Using Coordination Chemistry Concepts to Unravel Electronic Properties of SACs in Bidimensional Materials

Single atom catalysts (SACs) embedded in bidimensional (2D) materials are commonly viewed as chemically doped 2D systems whose electronic properties can be discussed in terms of solid state physics, where the doping atoms are perturbating agents to the semimetallic (graphene) or insulating (h-BN) character of the 2D material. In this Perspective, we present a different and closer viewpoint, where the SAC electronic properties are interpreted in terms of coordination chemistry concepts, as the transition metal (TM) atom is complexed by a giant macrocycle, which is the defective 2D layer. In the crystal/ligand field theories, both electrostatic and covalent interactions between SAC and the surrounding 2D material are accounted for defining the splitting and mixing of the TM d states. This analysis reveals the key role played by the type of 2D material not only in determining spin and charge of SAC but also in stabilizing several SAC oxidative states via charge delocalization for an enhanced catalytic activity.