A Simple Strategy for Obtaining Au38 Clusters Stabilized by Different thiols
Daniel Stellwagen 1,2 , Andrew weber 1, Challa S.S.R. Kumar 1*
Center for advanced Microstructures and Devices, Louisiana State University, Baton Rouge, LA 70806,
USA; Utrecht University, 3508 TC Utrecht, The Netherlands; ckumar1@lsu.edu
Ultrasmall (< 2nm), atomically monodisperse, clusters of gold protected by thiolate ligands are
gaining lot of prominence due to their promise in a number of applications in catalysis, biological
labeling, and nano-electronics. [1,2,3] Unlike larger gold colloids whose electronic properties resemble the
bulk state, gold clusters with a core diameter less than 2 nm are characterized by distinct quantum
confinement effects. As a result discrete electronic structure and molecular type properties such as
HUMO-LUMO transitions and intrinsic magnetism are observed.
A major challenge in gold cluster synthesis using wet chemistry is the ability to synthesize same
cluster size with different stabilizers. The obvious reason for this problem is that the nature of the
stabilizer influences the nucleation and growth processes and therefore influences both size of the
cluster as well stablizer. Using a well established ‘thiol-etching’ procedure [4], known to yield
Au38(SC12H25)24, we have investigated the influence of thiol on the etching process. A wide variety of
thiols, both aliphatic (CnH(2n+1)SH [n= 4,6,8,12,16]) and aromatic (4-tertbutyl benzylmercaptan) were
employed. The resulting thiol-capped gold clusters were analyzed with various techniques such as
MALDI, HR-TEM, UV-VIS, IR, WAXS and Sulfur K-edge XANES. Based on these analyses, we report
obtaining Au38 clusters stabilized by thiols, both aliphatic (CnH(2n+1)SH [n= 4,6,8,12,16]) and aromatic (4tertbutyl benzylmercaptan). More specifically, the synchrotron radiation-based small angle X-ray
scattering analysis provides a strong supporting evidence for cluster size in agreement with MALDI
analysis. However, on the contrary, it is very interesting to note that the HRTEM results indicate
systematic variation in cluster size with the chain length of the aliphatic thiols. It is obvious that for
ultrasmall metal clusters HRTEM size determination is not a reliable technique.
References:
[1] Angew. Chem. Int. Ed. 2010, 49, 1295-1298
[2] Nature Chemistry. 2010, 2, 329-334
[3] Nanoscale. 2010, 2, 343
[4] J. Phys. Chem. A 2009, 113, 4281-4284