A Quantum Alloy: The Ligand-Protected Au{sub 25-x}Ag{sub x}(SR){sub 18} Cluster
Recent synthetic advances have produced very small (sub-2 nm), ligand-protected mixed-metal clusters. Realization of such clusters allows the investigation of fundamental questions: (1) Will heteroatoms occupy specific sites within the cluster? (2) How will the inclusion of heteroatoms affect the electronic structure and chemical properties of the cluster? (3) How will these very small mixed-metal systems differ from larger, more traditional alloy materials? In this report we provide experimental and computational characterization of the ligand-protected mixed-metal Au{sub 25–x}Ag{sub x}(SC{sub 2}H{sub 4}Ph){sub 18} cluster (abbreviated as Au{sub 25–x}Ag{sub x}, where x = 0–5 Ag atoms) compared with the unsubstituted Au{sub 25}(SC{sub 2}H{sub 4}Ph){sub 18} cluster (abbreviated as Au{sub 25}). Density functional theory analysis has predicted that Ag heteroatoms will preferentially occupy sites on the surface of the cluster core. X-ray photoelectron spectroscopy revealed Au–Ag state mixing and charge redistribution within the Au{sub 25–x}Ag{sub x} cluster. Optical spectroscopy and nonaqueous electrochemistry indicate that Ag heteroatoms increased the cluster lowest unoccupied molecular orbital (LUMO) energy, introduced new features in the Au{sub 25–x}Ag{sub x} absorbance spectrum, and rendered some optical transitions forbidden. In situ spectroelectrochemical experiments revealed charge-dependent Au{sub 25–x}Ag{sub x} optical properties and oxidative photoluminescence quenching. Finally, O{sub 2} adsorption studies have shown Au{sub 25–x}Ag{sub x} clusters can participate in photomediated charge-transfer events. These results illustrate that traditional alloy concepts like metal-centered state mixing and internal charge redistribution also occur in very small mixed-metal clusters. However, resolution of specific heteroatom locations and their impact on the cluster’s quantized electronic structure will require a combination of computational modeling, optical spectroscopy, and nonaqueous electrochemistry.
- Research Organization:
- National Energy Technology Lab. (NETL), Pittsburgh, PA, and Morgantown, WV (United States). In-house Research; National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV (United States)
- Sponsoring Organization:
- USDOE Office of Fossil Energy (FE)
- DOE Contract Number:
- DE-FE0004000
- OSTI ID:
- 1129777
- Report Number(s):
- A-CONTR-PUB-028
- Journal Information:
- JOURNAL OF PHYSICAL CHEMISTRY C, Vol. 117, Issue 15
- Country of Publication:
- United States
- Language:
- English
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