Au67(SR)35 Nanomolecules: Characteristic Size-Specific Optical, Electrochemical, Structural Properties and First-Principles Theoretical Analysis

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• 作者：Praneeth Reddy Nimmala ; Bokwon Yoon ; Robert L. Whetten ; Uzi Landman ; Amala Dass
• 刊名：The Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：January 17, 2013
• 年：2013
• 卷：117
• 期：2
• 页码：504-517
• 全文大小：691K
• 年卷期：v.117,no.2(January 17, 2013)
• ISSN：1520-5215

文摘

The preparation of gold nanomolecules with sizes other than Au₂₅(SR)₁₈, Au₃₈(SR)₂₄, Au₁₀₂(SR)₄₄, and Au₁₄₄(SR)₆₀ has been hampered by stability issues and low yields. Here we report a procedure to prepare Au₆₇(SR)₃₅, for either R = 鈭扴CH₂CH₂Ph or -SC₆H₁₃, allowing high-yield isolation (34%, 10-mg quantities) of the title compound. Product high purity is assessed at each synthesis stage by rapid MALDI鈥揟OF mass-spectrometry (MS), and high-resolution electrospray-ionization MS confirms the Au₆₇(SR)₃₅ composition. Electronic properties were explored using optical absorption spectroscopy (UV鈥搗isible鈥揘IR regions) and electrochemistry (0.74 V spacing in differential-pulsed-voltammetry), modes of ligand binding were studied by NMR spectroscopy (¹³C and ¹H), and structural characteristics of the metal atom core were determined by powder X-ray measurements. Models featuring a Au₁₇ truncated-decahedral inner core encapsulated by the 30 anchoring atoms of 15 staple-motif units have been investigated with first-principles electronic structure calculations. This resulted in identification of a structure consistent with the experiments, particularly, the opening of a large gap (0.75 eV) in the (2鈭? charge-state of the nanomolecule. The electronic structure is analyzed within the framework of a superatom shell model. Structurally, the Au₆₇(SR)₃₅ nanomolecule is the smallest to adopt the complete truncated-decahedral motif for its core with a surface structure bearing greater similarity to the larger nanoparticles. Its electronic HOMO鈥揕UMO gap (0.75 eV) is nearly double that of the larger Au₁₀₂ compound and it is much smaller than that of the Au₃₈ one. The intermediary status of the Au₆₇(SR)₃₅ nanomolecule is also reflected in both its optical and electrochemical characteristics.