Immobilization of Transition-Metal Complexes Onto Carbon Materials

3 METHODS FOR IMMOBILIZATION OF TRANSITION-METAL COMPLEXES ONTO CARBON MATERIALS 

Research on the immobilization of metal complexes using carbon materials is scarce compared with inorganic supports, such as zeolites, silicas, and clay-based materials [1-10]. Nevertheless, carbon materials are unique supports, as they can provide a variety of surface groups at the edges and/or defects of graphene sheets that can be tailored by adequate thermal or chemical treatments, besides the inherent chemical-physical reactivity associated with the graphene sheets themselves, which are hydrophobic, have low polarity, and have a rich n-electron density [13-15]. This can lead to a huge diversity of methods for immobilization of molecular species. 

We begin this section with the presentation of several methods for carbon snrface derivatization and then describe examples of immobilization of transition-metal complexes onto several carbons materials, exclnding fnllerenes and those nsed as electrode materials. 

Due to the nature of carbon materials, the presentation of representative methods for surface derivatization will follow an approach different from that described in the preceding section, which is based on the spatial target site where physical-chemical modification can take place (1) immobilization performed at edges and/or ends and defects of graphitic sheets, (2) immobilization onto the graphene sheets, and (3) exclusively for CNTs we present some examples of endohedral encapsulation of metal complexes. For the first two cases, covalent bonding and noncovalent interactions can occur directly between the transition metal complex and carbon supports or via spacers grafted to the carbon surface. 

Finally, the carbon surface oxygen groups can also be used for direct bonding to metal complexes, usually in the form of carboxylate and phenolate groups acting as ligands of their first coordination sphere (eovalent bond) or as counter ions for the complex (electrostatic interactions). 

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