Au sub(67)(SR) sub(35) Nanomolecules: Characteristic Size-Specific Optical, Electrochemical, Structural Properties and First-Principles Theoretical Analysis

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 117; no. 2; pp. 504 - 517-504-517
• Main Authors: Nimmala, Praneeth Reddy, Yoon, Bokwon, Whetten, Robert L, Landman, Uzi, Dass, Amala
• Format: Journal Article
• Language: English
• Published: 07.01.2013
• Subjects: Atomic beam spectroscopy; Atomic structure; Binding; Electronic structure; Electronics; Nanostructure; Optical properties; Similarity
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp311491v

The preparation of gold nanomolecules with sizes other than Au sub(25)(SR) sub(18), Au sub(38)(SR) sub(24), Au sub(102)(SR) sub(44), and Au sub(144)(SR) sub(60) has been hampered by stability issues and low yields. Here we report a procedure to prepare Au sub(67)(SR) sub(35), for either R = -SCH sub(2)CH sub(2)Ph or -SC sub(6)H sub(13), allowing high-yield isolation (34%, 10-mg quantities) of the title compound. Product high purity is assessed at each synthesis stage by rapid MALDI-TOF mass-spectrometry (MS), and high-resolution electrospray-ionization MS confirms the Au sub(67)(SR) sub(35) composition. Electronic properties were explored using optical absorption spectroscopy (UV-visible-NIR regions) and electrochemistry (0.74 V spacing in differential-pulsed-voltammetry), modes of ligand binding were studied by NMR spectroscopy ( super(13)C and super(1)H), and structural characteristics of the metal atom core were determined by powder X-ray measurements. Models featuring a Au sub(17) 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-) charge-state of the nanomolecule. The electronic structure is analyzed within the framework of a superatom shell model. Structurally, the Au sub(67)(SR) sub(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-LUMO gap (0.75 eV) is nearly double that of the larger Au sub(102) compound and it is much smaller than that of the Au sub(38) one. The intermediary status of the Au sub(67)(SR) sub(35) nanomolecule is also reflected in both its optical and electrochemical characteristics.