Monosulfides

Monosulfides are binary compounds in which sulfur exists as the sulfide anion (S2−) bonded to a single metal or main‑group element, yielding an ideal metal-to-sulfur ratio of 1:1 (MS). The term is used in inorganic chemistry and mineralogy to distinguish these from disulfides (which contain S–S bonds) and polysulfides (S_n2− with n > 1).

In solid-state chemistry, many metal monosulfides crystallize in simple anion-adapted structures, such as the rock-salt or related lattices. Some monosulfides are non-stoichiometric minerals, where the metal site is partially vacant, giving compositions like Fe1−xS (pyrrhotite) that vary with formation conditions. The chemical properties of monosulfides depend on the metal, but they are generally ionic, have high melting points, and exhibit magnetic or semiconducting behavior in certain cases.

Common examples include iron(II) sulfide (FeS), nickel sulfide (NiS), manganese sulfide (MnS), cobalt sulfide (CoS), zinc sulfide (ZnS), and lead sulfide (PbS). These compounds are typically prepared by direct combination of the constituent elements at elevated temperature or by sulfiding oxides or other precursors. In many contexts, monosulfides are relevant in geology as ore minerals and in materials science as precursors or components of functional sulfide materials.

Reactions of monosulfides with acids can release hydrogen sulfide (H2S), a toxic gas, highlighting the need for appropriate safety precautions when handling these substances. See also disulfide, polysulfide, and metal sulfide.