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

作者：Nimmala Praneeth Reddy; Yoon Bokwon; Whetten Robert L; Landman Uzi; Dass Amala^*

来源：Journal of Physical Chemistry A, 2013, 117(2): 504-517.

DOI：10.1021/jp311491v

The preparation of gold nanomolecules with sizes other than Au-23(SR)(18), Au-38(SR)(24), Au-102(SR)(44), and Au-144(SR)(60) has been hampered by stability issues and low yields. Here we report a procedure to prepare Au-67(SR)(35), for either R = -SCH2CH2Ph or -SC6H13, allowing high-yield isolation (34%, similar to 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-67(SR)(33) 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 (C-13 and H-1), and structural characteristics of the metal atom core were determined by powder X-ray measurements. Models featuring a Au-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 (similar to 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-67(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-LUMO gap (similar to 0.75 eV) is nearly double that of the larger Au-102 compound and it is much smaller than that of the Au-38 one. The intermediary status of the Au-67(SR)(35) nanomolecule is also reflected in both its optical and electrochemical characteristics.

• 出版日期2013-1-17