Infra-red spectroscopy of size selected Au25, Au38 and Au144 ligand protected gold clusters

Abstract

Through the discovery of ligand protected metal clusters with cores of a precise number of atoms, the exploration of the third dimension of the periodic table for fundamental research and also for applications has become less remote. So far, the exact number of metal atoms in the core has been determined unambiguously only using mass spectrometry and single crystal X-ray diffraction. Gold clusters protected by 2-phenylethanethiol ligands, for instance, show distinct magic numbers that correspond to either electronic or geometric shell closings. For efficient control of their synthesis simple-to-use in situ spectroscopies are required. In the specific case of Au25(SCH2CH2Ph)18 clusters (1) we found a distinct shift of the aromatic C-H stretching band from 3030-3100 cm(-1) to below 3000 cm(-1) whose origin is discussed as an electronic interaction of the aromatic rings of the ligands with each other or with the gold core. This IR-feature is specific for Au25; the spectra of Au38(SCH2CH2Ph)24 (2) and Au144(SCH2CH2Ph)60 (3) clusters do not show this distinct shift and their IR-spectra in the C-H stretching regime are similar to that of the bare ligand. This significant change in the IR spectrum of Au25(SCH2CH2Ph)18 is not only of fundamental interest but also allows for in situ determination of the purity and monodispersity of the sample using FTIR spectroscopy during synthesis.

Insights into the Interface Between the Electrolytic Solution and the Gold Core in Molecular Au25 Clusters

“…[9][10][11][12][13] Insightsi nto the monolayer structure in solution have also been obtained by using IR and Raman vibrational spectroscopy methods. [13][14][15][16][17][18][19] Our recent studies point to electrochemically induced electront ransfer as ap articularly power-ful tool to understand how the clusterc ore interacts with the surrounding mediumt hrough an ot-so-shielding protective monolayer. [12] Historically,t he first clear-cut evidenceo ft he molecule-like properties of some MPCs was, indeed, provided by the observation of as triking core-size-dependent electrochemicalb ehavior.…”

Orientational changes of supported chiral 2,2′-dihydroxy-1,1′binaphthyl molecules

“…When depositing small metal clusters onto such surfaces it is assumed that the chirality is transmitted to the clusters as is the case for ligand protected clusters. [27][28][29] This combination of deposited metal clusters or nanoparticles with chiral molecules might however be crucial for triggering, for example, heterogeneous enantioselective catalysis under stable and well-defined conditions. Also, for the design of nonlinear chiroptical devices a deep insight into the link between the molecular origin of chiral effects, given by the molecular hyperpolarizability a (2) , and the macroscopic behaviour of these materials is of great scientific interest.…”

(Meta-)stability and Core–Shell Dynamics of Gold Nanoclusters at Finite Temperature

“…Transitionmetal nanoclusters typically exhibit catalytic activity at high temperature, 9 but gold nanoclusters have recently received special attention due to the discovery of their catalytic activity at low temperature. 10 Experimental and computational studies of both colloidal [11][12][13][14][15] and bare [16][17][18][19][20][21][22][23] gold nanoclusters have achieved important advances in the last decades. Most of the reported ab initio studies have been dedicated to searching for their putative global (energy) minimum configurations (pGMC) in the gas phase at zero temperature.…”