Supramolecular assembly of interfacial nanoporous networks with simultaneous expression of metal-organic and organic-bonding motifs.

The formation of 2D surface-confined supramolecular porous networks is scientifically and technologically appealing, notably for hosting guest species and confinement phenomena. In this study, we report a scanning tunneling microscopy (STM) study of the self-assembly of a tripod molecule specifically equipped with pyridyl functional groups to steer a simultaneous expression of lateral pyridyl-pyridyl interactions and Cu-pyridyl coordination bonds. The assembly protocols yield a new class of porous open assemblies, the formation of which is driven by multiple interactions. The tripod forms a purely porous organic network on Ag(111), phase α, in which the presence of the pyridyl groups is crucial for porosity, as confirmed by molecular dynamics and Monte Carlo simulations. Additional deposition of Cu dramatically alters this scenario. For submonolayer coverage, three different porous phases coexist (i.e., β, γ, and δ). Phases β and γ are chiral and exhibit a simultaneous expression of lateral pyridyl-pyridyl interactions and twofold Cu-pyridyl linkages, whereas phase δ is just stabilized by twofold Cu-pyridyl bonds. An increase in the lateral molecular coverage results in a rise in molecular pressure, which leads to the formation of a new porous phase (ε), only coexisting with phase α and stabilized by a simultaneous expression of lateral pyridyl-pyridyl interactions and threefold Cu-pyridyl bonds. Our results will open new avenues to create complex porous networks on surfaces by exploiting components specifically designed for molecular recognition through multiple interactions.