Synthesis and Characterizations of Gold Chalcogenolate-Protected Nanoclusters and Nonoparticles: Structural Analysis by 77SE and 125TE NMR
Tong, Yuye J.
The objective of this thesis is to study the synthesis and characterizations of gold nanoparticles (Au NPs) and nanoclusters (Au NCs) with different anchoring elements, S, Se, and Te. 77Se and 125Te both are nuclear magnetic resonance (NMR) active nuclei, thus their NMR spectroscopy can be used to detect structural information. The kinetically controlled synthetic methods of monodispersed Au NCs have been studied. After aging Au NCs for increments between 1 to 115 hours, the mixture of phenylethyl thiolate-protected NCs converted to monodispersed Au25(SCH2CH2Ph)18 NCs. However, the mixture of alkyl selenolate- and tellurolate-protected NCs turned into bulky NPs with strong surface plasmon peak on UV-Vis spectra after the aging process. The steric effects and electronegativity of the phenyl groups are believed to be the key factor, where benzene ring hinders the formation of Au-Au bond formation to grow into large NPs. Aum(L-Au-L)n structural model (L = Se or Te) was proposed for alkyl selenolate- and tellurolate-protected Au NPs, where only one type of L exists and the structural information was consistent with the single peak on 77Se and 125Te NMR spectra. We reported the one-phase synthesis of Au25(SePh)18 NCs, and two-phase synthetic route of Au18(SePh)14 NCs. This is the first time the structure of atomic precise Au25(SePh)18 NCs were investigated via 77Se NMR. The two 77Se NMR peaks with 1:2 integration ratio confirmed the computational model of the cluster motif as Au13(core)–PhSe(1)–Au–Se(2)Ph–Au–Se(1)Ph–Au13(core). 77Se NMR and 125Te can serve as a new and convenient tool to obtain the structural information of NPs and NCs
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