Spectroscopic fingerprints of iron-coordinated cobalt and iron porphyrin layers on graphene

Achieving control in the design of monolayer 2D functional catalysts represents a significant challenge. If that challenge is surmounted, coordinated single-metal-atom sites can offer tailored electronic configuration, ligation geometries, chemical activity and selectivity, and stability. We report spectroscopic evidence of the formation of a 2D metal-organic framework supported by a single graphene sheet in which coordination among tetra-pyridyl porphyrins (TPyPs) is spontaneously obtained by exploiting single iron atoms. The spectroscopic characterization, together with ab initio methods, reveals that metal intermolecular coordination occurs via the terminal nitrogen atoms in the pyridinic residues of adjacent TPyPs. Interestingly, the peripheral coordination of metal atoms impacts the electronic configuration of the porphyrin's core. Due to the chemical stability of the graphene layer, its weak interaction with the metal-organic framework, and the known electrochemical activity of the latter, this system represents an optimal candidate for the design and engineering of prototype 2D electrocatalytic materials.