A double-chain structure was fabricated on Au (111) with a bromine-functionalized phenanthroline precursor. We reveal the competition between the on-surface metal-ligand coordination and C-C coupling of the precursor by scanning tunneling microscopy (STM) imaging and density functional theory (DFT) calculations at the molecular level. Our work provides an additional strategy for controlling the on-surface polymerization, which is of great relevance to the construction of novel nanostructures.