Selenium hexafluoride

Selenium hexafluoride is the inorganic compound with the formula SeF₆. It is a very toxic colourless gas described as having a "repulsive" odor.^[5] It is not widely encountered and has no commercial applications.^[6]

Selenium hexafluoride

Names
IUPAC name Selenium hexafluoride
Other names Selenium(VI) fluoride, Selenium fluoride
Identifiers
CAS Number	7783-79-1 Y
3D model (JSmol)	Interactive image
ChemSpider	22964 N
ECHA InfoCard	100.149.506
PubChem CID	24558
RTECS number	VS9450000
UNII	H91D37I668 Y
CompTox Dashboard (EPA)	DTXSID00999041
InChI InChI=1S/F6Se/c1-7(2,3,4,5)6 N Key: LMDVZDMBPZVAIV-UHFFFAOYSA-N N InChI=1S/F6Se/c1-7(2,3,4,5)6 Key: LMDVZDMBPZVAIV-UHFFFAOYAP
SMILES F[Se](F)(F)(F)(F)F
Properties
Chemical formula	SeF6
Molar mass	192.9534 g/mol
Appearance	colourless gas
Density	7.887 g/L[1]
Melting point	−39 °C (−38 °F; 234 K)
Boiling point	−34.5 °C (−30.1 °F; 238.7 K) sublimes
Solubility in water	insoluble
Vapor pressure	>1 atm (20°C)[2]
Magnetic susceptibility (χ)	−51.0·10−6 cm3/mol
Refractive index (nD)	1.895
Structure
Crystal structure	Orthorhombic, oP28
Space group	Pnma, No. 62
Coordination geometry	octahedral (Oh)
Dipole moment	0
Thermochemistry
Std enthalpy of formation (ΔfH⦵298)	−1030 kJ/mol[3]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	toxic, corrosive
NFPA 704 (fire diamond)	3 0 0
Lethal dose or concentration (LD, LC):
LCLo (lowest published)	10 ppm (rat, 1 hr) 10 ppm (mouse, 1 hr) 10 ppm (guinea pig, 1 hr)[4]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 0.05 ppm (0.4 mg/m3)[2]
REL (Recommended)	TWA 0.05 ppm[2]
IDLH (Immediate danger)	2 ppm[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Structure, preparation, and reactions

SeF₆ has octahedral molecular geometry with an Se−F bond length of 168.8 pm. In terms of bonding, it is hypervalent.

SeF₆ can be prepared from the elements.^[7] It also forms by the reaction of bromine trifluoride (BrF₃) with selenium dioxide. The crude product can be purified by sublimation.

The relative reactivity of the hexafluorides of S, Se, and Te follows the order TeF₆ > SeF₆ > SF₆, the latter being completely inert toward hydrolysis until high temperatures. SeF₆ also resists hydrolysis.^[3] The gas can be passed through 10% NaOH or KOH without change, but reacts with gaseous ammonia at 200 °C.^[8]

Safety

Although selenium hexafluoride is quite inert and slow to hydrolyze, it is toxic even at low concentrations,^[9] especially by longer exposure. In the U.S., OSHA and ACGIH standards for selenium hexafluoride exposure is an upper limit of 0.05 ppm in air averaged over an eight-hour work shift. Additionally, selenium hexafluoride is designated as IDLH chemical with a maximum allowed exposure limit of 2 ppm.^[10]