Phosphorus sesquisulfide

Phosphorus sesquisulfide is the chemical compound with the formula 43.

Depending on purity, samples can appear yellow-green to grey. The compound was discovered by G. Lemoine and first produced safely in commercial quantities in 1898 by Albright and Wilson. It dissolves in an equal weight of carbon disulfide (CS2), underscoring the remarkable ability of CS2 to dissolve sulfur-rich compounds.

This bicyclic heterocycle has C3v symmetry. It is a derivative of phosphorus (P4) by insertion of Sulfur atoms between three P-P bonds. The P-S and P-P distances are 2.090 and 2.235 Å, respectively.

Other phosphorus sulfides and selenides
Several molecular phosphorus sulfides are known in addition to P4S3: three isomers of P4S4, two isomers of P4S5, P4S6, P4S7, P4S8, P4S9, and P4S10. P4S2 is also known but is unstable > -30 °C.

P4Se3 and P4S3 adopt the same structures.

Applications
P4S3 is an intermediate in production of phosphorus pentasulfide (P4S10).

A 1:2 mixture, by weight, of P4S3 and potassium chlorate, together with other materials, comprises the heads of "strike-anywhere matches".