The ligand effect on the isomer stability of Au24(SR)20 clusters

Abstract

A key challenge in nanocluster research in particular and nanoscience in general is structure prediction for known compositions. Usually a simple ligand such as a methyl group is used to replace complex ligands in structure prediction of ligand-protected nanoclusters. However, how ligands dictate the energy landscape of such a cluster remains unclear. Here we elucidate the role of the ligand effect on the isomer stability of Au₂₄(SR)₂₀ nanoclusters by computing the relative energy of two isomers (one from the experiment, denoted as the “J” isomer; the other is the best theoretical model, denoted as the “P” isomer) of Au₂₄(SR)₂₀ with dispersion-corrected density functional theory. We find that when R = –CH₃, the two isomers are equally stable (within 0.13 eV), but for R = –CH₂CH₂Ph the P isomer is more stable by 1.6 eV and for R = –CH₂Ph-^tBu the J isomer is more stable by 1.0 eV. Partition of the total energy into DFT and vdW contributions indicates that the higher stability of the P isomer in the case of R = –CH₂CH₂Ph stems from the stronger vdW interactions among –CH₂CH₂Ph groups, while the higher stability of the J isomer in the case of R = –CH₂Ph-^tBu is due to its better capacity to respond to the steric effect of the larger –CH₂Ph-^tBu groups. This finding confirms that the ligand plays a crucial role in dictating the isomer stability.