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 (M) 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 Au, Ag and Cu. The adsorption energies indicated the following behaviour in those complexes: (1) ligands adsorbed on the apex-A position of M 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 M surfaces. Natural population analysis showed the charge transfer from imidazole to M with N-M coordination bonding and the existence of strong C-M covalent bonding for carbene-n,a-NHC-M-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.

K. R. G acknowledges the support by CSIC under JAE-DOC program 'Junta para la Ampliacion de Estudios cofinanciada por el FSE, and in part, by the Basque Departamento de Educacion, Universidades e Investigacion, the University of the Basque Country UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-02).

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