From WCl6 and selenium Se-17(2+)(WCl6-)(2) is formed in a solid state reaction at 110 degrees C. The structure of the dark red crystals consists of Se-17(2+) polycations built of two seven membered Se rings in the chair confer mation connected by a Se-3 chain, and of distorted octahedral WCl6- anions. The two positive charges of each ion are formally localized on the two triply bound Se atoms. The structure of Se-17(2+) is closely related to that of the previously known S-19(2+).