Thioselenide

A thioselenide is any organic chemical compound containing a selenium-sulfur bond.
Thioselenides are rare in nature, but have been identified, for example, in some species of "Allium" and in roasted coffee. The mammalian version of the protein thioredoxin reductase contains a selenocysteine residue which forms a thioselenide (analogous to a disulfide) upon oxidation.
The selenium-sulfur bond length is about 220 picometers.