Coverage dependent structures of oligopyridine adlayers on (111) oriented Ag films

Abstract

The coverage dependent formation of ordered structures in vapor deposited 2,4′-bis(terpyridine)derivatives (2,4′-BTP) on (111) oriented Ag films was investigated by STM. Following a two-dimensional (2D) disordered gas phase at lowest coverages, a sequence of at least three ordered structures is observed with increasing coverage. These include a ‘parallel chain structure’ (PCS), a ‘quasi-quadratic network’ (QQN) structure, and a ‘packed windmill structure’ (PWS), with ideal coverages of 0.37, 0.4, and 0.44 molecules nm⁻². At intermediate coverages between 0.37 and 0.44 molecules nm⁻², these structures coexist in larger islands. The energetics of the different phases, whose structures are mainly determined by attractive C–H⋯N bridges, are discussed in a picture including C–H⋯N and C–H⋯H–C interactions and lateral variations in the substrate–adsorbate interactions.