Article pubs.acs.org/JPCC
Organosoluble Au102(SPh)44 Nanomolecules: Synthesis, Isolation, Compositional Assignment, Core Conversion, Optical Spectroscopy, Electrochemistry, and Theoretical Analysis Milan Rambukwella,† Luca Sementa,‡ Giovanni Barcaro,‡ Alessandro Fortunelli,‡ and Amala Dass*,† †
Department of Chemistry and Biochemistry, University of Mississippi, Oxford, Mississippi 38677, United States CNR-ICCOM & IPCF, Consiglio Nazionale delle Ricerche, Pisa I-56124, Italy
‡
S Supporting Information *
ABSTRACT: Characterization of p-mercaptobenzoic acid (p-MBA) protected Au102(p-MBA)44 nanomolecules has been so far limited by its water-soluble ligand system. In this work we report the first synthesis and isolation of thiolateprotected organosoluble Au102(SPh-X)44 nanomolecules via one-phase synthesis. Monodispersity of the nanomolecules was confirmed from matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), and composition was determined from high-resolution electrospray ionization mass spectrometry (ESI-MS). For the first time we report the electrochemical behavior and temperature-dependent optical spectra of Au102(SPh)44. Theoretical simulations on the titled nanomolecules fully validate experimental data and demonstrate the role of electronic conjugation on optical properties.
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used. The synthesis,18 purification,19−22 and mass spectrometry of water-soluble nanomolecules is challenging, even though some progress has been made, and limits the wide adoption and analysis of this species among experimental chemists. Kornberg et al. first reported the crystal structure,7 followed by the synthesis, characterization,23 and optical spectroscopy24 of Au102(SC6H4COOH)44. The basis for ligand exchange on the 102-atom species was also reported.25 However, no other research team has accomplished the synthesis of this interesting Au102(SR)44 species, with any organosoluble ligand, to date. Investigation of redox behavior and low-temperature optical spectroscopy of the Au102 system was challenged by the lack of organosoluble Au102(SPhX)44 species. Extensive theoretical analysis has been performed on Au102(SC6H4COOH)44 due to the availability of the X-ray crystal structure. The stability of 102:44 species has been attributed to the 58 free electrons that are associated with a superatom electronic shell closure, with stable numbers corresponding to noble gas electronic configurations.10 Ab initio studies on a homologous Au102(SCH3)44 compound, including a comparison with Au 1 0 2 (SCH 3 ) 4 2 and Au104(SCH3)46 putative species, had previously been conducted by Zeng’s group,26 and it was suggested that the electronic shell closing of the effective 58 electrons accounts in part for the high stability of Au102(p-MBA)44. Density functional theory (DFT) calculations have being effectively used to understand
INTRODUCTION Gold nanomolecules1 are ultrasmall gold nanoparticles (
