Metal sulfides, polysulfides, polyselenides and polytellurides Sulfides

    The group 1 and 2 metal sulfides possess the antifluorite and NaCl lattices respectively and appear to be typical ionic salts. However, the adoption of the NaCl lattice (e.g. by PbS and MnS) cannot be regarded as a criterion for ionic character.   Most d-block metal monosulfides crystallize with the NiAs lattice (e.g. FeS, CoS, NiS) or the zinc blende or wurtzite structure (e.g. ZnS, CdS, HgS). Metal disulfides may adopt the CdI₂ lattice (e.g. TiS₂ and SnS₂ with metal(IV) centres), but others such as FeS₂ (iron pyrites) contain [S₂]^2-  ions. The latter are formally analogous to peroxides and may be considered to be salts of H₂S₂.  The blue paramagnetic [S₂]^- ion is an analogue of the superoxide ion and has been detected in solutions of alkali metal sulfides in acetone or dimethyl sulfoxide. Simple salts containing [S₂]^_ are not known, but the blue colour of the silicate mineral ultramarine is due to the presence of the radical anions [S₂]^- and [S₃]^-