The nature of interfacial binding of imidazole and carbene ligands with M20 nanoclusters (M = Au, Ag and Cu) – a theoretical study

Abstract

To inspire more exciting developments in the design and advances of self-assembled monolayers (SAMs), the fundamental understanding of the nature of interaction between metal nanoparticles and certain functional groups is very crucial. In this work, the interactions of imidazole based organic ligands with metal clusters (M₂₀) were analyzed by using quantum theory of atoms in molecules (QTAIM) calculations and energy decomposition (EDA) techniques based on the orbitals optimized by density functional theory method (DFT). Imidazole (IMI) and carbene ligands (a-NHC and n-NHC) were considered for their interaction on the apex and face center position of the three different coinage metal clusters Au₂₀, Ag₂₀ and Cu₂₀. The adsorption energies indicated the following behaviour in those complexes: (1) ligands adsorbed on the apex-A position of M₂₀ clusters are more stable and less reactive, (2) the chemical stability of the carbene ligands is high, and (3) of the two NHCs considered here, our findings show a higher interfacial binding strength for a-NHC with M₂₀ surfaces. Natural population analysis showed the charge transfer from imidazole to M₂₀ with N–M coordination bonding and the existence of strong C–M covalent bonding for carbene-n,a-NHC–M₂₀-complexes. QTAIM calculations again confirmed the covalent interactions in the latter complexes. Furthermore, energy decomposition analyses were performed to obtain the energetic properties of bonding for all the complexes.