Synthesis of Nanostructured Materials and Cluster-Assembled Materials
EMSL Project ID
25394
Abstract
This proposal is a continuation of research under EMSL User Proposal #21790. This program is focused on exploratory syntheses of anionic metal clusters based on our gas-phase studies.A long-standing objective of cluster science is to identify and synthesize highly stable clusters, and to exploit the often unique properties of these small aggregates, either as stand-alone units, or as building blocks for cluster-assembled materials. For example, clusters Au20 (Fig. 1) and Sn12 (Fig. 2) were recently produced in the gas phase by our group.1,2 These clusters are highly stable, and they possess extremely interesting properties. Au20 has an intriguing tetrahedral structure, and, perhaps more importantly, it is a semiconductor with a band gap around 1.77 eV. Sn12 has a cage-like structure, and magnetic transition metal atoms can be incorporated in the center of the Sn12 cage (Fig. 3).3 These M@Sn12 clusters may therefore represent the building blocks for the fabrication of novel alloys with tunable magnetic properties.
However, in order to exploit the anticipated novel chemical and optical properties of ultra-small clusters, an effective synthetic method has to be developed to produce bulk quantities of materials. We have previously shown that the tetrahedral Au20 can form in solution with eight PPh3 ligands4. However, only a mixed sample was obtained and the yield of the tetrahedral Au20 species was too low, preventing us from obtaining a purified sample. In a continuing effort to synthesize the tetrahedral Au20, we have recently devised a new synthetic strategy by exploring different ligands and nucleation conditions while monitoring the reaction process using high resolution electrospray mass spectrometry5. We have tested a series of diphosphines of the general formula, P(Ph)2(CH2)MP(Ph)2, where the two P atoms are separated by an alkyl chain with a number M of carbon atoms. We have found that those ligands with longer spacers (M ≥ 3) exhibit a high degree of size selectivity, giving rise to monodispersed, or nearly monodispersed Au nanoparticles. The synthetic methodology described here has several advantages compared to more commonly employed techniques. It is monophasic and employs only commercially available precursors. Thus, it should be possible to scale up to produce large quantities of the ultra small and monodispersed Au clusters.
Here, we propose to continue our work on ultra-small Au clusters, and we present a strategy to synthesize Au20. The proposed research fits well within EMSL's research program and EMSL's mission. The proposed synthesis of atomically controlled metal clusters has important repercussions in catalysis (e.g., nanogold), for sensing applications as well (M@Sn12 can be envisaged as nano-magnets with a highly reactive surface). The team is interdisciplinary, and relies on contributions and visits from external users. A number of other EMSL capabilities will also be needed, the photoelectron spectroscopy facility (Lai-Sheng Wang, K.M. Beck), the FT-ICR facility (Rui Zhang), Synthetic facility (Tim Hubler), single-crystal XRD facility (Michael R. Thompson), powder XRD facility (David E. McCready), tube-furnace and heating oven in EMSL 1421(John Hu), SEM facility (Bruce W. Arey), and TEM facility (Chongmin Wang). Moreover, the group has required computational support (J. Li) in the past, and will probably require additional support in the future.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-08-03
End Date
2008-08-12
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Pan LL, J Li, and LS Wang. 2008. "Low-Lying Isomers of the B9- Boron Cluster: The Planar Molecular Wheel Versus Three-Dimensional Structures." Journal of Chemical Physics 129(2):024302.