# Why do thiols have such a propensity for bonding with mercury?

Historically, thiols $\\ce{-SH}$ were known as "mercapto-" due to their strong propensity to bond with mercury. Certain drugs still carry this designation, though [mercaptopurine](http://en.wikipedia.org/wiki/Mercaptopurine) has an $\\ce{=S}$ group instead of a thiol. What makes the thiol group bond so strongly with mercury in particular? Why don't alcohols make such a strong bond with $\\ce{Hg}$? If it's known, was there any historical reason why it was important to be able to "capture" mercury?