Structural analysis of bulky thiolate-protected gold nanomolecules

Routine preparation of thiolate-protected gold nanomolecules involves, most commonly, straight-chain organic thiolate ligands for which the sulfhydryl `head' group is bound to a primary carbon atom. The primary connectivity of these sulfur atoms, such as for the case of n-hexanethiol and phenylethanethiol, allows for even packing, and the relative ease of formation of gold-thiolate oligomers about the surface monolayer in the formation of Au-SR bonds. Moreover, these straight-chain ligands routinely support the formation of an icosahedron-based series of core-size gold nanomolecules. Within this series of nanoparticles, Au25(SR)18 and Au38(SR)24 are among the most commonly studied core-sizes; Au25(SR)18 is situated upon an Au13 icosahedron, and Au38(SR)24 upon two face-fused icosahedra which share three gold atoms to give an Au23 core structure. The investigation of the experimental results presented by the student in this thesis outlines the alteration of these icosahedron-based core geometries. Specifically, by varying the steric hindrance of the --R group for which the sulfur head group is bound, a heightened gold:thiol ratio is achieved. With the application of bulky ligands, most notably tert-butanethiol and 1-adamantanethiol, the underlying geometry is altered such that face-centered cuboidal (fcc), octahedron-based structures are favored.;These structures are defined by atomic compositions, predicted by mass spectrometry and confirmed by X-ray Diffraction methods, for which a fewer number of sulfur ligands are needed to stabilize the overall structure. This is best illustrated in the case of the Au25(S-C2H4)18 and the Au30(S-t-C4H9)18 nanomolecules; because both have the same number of stabilizing ligands, it is clear that the addition of five gold atoms to the composition is accompanied by a structural alteration. In this work, the research and discussion focuses on the structural alteration associated with the 3-dimensional atomic arrangement in employment of bulky ligands, with experimentally-dervived data acquired from mass spectrometry, UV-visible spectroscopy, and single-crystal X-ray Diffraction.