The Carbon Sulfide Anions (C₄S₄)²⁻ and β-(C₃S₅)<sup>2−

Abstract

Tetrathiosquarate (C₄S₄)²⁻ forms water soluble compounds of salt like character with the earth alkaline ions from Mg²⁺ to Ba²⁺. While Ca²⁺ and Sr²⁺ yield almost isotypic tetrahydrates M(C₄S₄)•4 H₂O, Mg²⁺ and Ba²⁺ show a different behaviour. For Mg²⁺ the formation of the discrete octahedral complex ions [Mg(H₂O)₆]²⁺ is observed. Ba²⁺ forms a double salt Ba₄K₂(C₄S₄)₅•16 H₂O under inclusion of the potassium ions for the starting compound K₂(C₄S₄)•H₂O. In all structures, the (C₄S₄)^2- ions almost fulfil<i> D_4h</i> symmetry despite small derivations from the ideal symmetry are generally observed caused by the coordination to the cations. Tetrathiosquarate (C₄S₄)^2- forms water soluble compounds of salt like character also with Mn²⁺ and Fe²⁺ ions. In both structures, water molecules are present as ligands and fill the coordination environment of the cations to octahedra. In the iron(II) salt [Fe(H₂O)₂](C₄S₄)•4H₂O, the Fe²⁺ ions are coordinated by two H₂O ligands and linked by bridging tetrathiosquarate ions to a one-dimensional strand. The Mn(II) salt [Mn₄(OH)₄(H₂O)₄](C₄S₄)₂ is made up of cube-shaped complexes [Mn(OH)₄(H₂O)₄]⁴⁺, which are connected by tetrathiosquarate ions to a two-dimensional network, in which O–H•••S and O–H•••O bridging bonds connect the layers to a three-dimensional structure. β-(C₃S₅)^2- turned out to be quite sensitive to oxidation, giving at room temperature in aqueous solution the (C₆S₁₀)^2- ion, which was isolated using Ca²⁺ and Sr²⁺ as [Ca(H₂O)₇](C₆S₁₀) and [Sr(H₂O)₈](C₆S₁₀)•H₂O. To further study the hydrolysis and oxidation processes, aqueous solutions of the potassium salt of β-(C₃S₅)^2- were brought to crystallization using tetraphenylarsonium chloride, [As(C₆H₅)₄]Cl. By this method, several hydrolysis and oxidation products of β-(C₃S₅)^2- could be trapped as the respective [As(C₆H₅)₄]⁺ salts. Under air, crystals of [As(C₆H₅)₄]₂(C₃S₅)•2H₂O could be isolated and crystals of [As(C₆H₅)₄](HC₃S₅), containing the monoprotonated form of (C₃S₅)^2-, were found. [As(C₆H₅)₄]₂(C₃S₆O₃)•3H₂O is the third isolated compound formed under air. The novel (C₃S₆O₃)^2- ion is built of a planar C₃S₅ moiety with a pyramidal SO₃ group attached to the outer S atom of the C₃S₅ group. Under exclusion of air [As(C₆H₅)₄](C₃S₄H) crystals were formed within few days. The anionic unit derives from (C₃S₅)^2- by a C−S bond cleavage and the substitution of the sulfur atom by a hydrogen atom under formation of a new C−H bond.