Polymorphism and metal-induced structural transformation in 5,5′-bis(4-pyridyl)(2,2′-bispyrimidine) adlayers on Au(111)

Abstract

Metal-organic coordination networks self-assembled on surfaces have emerged as functional low-dimensional architectures with potential applications ranging from the fabrication of functional nanodevices to electrocatalysis. Among them, bis-pyridyl-bispyrimidine (PBP) and Fe-PBP on noble metal surfaces appear as interesting systems to reveal details of molecular self-assembly and the effect of metal incorporation on the organic network arrangement. Here, we report a combined STM, XPS, and DFT study revealing polymorphism for bis-pyridyl-bispyrimidine adsorbed adlayers on the reconstructed Au(111) surface. The polymorphic structures are converted by the addition of Fe adatoms into one unique Fe-PBP surface structure. DFT calculations show that while all PBP phases exhibit similar thermodynamic stability, metal incorporation selects the PBP structure which maximizes the number of Fe-N close contacts. Charge transfer from the Fe adatom to the Au substrate and N-Fe interactions stabilize the Fe-PBP adlayer. The increased thermodynamic stability of the metal-stabilized structure leads to its sole expression on the surface.