Tailoring the Properties of Metallic Clusters by Ligand Coatings

Tuning the properties of metallic clusters using different protecting ligand shells is an important step toward the application-orientated design of nanoparticles for nano-electronics and catalysis. An attractive property of these materials is the ability to engineer ligand shells composed of different molecules that influence the electronic structure of the system due to their chemical interaction with the metal core. Sometimes properties are not simply additive, and cooperative effects emerge so that the presence of more than one ligand type in the ligand shell imparts novel properties to the nanoparticles. We theoretically investigate at the DFT level palladium and gold metal cores interacting with only-thiol, only-phosphine and mixed phosphine-thiol ligand shells. In this talk, we present some examples of how these capping systems affect structural, optical, magnetic and charging properties of metallic clusters. For Au11 and Au13, we show that ligation stabilizes structural isomers characterized by a flake geometry of the metal core, and they show different optical properties than isomers with a compact gold core. The magnetic ground state of small bare Pd13 clusters is a high spin state, nonet or septet depending on the structural isomer. We demonstrate that interaction with thiols and phosphines differently affect structure and magnetic ground state in these systems. The mixed ligand species Pd13(SCH3)6(PH3)6 shows multiple energetically accessible spin states and consequently an unusual thermal behaviour of the average magnetic moment. The charge transfer character of the metal-ligand interaction is studied in small Pd13 and truly nano-sized Pd55 ligand protected metal cores. We discuss cooperative effects in the ligand induced charge redistribution and demonstrate that the electron donor or acceptor character of the ligand molecules affects the energetics of charging processes