Substrate, Molecular Structure, and Solvent Effects in 2D Self-Assembly via Hydrogen and Halogen Bonding

Abstract

Recently, halogen···halogen interactions have been demonstrated to stabilize two-dimensional supramolecular assemblies at the liquid−solid interface. Here we study the effect of changing the halogen, and report on the 2D supramolecular structures obtained by the adsorption of 2,4,6-tris(4-bromophenyl)-1,3,5-triazine (TBPT) and 2,4,6-tris(4-iodophenyl)-1,3,5-triazine (TIPT) on both highly oriented pyrolytic graphite and the (111) facet of a gold single crystal. These molecular systems were investigated by combining room-temperature scanning tunneling microscopy in ambient conditions with density functional theory, and are compared to results reported in the literature for the similar molecules 1,3,5-tri(4-bromophenyl)benzene (TBPB) and 1,3,5-tri(4-iodophenyl)benzene (TIPB). We find that the substrate exerts a much stronger effect than the nature of the halogen atoms in the molecular building blocks. Our results indicate that the triazine core, which renders TBPT and TIPT stiff and planar, leads to stronger adsorption energies and hence structures that are different from those found for TBPB and TIPB. On the reconstructed Au(111) surface we find that the TBPT network is sensitive to the fcc-and hcp-stacked regions, indicating a significant substrate effect. This makes TBPT the first molecule reported to form a continuous monolayer at room temperature in which molecular packing is altered on the differently reconstructed regions of the Au(111) surface. Solvent-dependent polymorphs with solvent coadsorption were observed for TBPT on HOPG. This is the first example of a multicomponent self-assembled molecular networks involving the rare cyclic, hydrogen-bonded hexamer of carboxylic groups, R 6 6 (24) synthon.

Selective binding in different adsorption sites of a 2D covalent organic framework

“…2b; consistent with previous work, we identify these interactions through Cl⋯H distances that are shorter than the sum of the Cl and H vdW radii, as shown in Table S1 in the ESI. 24,35 † The electron density associated with the chlorine atoms in the TCB molecule is anisotropically distributed, as shown in Fig. S2.…”

“…22 Gas-phase density functional theory (DFT) calculations were carried out using Gaussian09. 23 In previous work, we compared the performance of a number of functionals and basis sets for calculations of self-assembled systems comprising X⋯H and X⋯X interactions, 24,25 and found that the combination of M06-…”

Halogen Bonding in Two‐Dimensional Crystal Engineering

“…[23] The fact that the surface and the solvent matters, and quite significantly so, was illustrated by comparison of self-assembly of 2,4,6-tris(4-iodophenyl)-1,3,5-triazine (2, inset Figure 3a) and 2,4,6-tris(4-bromophenyl)-1,3,5-triazine (3, inset Figure 3c) on HOPG and on Au(111). [24] It was originally intended that by changing the type of halogen, molecule-substrate interactions can be modulated, and thus one would observe differences in packing of these two molecules. However, both molecules formed similar close-packed assemblies on HOPG, which are stabilized by a combination of halogen···halogen interactions and halogen···H hydrogen bonds.…”

“…(f) DFT calculated model for the two-component monolayer showing co-adsorption of heptanoic acid. Reproduced from ref [24]. with permission from the American Chemical Society.…”

Concentration-Dependent Two-Dimensional Halogen-Bonded Self-Assembly of 1,3,5-Tris(4-iodophenyl)benzene Molecules at the Solid–Liquid Interface

“…53 Gatti et al observed that solvent molecules can sometimes interact with molecules without an alkyl chain and form a 2D bicomponent structure on Au(111). 54 In this paper the concentration-dependent self-assembly of 1,3,5-tris(4-iodophenyl)benzene molecules at the 1-phenyloctane/graphite interface is investigated. These molecules do not have alkyl chains.…”