Subnanometer clusters exhibit size-dependent properties unique from larger nanoparticles and the bulk phase. These highly-tunable properties and their large surface-to-volume ratio make clusters promising materials for applications in catalysis, solar energy conversion, chemical detection, and molecular electronics. Since “each-atom-counts” toward their properties it is necessary to develop scalable methods for synthesizing clusters of predetermined size and composition in solution. Although phosphines have been used for some time to promote gold cluster synthesis, it is not understood how the functionality at phosphine centers affects the size and properties of ligated clusters. Using high-resolution analytical electrospray ionization mass spectrometry (ESI-MS) and collision induced dissociation (CID) we are characterizing the electronic and steric effects of differently-substituted phosphines on the distribution of gold cluster ions synthesized in solution. Quantitative ligand binding and cluster fragmentation energies, which determine the stability and size evolution of clusters during synthesis, are also being determined using surface induced dissociation (SID) in a custom-built Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR-MS). The results of Rice-Ramsperger-Kassel-Marcus (RRKM) based modeling of the SID data are compared to ligand binding energies determined using high-level theoretical calculations. In addition, the surface immobilization and charge reduction of ligated cluster ions, which are known to influence their properties, are being explored using soft landing of mass-selected ions (SL) in a unique cluster-deposition instrument. This multipronged mass-spectrometry approach enables characterization of a broad spectrum of relevant phenomena including synthesis, thermochemistry, surface immobilization, and reactivity. The insights obtained from this work aid the rational synthesis of clusters and with predetermined properties for a number of potential applications.

Synthesis, stability, and immobilization on surfaces of phosphine-ligated gold clusters

254th National Meeting (2017)

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