This study explores directed noncovalent bonding in the self-assembly of nonplanar aromatic carboxylic acids on metal surfaces for the purpose of developing design strategies to create 2D surface metal organic frameworks (SURFMOFs). The acid linkers used are ethene based and are typically employed in the synthesis of 3D MOF crystalline solids. The two-dimensional structures formed from these molecules on HOPG and Au(111) are studied by scanning tunneling microscopy (STM) in solution environment. The process of the monolayer formation and final surface linker structures are found to be strongly dependent on the combination of molecule and substrate used and are discussed in terms of intermolecular and molecule-substrate interactions, bonding geometry and symmetry of the acid molecules. In the case of the linker self-assembly on HOPG, the molecule-substrate interactions play a decisive role in the resulting surface structure. When the acid molecules are adsorbed on Au(111), the intermolecular interactions tend to dominate over the weaker molecule-substrate bonding. Additionally, the interplay of the π-π interactions and hydrogen bonding that direct the surface self-assembly on the different supports can be controlled by varying the linker solution concentration. This is particularly applicable for the case of the acid molecules adsorbing on the Au(111) substrate. The precise control over predesigned surface structures and orientation of the nonplanar aromatic carboxylic linkers opens up an exciting prospect for manipulating the direction of SURFMOF growth in 2 dimensions and potentially in 3D. Evidence of 2D SURFMOFs formation is demonstrated by STM imaging of the initial stages of coordination reactions between transition metal (+2) ions and preassembled carboxylic acid linker monolayers at the solution/solid interface.<br/>

Balancing noncovalent interactions in self-assembly of nonplanar aromatic carboxylic acid linkers at the solution/solid interface: Progress toward 2D SURFMOFs synthesis

2019 Spring National Meeting

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