Selenium and its compounds are on the Community Right-To-Know List.

OSHA PEL: TWA 0.05 ppm (Se)
ACGIH TLV: TWA 0.05 ppm (Se)
DFG MAK: 0.1 mg(Se)/m³
DOT Classification:  2.3; Label: Poison Gas

The Selenium hexafluoride, with the CAS registry number 7783-79-1, has the systematic name of hexafluoro-λ6-selane. And the molecular formula of this chemical is SeF₆. It is a colourless gas described as having a "repulsive" odor, and used as a electrical insulator.

Preparation of Selenium hexafluoride: It can be prepared from the elements or by the reaction of bromine trifluoride (BrF3) with selenium dioxide. And the crude product is purified by sublimation.

You should be cautious while dealing with this chemical. It is toxic by inhalation and if swallowed, and may cause burns. What's more, it has danger of cumulative effects. Therefore, you had better take the following instructions: When using, do not eat, drink or smoke; After contact with skin, wash immediately with plenty of ... (to be specified by the manufacturer); In case of accident or if you feel unwell, seek medical advice immediately (show label where possible).

You can still convert the following datas into molecular structure:
(1)SMILES: F[Se](F)(F)(F)(F)F
(2)InChI: InChI=1/F6Se/c1-7(2,3,4,5)6
(3)InChIKey: LMDVZDMBPZVAIV-UHFFFAOYAP

The toxicity data is as follows: