The synthetic formation of mercury thiolates has been known for almost 200 years. These compounds are usually formed by a slow reaction of mercury salts with thiolates or disulfides to produce small (up to 1 mu m), plate-like crystals of Hg(S-R)(2). Herein we show that such mercury thiolates can be formed directly from liquid mercury via sonication with neat thiols. The process not only produces crystals very rapidly (within seconds) but also leads to the formation of large crystals (up to hundreds of micrometers). The high quality of these crystals enabled their detailed structural characterization, which showed that the crystals are composed of ordered Hg(thiol)(2) stacks. We extended the experimental procedure to form and characterize a range of Hg thiolate crystals with various chain lengths. We propose a new self-assembly mechanism that can explain how sonication which is usually used to break chemical bonds, to disperse materials, and to form nanosized crystallites-may lead to the growth of large, high-quality crystals.