Tuning the properties of Pd nanoclusters by ligand coatings: Electronic structure computations on phosphine, thiol, and mixed phosphine-thiol ligand shells

Tuning the properties of palladium nanoparticles using different protecting ligand shells is an important step toward the application-orientated design of nanoparticles for nanoelectronics and catalysis. We present a density functional theoretical characterization of Pd-13 and Pd-55, metal cores protected by only thiol, only phosphine, and mixed phosphine-thiol ligand shells. We analyze the ligand contributions to the frontier orbitals and the charge redistribution between the ligand shell and the metal core and show that these properties control the values of the charging energy and the catalytic activity. The charge transfer character of the metal-ligand interaction is influenced by the presence of other ligands in the capping system indicating a cooperative effect in the ligand induced charge redistribution. Because of the interplay between the stabilization of the frontier orbital due to the contribution of the sulfur and the charge donation by the phosphine, the charging energy of the mixed phosphine-thiol protected cluster is larger than that of the only phosphine and the only thiol systems. The complementary point of view is adopted for rationalizing the catalytic properties of the clusters by analyzing the effect of the interaction with the metallic core on the properties of the ligand. The impact of solvation on the electronic structure of the ligand capped Pd-13 cluster is investigated by including explicitly a layer of water molecules in the model system.