Non‐covalent Interactions and Charge Transfer between Propene and Neutral Yttrium‐Doped and Pure Gold Clusters

The dopant and size‐dependent propene adsorption on neutral gold (Au(n)) and yttrium‐doped gold (Au(n−1)Y) clusters in the n=5–15 size range are investigated, combining mass spectrometry and gas phase reactions in a low‐pressure collision cell and density functional theory calculations. The adsorption energies, extracted from the experimental data using an RRKM analysis, show a similar size dependence as the quantum chemical results and are in the range of ≈0.6–1.2 eV. Yttrium doping significantly alters the propene adsorption energies for n=5, 12 and 13. Chemical bonding and energy decomposition analysis showed that there is no covalent bond between the cluster and propene, and that charge transfer and other non‐covalent interactions are dominant. The natural charges, Wiberg bond indices, and the importance of charge transfer all support an electron donation/back‐donation mechanism for the adsorption. Yttrium plays a significant role not only in the propene binding energy, but also in the chemical bonding in the cluster‐propene adduct. Propene preferentially binds to yttrium in small clusters (n<10), and to a gold atom at larger sizes. Besides charge transfer, relaxation also plays an important role, illustrating the non‐local effect of the yttrium dopant. It is shown that the frontier molecular orbitals of the clusters determine the chemical bonding, in line with the molecular‐like electronic structure of metal clusters.