Structural Changes in Atomically Precise Ag₂₉ Nanoclusters upon Sequential Attachment and Detachment of Secondary Ligands.

Abstract

Elucidating the structural dynamics of ligand-stabilized noble metal nanoclusters (NCs) is critical for understanding their properties and for developing applications. Ligand rearrangement at NC surfaces is an important contributor to structural change. In this study, we investigate the dynamic behavior of ligand-protected [Ag₂₉(L)₁₂]^3- NC's (L = 1,3-benzenedithiol) interacting with secondary ligand 2,2'-[1,4-phenylenebis (methylidynenitrilo)] bis[benzenethiol] (referred to as <b>L'</b>). We specifically focus on the structural characteristics of NC-based adducts [Ag₂₉(L)₁₂]<b>L'</b>_n^3- where n ranges from 1 to 4. This is probed experimentally by using a combination of ultraviolet-visible (UV-vis) spectroscopy, high-resolution electrospray ionization mass spectrometry (ESI MS), and ion mobility mass spectrometry (IM MS) coupled with collision-induced dissociation (MS² IMS). Density functional theory (DFT) calculations infer comparatively weak noncovalent interactions between the NCs and attached secondary ligands consistent with the fragmentation behavior and experimentally determined collision cross-sections (CCSs), which show a monotonic CCS increase of [Ag₂₉(L)₁₂]<b>L'</b>_n^3- with an increasing number of <b>L'</b> (<i>n</i> = 1-4). From a detailed analysis of the predicted structures, we infer progressive expansion of the Ag-S staple framework of the precursor NC as secondary ligands are added. Interestingly, detachment of <b>L'</b> from gas-phase [Ag₂₉(L)₁₂]<b>L'</b>_n^3- by collisional heating yields structures which retain "footprints" of the detached secondary ligands on a millisecond time scale.