Highly symmetric 2D rhombic nanoporous networks arising from low symmetry amphiphiles

Highly symmetric 2D nanoporous molecular networks containing rhombic voids are demonstrated to be accessible from low symmetry amphiphilic molecules. The amide amphiphiles overcome the barrier to symmetry generation in the two-dimensional crystal through forming an aggregate as a building block. This aggregate consists of three inequivalent amphiphiles that assemble to create 3- and 6-fold rotation axes through hydrogen bonding. In the 6-fold rotation axis, an unusual hydrogen bonding network, supported by high resolution scanning tunneling microscopy (STM) images and computation, is observed. This network formed by amide groups significantly contributes to constructing the rhombic nanoporous network, whereas carboxylic acid amphiphiles do not adopt this nanoporous network due to a geometric difference of hydrogen bonding. This investigation demonstrates that a high symmetry pattern is achievable without correlation with molecular symmetry through the proper combination of noncovalent interactions of simple amphiphilic molecules.