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Article

Reaction of Au₅₅(PPh₃)₁₂Cl₆ with Thiols Yields Thiolate Monolayer Protected Au₇₅ Clusters

Supporting Info

Ramjee Balasubramanian, Rui Guo, Allan J. Mills,^† and Royce W. Murray*

Contribution from the Kenan Laboratories of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599

J. Am. Chem. Soc., 2005, 127 (22), pp 8126–8132

DOI: 10.1021/ja050793v

Publication Date (Web): May 13, 2005

†

Department of Chemistry, University of Liverpool, Liverpool, U.K., L69 3BX.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, rwm@email.unc.edu

Abstract

This paper describes the reaction of the phosphine-protected Au nanoparticle Au₅₅(PPh₃)₁₂Cl₆ (1, “Au55”) with hexanethiol (2) and other thiols. The voltammetry of the reaction product 2 displays a well-defined pattern of peaks qualitatively reminiscent of Au₃₈ nanoparticles, but with quite different spacing (0.74 ± 0.01 V) between the potentials of initial oxidation and reduction steps (electrochemical gap). Correction of this “molecule-like” gap for charging energy indicates a HOMO−LUMO gap energy of about 0.47 V. Voltammetry of the products (3 and 4) of reaction of 1 with C₃H₇SH and PhC₂H₄SH, respectively, is similar. Laser desorption/ionization mass spectrometry (LDI-MS) shows that 2 contains a high proportion of a core mass in the 14−15 kDa range, which is proposed to be Au₇₅. UV−vis spectra of 2−4 are relatively featureless, similar to previous reports of thiolate-protected Au₇₅ nanoparticles. HPLC analysis of 2 shows a Au₇₅ content of ca. 73%; the electrochemical purity estimate is also high, about 55%. Combining the mass spectrometric result with thermogravimetric analysis of 2 leads to a preliminary formulation Au₇₅(SC₆H₁₃)₄₀. This Au₇₅ synthesis complements a previous Brust-type synthesis and is unusual in the apparent provocation in the reaction of an increase in core size.