Self-assembly of trimesic acid (TMA) displayed remarkable abundance over its full coverage range on goldunder ultrahigh vacuum conditions. Experiments showed that previously well-reported “chicken wire” and“flower” structures were actually two special cases within its full coverage. All observed assembling structuresformed hexagonal porous networks that could be well-described by a unified model in which the TMAmolecules inside the half unit cells (equilateral triangles) were bound via trimeric hydrogen bonds and allhalf unit cells were connected to each other via dimeric hydrogen bonds. These porous networks possessedpores of 1.1 ± 0.1 nm in diameter, and the interpore distance was tunable from 1.6 nm on at a step size of∼0.93 nm. Energetics analysis unveiled that the assembling structures less than one molecular layer wasoptimally driven by maximization of the dimeric hydrogen bonds.