Predicting Ligand Removal Energetics in Thiolate-Protected Nanoclusters from Molecular Complexes

Thiolate-protected metal nanoclusters (TPNCs) have attracted great interest in the last few decades due to their high stability, atomically precise structure, and compelling physicochemical properties, making them candidates for many applications, including biological labeling, sensing, and catalysis. TPNCs exhibit excellent catalytic activity for numerous reactions; however, recent work revealed that these systems must undergo partial ligand removal in order to generate catalytic active sites. Despite the importance of ligand removal on both catalysis and stability of TPNCs, the role of ligand and metal type on the ligand removal energetics is not well understood. Herein, we utilize Density Functional Theory to understand the energetic interplay between metal-sulfur and sulfur-ligand bond dissociation in metal-thiolate systems. We first probe 66 metal-thiolate molecular complexes (M-S-R) across combinations of M = Ag, Au, and Cu with twenty-two different ligands. Our results reveal that the energetics to break the metal-sulfur and sulfur-ligand bonds are strongly correlated and can be connected across all complexes through metal atomic ionization potentials. Moreover, we extend our work to experimentally relevant [M₂₅(SR)₁₈]^- TPNC, revealing the same correlations at the nanocluster level. Importantly, we unify our work by introducing a simple methodology to predict TPNC ligand removal energetics solely from calculations performed on metal-ligand molecular complexes. Overall, our model provides a screening tool to down-select ligand candidates exhibiting targeted ligand removal energetics, which is of paramount importance to TPNC catalysis. Thus, our results open new avenues toward accelerated TPNC catalyst design.