Steering Metal–Organic Network Structures through Conformations and Configurations on Surfaces

Abstract

Molecular adsorption conformations and arrangement configurations on surfaces are important structural aspects of surface stereochemistry, but their roles in steering the structures of metal–organic networks (MONs) remain vague and unexplored. In this study, we constructed MONs by the coordination self-assembly of isocyanides on Cu(111) and Ag(111) surfaces and demonstrated that the MON structures can be steered by surface stereochemistry, including the adsorption conformations of the isocyanide molecules and the arrangement configurations of the coordination nodes and subunits. The coordination self-assembly of 1,4-phenylene diisocyanobenzene afforded a honeycomb MON consisting of 3-fold (isocyano)3–Cu motifs on a Cu(111) surface. In contrast, geometrically different chevron-shaped 1,3-phenylene diisocyanobenzene (m-DICB) failed to generate a MON, which is ascribable to its standing conformation on the Cu(111) surface. However, m-DICB was adsorbed in a flat conformation on a Ag(111) surface, which has a larger lattice constant than a Cu(111) surface, and smoothly underwent coordination self-assembly to form a MON consisting of (isocyano)3–Ag motifs. Interestingly, only C3–Ag nodes with heterotactic configurations could grow into larger subunits; those subunits with heterotactic configurations further grew into Sierpiński triangle fractals (up to fourth order), while subunits with homotactic configurations afforded a triangular MON.

On‐Surface Synthesis of [3]Radialenes via [1+1+1] Cycloaddition

“…The T2 also shows surface adsorption‐induced chirality, S ‐T2 and R ‐T2, which randomly assemble into triangular networks via coordination with Ag adatoms in homotactic or heterotactic configurations (indicated by blue and white arrows in Figure 3b, respectively). These results reveal that one isocyano group of the DCDICB undergoes [1+1+1] cycloaddition to form the aza[3]radialene T2, whereas the other isocyano group coordinates to a Ag adatom to form triangular networks [44, 47] . It is noteworthy that a few oligomers containing multiple aza[3]radialene units were occasionally observed, randomly appearing at the edges of the triangular networks (Figure 3h, i).…”

“…These two interactions activate the DCICB isocyano group. In contrast, this electrostatic interaction is lacking in similar self‐assembled structures of the isocyanobenzene (ICB) precursor without chlorine substituents, which cannot undergo [1+1+1] cycloaddition [44, 47] . In addition, the calculated HOMO–LUMO gaps of ICB, DCICB, DCICB absorbed on Ag(111) (Figure S16) show that both the chlorine substituents and the Ag(111) surface bring the HOMO and LUMO of isocyanide closer in energy, increasing the rate of the cycloaddition reaction [9, 10] …”

“…These results reveal that one isocyano group of the DCDICB undergoes [1+1+1] cycloaddition to form the aza [3]radialene T2, whereas the other isocyano group coordinates to a Ag adatom to form triangular networks. [44,47] It is noteworthy that a few oligomers containing multiple aza [3]radialene units were occasionally observed, randomly appearing at the edges of the triangular networks (Figure 3h, i). Thus, aza [3]radialene T2 prefers to undergo coordination with Ag adatoms rather than [1+1+1] cycloaddition.…”

“…In contrast, this electrostatic interaction is lacking in similar self-assembled structures of the isocyanobenzene (ICB) precursor without chlorine substituents, which cannot undergo [1+1+1] cycloaddition. [44,47] In addition, the calculated HOMO-LUMO gaps of ICB, DCICB, DCICB absorbed on Ag(111) (Figure S16) show that both the chlorine substituents and the Ag(111) surface bring the HOMO and LUMO of isocyanide closer in energy, increasing the rate of the cycloaddition reaction. [9,10] For the synergistic reaction pathway, the DFT-calculated energy barrier for the formation of three CÀ C bonds formation is 1.06 eV (0.35 eV per CÀ C bond), [38] and the distance between the carbon atoms of adjacent isocyano groups changes synchronously from 3.17 Å in the IS to 2.20 Å in the TS.…”

“…We propose there are two possible reasons. First, T2 can coordinate with Ag regardless of homotactic or heterotactic configuration (Figure S19), [44,47] but cannot undergo [1+1+1] cycloaddition in the heterotactic configuration due to the steric hindrance effect (Figure S20). Secondly, compared with the precursor DCDICB, the lower diffusion of T2 would decrease the reaction rate of [1+1+1] cycloaddition.…”