CO2 Binding and Induced Structural Collapse of a Surface-Supported Metal-Organic Network
Extensive efforts have been directed toward identifying catalytic material composites for efficiently transforming CO2 into valuable chemicals. Within this long-standing scientific challenge, the investigation of model systems is of particular interest to gain fundamental insight into the relevant processes and to synergistically advance materials functionalities. Inspired by the ubiquitous presence of metal organic active sites in the conversion of CO2 we study here the interaction of CO2 with a two-dimensional metal organic network synthesized directly on a metal surface as a model system for this class of compounds. The impact of individual CO2 molecules is analyzed using scanning tunneling microscopy supported by density functional theory calculations. Dosage of CO, gas to the thermally robust Fe-carboxylate coordination structure at low temperatures (100 K) leads to a series of substantial rearrangements of the coordination motif; accompanied by a collapse of the entire network structure. Several binding sites of weak and moderate strengths are identified for CO2 near the iron nodes leading to a moderate structural weakening of the existing coordination bonds in the adapted models with no indication of CO2 dissociation. The observations suggest a concerted reaction pathway involving both CO2 and ligand molecules starting at irregular coordination sites that may eventually lead to the collapse of the entire network structure. The electronic properties of the Fe atoms in the carboxylate environment are determinant for the response of the network toward CO2 which depends critically on the local coordination environment. The results highlight that finely tuned metal organic complexes and networks at surfaces present promising features to activate and transform CO2.