We have investigated the role played by the atomic structure and reactivity of the supporting Ag(111) and Cu(111) surfaces on the formation of 2D metal−organic networks (2D-MONs) involving metal adatom clusters spawned by these two surfaces. While the hexahydroxytriphenylene (HHTP) molecule forms complexes with Ag 3 and Cu 3 adatom clusters on, respectively, the Ag(111) and Cu(111) surfaces, an extended order is only observed in the 2D-MON on Ag(111). By combining scanning tunneling microscopy measurements, density functional theory calculations, and microscopy image simulations, we show that the formation of Ag−HHTP metal−organic complexes is structurally compatible with a periodic arrangement of HHTP on the Ag(111) surface. In contrast, on Cu(111), tightly bonded and localized Cu−HHTP motifs are stabilized by the interaction of Cu adclusters with HHTP. However, they cannot match the surface structure of Cu(111) to form an extended 2D-MON. We observed that the formation of large 2D-MON domains on a metallic surface is only possible when the periodicity of the adsorbed surface assembly is weakly perturbed by the addition of metal adclusters that reinforced the bonding.