Two-dimensional (2D) molecular assemblies of 4',4 ''''-(1,4-phenylene)bis(2,2':61,2 ''-terpyridine) (PTPy) with several metal ions were investigated in 0.1 M HClO4 by cyclic voltammetry and electrochemical scanning tunneling microscopy (EC-STM). An STM image revealed that a disordered adlayer was deposited when iron ions were used, whereas well-ordered PTPy and gold complex adlayers were clearly observed when the electrode potential was precisely controlled. We succeeded in the direct formation of electrochemically active adlayers and the determination of the dependence of the electrocatalytic activity of 02 on the metal ion present.