Most, but not all, known compounds of hexacoordinate chalcogens (S, Se, Te) have all-trans geometries. Denney has reported3 the low-temperature syntheses of some thermally unstable tetrafluoropersulfuranes, R2SF4, including a few which were constrained to a cis geometry by a ring~ ystem.~ Cady reported4 the only previous example of a cis- persulfurane, SF4 (0SF5) 2, which was not thus constrained. There are no reported ...