Electron Microscopic Observation of an Icosahedral Au13 Core in Au25(SePh)18 and Reversible Isomerization between Icosahedral and Face-Centered Cubic Cores in Au144(SC2H4Ph)60

The atomic structures of Au-25( SC2H4Ph)(18), Au-25( SePh)(18), and Au-144(SC2H4Ph)(60), for which the crystal structures have been solved, were examined by aberration-corrected transmission electron microscopy (ACTEM). Time-lapse ACTEM images of Au-25(SePh)(18) exhibited characteristic patterns for the IhAu13 core more frequently compared to Au-25(SC2H4Ph)(18) at a dose rate (DR) = 4 pA/cm(2). In contrast, time-lapse images of Au-144(SC2H4Ph)(60) randomly showed two types of patterns for the Ih and fcc cores at DR = 4 pA/cm(2), indicating that Au-144(SC2H4Ph)(60) can be interconverted between the two isomeric forms without fragmentation. We proposed that the Ih isomer is more stable than the fcc isomer in Au-144(SC2H4Ph)(60) based on population analysis of the images of individual isomers.