Quantum sized, thiolate-protected gold nanoclusters

The scientific study of gold nanoparticles (typically 1-100 nm) has spanned more than 150 years since Faraday's time and will apparently last longer. This review will focus on a special type of ultrasmall (<2 nm) yet robust gold nanoparticles that are protected by thiolates, so-called gold thiolate nanoclusters, denoted as Lambda u(n)(SR)(m) (where, n and m represent the number of gold atoms and thiolate ligands, respectively). Despite the past fifteen years' intense work on Au-n(SR)(m) nanoclusters, there is still a tremendous amount of science that is not yet understood, which is mainly hampered by the unavailability of atomically precise Au-n(SR)(m) clusters and by their unknown structures. Nonetheless, recent research advances have opened an avenue to achieving the precise control of Au-n(SR)(m) nanoclusters at the ultimate atomic level. The successful structural determination of Au-102(SPhCOOH)(44) and [Au-25(SCH2CH2Ph)(18)](q) (q = -1, 0) by X-ray crystallography has shed some light on the unique atomic packing structure adopted in these gold thiolate nanoclusters, and has also permitted a precise correlation of their structure with properties, including electronic, optical and magnetic properties. Some exciting research is anticipated to take place in the next few years and may stimulate a long-lasting and wider scientific and technological interest in this special type of Au nanoparticles.