Gold(I)sulfide

Gold(I) sulfide is the inorganic compound with the formula Au2S. It is one of two principal sulfides of gold. Gold sulfides exist in nature as solid solutions with silver, which has the same covalent radius.

Structure and preparation.
The compound crystallizes in the motif seen for cuprous oxide: gold is 2-coordinate, sulfur 4-coordinate, and the S-Au-S linkage is linear.[1] Linear coordination geometry is typically adopted by gold(I) compounds, such as the coordination complex chloro(dimethyl sulfide)gold(I).

It can be prepared by treating gold chloride with hydrogen sulfide[2] It also arises by treating dicyanoaurate:

H2S + 2 KAu(CN)2 → Au2S + 2 KCN + 2 HCN

This product is described as "initially dark reddish-brown" solid that turns "steel-gray.