Sub-nanometer clusters exhibit size-dependent properties unique from larger nanoparticles that do not scale predictably to the bulk phase. These size-tunable properties and the fact that most of their metal atoms are at their surfaces make clusters potentially transformational materials for improving the efficiency of chemical production, capturing and converting energy from the sun, and abating harmful atmospheric pollutants. In order for these exciting applications to become reality, it will be necessary to develop scalable methods for synthesizing clusters of predetermined size and composition for a specific function. While phosphines have been used for decades to promote the synthesis of gold clusters, it is not understood how the functional groups at coordinating phosphorus centers influence the size distributions and properties of ligated gold clusters. Using high mass resolution electrospray ionization mass spectrometry (ESI-MS) and collision induced dissociation (CID) we are characterizing the electronic and steric contributions of differently-functionalized phosphines to the size distributions, reactivity, and stability of gold clusters synthesized in solution. Quantitative ligand binding and cluster fragmentation energies, which determine the stability and size evolution of clusters during synthesis, are also determined using a unique surface induced dissociation (SID) experiment. The quantitative experimental results are compared to ligand binding energies determined with high-level theoretical calculations which allows benchmarking of the computational results. The surface immobilization and charge state of supported clusters, both of which have been shown to influence their properties, are also explored using soft landing of mass-selected ions (SL), a versatile and controlled approach to surface modification. This multifaceted approach enables characterization of a broad spectrum of phenomena in the cluster size regime where each-atom-counts toward determining properties.

Elucidating the role of ligand functionality in phosphine-protected gold clusters using mass spectrometry

2019 Fall National Meeting

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