Self-Assembly of a Metal–Organic Framework by Stepwise Coordination of Carboxyl and Pyrrolyl Groups

The coordination abilities of different functional groups play fundamental roles in metal–organic frameworks. The coordination of indole-4-carboxylic acid with Fe on surfaces was investigated by scanning tunneling microscopy and density functional theory. The carboxyl group reacted with Fe atoms to form tetramers in a deprotonation process on Au(111) at room temperature. The deprotonation of pyrrolyl groups occurred at around 350 K, forming coordinated tetramer chains and rotiform structures. The arrangement of tetrameric clusters and coordination chains on Au(100) was influenced by surface reconstitution. A two-dimensional coordination network was obtained on Ag(111) without the influence of surface reconstitution.