Roseo cobaltic chloride

At the very end of the eighteenth century, Tassaert—a French chemist so obscure in the history of chemistry that his first name remains unknown—observed that ammonia combined with a cobalt ore to yield a reddish-brown product. This was most likely the first known coordination compound. Throughout the first half of the nineteenth century, many other, often beautifully crystalline examples of various cobalt ammonates were prepared. These compounds were strikingly colored, and the names given to them—for example, roseo-, luteo- (from the Latin luteus, meaning deep yellow ), and purpureocobaltic chlorides—reflected these colors. 

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