Sodium thioantimoniate

Structure

This hydrated salt consists of the tetrahedral SbS₄³⁻ anion (r_Sb-S = 2.33 Å) and sodium cations, which are hydrated. Related salts are known for different cations including ammonium and potassium.

The anhydrous salt is polymer with tetrahedral Na and Sb sites.

Preparation

Sodium thioantimoniate is prepared by the reaction of antimony trisulfide, elemental sulfur, and aqueous sulfide source.

3 Na₂S + 2 S + Sb₂S₃ + 9 H₂O → 2 Na₃SbS₄·9 H₂O

The sulfide can be generated indirectly by the thermal reaction of elemental sulfur with sodium hydroxide or even charcoal:

Sb₂S₃ + 8 NaOH + 6 S → 2 Na₃SbS₄ + Na₂SO₄ + 4 H₂O

In the latter route, a mixture of sodium sulfate (16 parts) is reduced by fusion with charcoal (4-5 parts) in the presence of antimony sulfide (13 parts). The melt is extracted into water which is treated with sulfur (4 parts). Upon evaporation of the solution, the salt crystallizes as large tetrahedra, which are easily soluble in water. The anhydrous salt melts easily on heating, and in the hydrated condition, on exposure to moist air becomes coated with a red film.

The required antimony(III) sulfide is prepared in the usual way by treatment of virtually any Sb(III) compound with sulfide sources:

2 SbCl₃ + 3 H₂S → Sb₂S₃ + 6 HCl

Reactions

The hydrate dissolves in water to give the tetrahydral SbS₄³⁻ ion. The salt gives "quinsulfide antimony," upon acidification:

2 Na₃SbS₄ + 6 HCl → Sb₂S₅ + 6 NaCl + 3 H₂S

Related compounds

Antimony (III) sulfide, Sb₂S₃