Mass Spectrometry of Ligand Exchange Chelation of the Nanoparticle [Au25(SCH2CH2C6H5)18]1− by CH3C6H3(SH)2

摘要

Mass spectrally detected products of ligand exchange reactions of the nanoparticle [Au₂₅(SC₂H₄C₆H₅)₁₈]1−, (abbrev. Au₂₅(SC₂Ph)₁₈), where the dithiol is toluene-3,4-dithiol, CH₃C₆H₃(SH)₂, include nanoparticles containing both doubly (bidentate, or chelating) and singly bonded dithiol. The bidentate binding displaces two of the original −SC₂Ph ligands, and singly bonded dithiol displaces one −SC₂Ph ligand, while maintaining, for mass spectrally detected species, occupancy of 18 ligation sites. Extended exchange reaction times result in an apparent maximum of six chelated dithiolates. In the Au₂₅(SC₂Ph)₁₈ nanoparticle, six semi-rings of −S(R)−Au−S(R)−Au−S(R)− act as the protecting ligand shell surrounding a Au₁₃ core; the chelation is suggested to involve binding of dithiolates to adjacent semi-rings, rather than to a single semi-ring. Both high resolution ESI and lower resolution MALDI spectra support the product assignments. A minor extent of bidentate ligand incorporation is sufficient to severely compromise the well-known Au₂₅(SC₂Ph)₁₈ UV−vis fine structure and to alter its voltammetric pattern, reflecting either associated semi-ring distortion and/or decay of the exchange product.