Surface coordination chemistry of graphene: Understanding the coordination of single transition metal atoms

The recent advances in single-atom applications have shown that it is possible to manipulate the materials' properties by controlling its structure at the atomic level. Immobilization of single transition metal (TM) atom with catalytic, optical, electronic, or magnetic properties onto graphene supports is an outstanding research field. A similarity between graphene surface chemistry and the classical coordination chemistry is expected, and TM anchoring on the graphene can be view as the formation of a coordination complex. The possibility of tuning the electronic and chemical properties of graphene's coordination sites by varying its electron donor-receptor and hard-soft acid-base characteristics transforms graphene in a versatile and rich platform to pave the way for a deeper understanding of the surface coordination chemistry of other 2D materials. In this context, this review is focused on the latest advances on single atom functionalization (SAF) of graphene with transition metal ions, covering the synthesis, characterization, and its effects on graphene's physical and chemical properties. The fundamental aspects of the coordination chemistry, and how it is related to graphene's surface chemistry will be presented to give the basis to discuss the theoretical and experimental progress on graphene's SAF. A parallel between graphene solid-state physics theory and classical coordination chemistry, two areas that hardly influenced each other, will be done using concepts of ligand-field theory, Pearson's hard-soft acid-bases concept, and the molecular orbital theory of transition metal complexes. (C) 2020 Elsevier B.V. All rights reserved.