TPTA on Ag(111), but with only the carboxylic groups of TPTA on Cu(111). Furthermore, the co-deposited NaCl/KCl facilitates the deprotonation and hinders the decarboxylation of TPTA on Ag(111) as compared with the bare TPTA case, but only facilitates the deprotonation on Cu(111). Overall, our results demonstrate that the co-adsorption of specific alkali metal salts serves as an effective strategy to tune the binding modes and on-surface chemical reactions of molecules on different metal substrates.