Revealing the Character of Coordination Bonding in 2D Metal–Organic Frameworks

In this contribution, the coordination bond is investigated in a 2D metal-organic framework consisting of nickel and 7,7,8,8-tetracyanoquinodimethane (TCNQ) on a Ag(100) substrate. Using angle-resolved photoemission experiments supported by density functional theory calculations, the bonding is characterized as a result of the hybridisation between the ligand orbitals and the metal d-states. Unambiguous experimental fingerprints are presented for such a mechanism by revealing the splitting in energy of the frontier molecular orbitals into sets of bonding/antibonding states in the 2D metal-organic framework. Furthermore, a qualitative analysis of the energy level alignment is given for the transition metal inside the coordination environment and discuss the role of the network structure on the formation of such hybrid states.