In coordination chemistry, knowledge on the oxidation state of the central metal is a significant basis for the design and synthesis of novel complexes. We examined the mechanism of on-surface coordination bonding to d-block metals by investigating the coordination of the newly designed and synthesized 4-(3,3-dimethyl-2,3-dihydro-1H-indol-1-yl)­benzonitrile (IBN) ligand with Au adatoms on a Au(111) surface. The formation of mono-, di-, tri-, and tetra-IBN complexes of gold [Au–(IBN) n (n = 1, 2, 3, and 4)] and metal-free hydrogen-bonded IBN complexes on the Au surface was examined by scanning tunneling microscopy. The nature of the coordinated Au adatom was clarified by density functional theory calculations. The 5d z 2 pseudospheroidal orbital of the Au adatom is the predominant contributor to the Au–N coordination bond, and the Au(111) surface maintains a zero oxidation state of the Au adatom for coordination numbers n = 1, 2, 3, and 4. This on-surface control of the oxidation state of the Au adatom explains the different coordination numbers that were observed when Au adatoms coordinate to IBN molecules, together with an absence of variability in the electronic structures of the Au complexes as a function of their coordination number.