Solvent induced polymorphism in supramolecular 1,3,5-benzenetribenzoic acid monolayers

This work presents a scanning tunneling microscopy (STM) based study of benzenetribenzoic acid (BTB) monolayer structures at the liquid-solid interface. On graphite(0001) the tailored molecules self-assemble into 2D supramolecular host systems, suitable for the incorporation of other nanoscopic objects. Two crystallographically different BTB structures were found - both hydrogen bonded networks. A specific structure was deliberately selected by solvent identity. One of the BTB polymorphs is a 6-fold chicken-wire structure with circular, approximately 2.8 nm wide cavities. The other structure exhibits an oblique unit cell and a different hydrogen bonding pattern. The large cavity size of the chicken-wire structure was made possible through comparatively strong 2-fold hydrogen bonds between carboxylic groups. In addition, the low conformational flexibility of BTB was supportive to combat the tendency for dense packing.