Gold and Alloy Nanomolecules: Synthesis, Ligand Induced Core Conversion, Characterization, and Atomic Structure

Gold nanoparticles have wide range of applications in the field of sensing, imaging, cancer therapy, and other biomedical applications. It is desired to have monodisperse and atomically precise gold nanoparticles to have better control and effective utilization of that nanoparticle. The nanoparticles that are less than 2 nm in size with precise number of atoms and ligands (± 0 atoms) which exhibit unique physical, chemical and optoelectronic properties are called as gold nanomolecules. This thesis presents the synthetic methodology and isolation of various monodisperse atomically precise nanomolecules and their characterization. UV-vis spectroscopy, Electrospray Ionization Mass Spectrometry (ESI-MS), Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS), Differential Pulse Voltammetry (DPV), and Single Crystal - X-ray diffraction (SC-XRD) are the commonly used characterization techniques for the analysis of nanomolecules. In this work, UV-vis spectroscopy, ESI-MS and MALDI-MS are the ones extensively used for the characterization. Thermochemical treatment of nanomolecules is a well-known technique for narrowing down the size distribution of a polydisperse crude mixture to obtain the most stable species. Au133(SPh-tBu)52 an ultra-stable nanomolecule was synthesized using the thermochemical treatment technique via core size conversion. The atomic structure of Au133(SPh-tBu)52 is found using SC-XRD. Theoretical analysis on the stability of Au133(SPh-tBu)52 over Au133(SPh)52 was also performed and concluded that the type of ligand plays a vital role in the formation of nanomolecules of specific sizes. Au36(SPh-X)24 is one of the widely studied small aromatic thiolate protected nanomolecules, however, there is a need for a straight forward and reproducible synthetic procedure. Hence, a large-scale synthetic protocol for the synthesis of monodisperse Au36 nanomolecule with a yield of ~42% (Au mole basis) was designed and time-consuming separation techniques such as size exclusion chromatography has been eliminated. Alloying of gold thiolate nanomolecules is an excellent way of tuning the unique properties of the monometallic counterparts. Au36-xAgx(SPh-tBu)24 was synthesized and characterized using UV-vis spectroscopy, ESI-MS and MALDI-MS spectrometry. Theoretical analysis was performed to predict the preferable sites of incorporation of silver atoms into the atomic structure of Au36(SPh-tBu)24 and it is concluded that the outer core sites are the kinetically favored sites for incorporation