Selenium compounds hexafluoride

Seiko Chemical Co., Ltd, 188 Selenium and Selenium Compounds, 115 Selenium dioxide, 116 Selenium hexafluoride, 116 Selenium oxychloride, 116 Selenium sulfides, 116... 

Note The REL and PEL also apply to other selenium compounds (as Se) except Selenium hexafluoride.]... 

Sihcon and boron bum ia fluorine forming siUcon tetrafluoride [7783-61-17, SiF, and boron trifluoride [7637-07-2] respectively. Selenium and tellurium form hexafluorides, whereas phosphoms forms tri- or pentafluorides. Fluorine reacts with the other halogens to form eight interhalogen compounds (see Fluorine compounds, inorganic-halogens). 

Tellurium Halides. Tellurium forms the dihalides TeCl and TeBi, but not Tel2. However, it forms tetrahalides with all four halogens. Tellurium decafluoride [53214-07-6] and hexafluoride can also be prepared. No monohalide, Te2X2, is believed to exist. Tellurium does not form well-defined oxyhalides as do sulfur and selenium. The tellurium halides show varying tendencies to form complexes and addition compounds with nitrogen compounds such as ammonia, pyridine, simple and substituted thioureas and anilines, and ethylenediamine, as well as sulfur trioxide and the chlorides of other elements. 

The ease with which selenium combines with many other elements to form binary compounds has already been mentioned (p. 299). Only one compound with hydrogen is known, but a series of polyselenides of the alkali metals corresponding to the polysulphides has been obtained. Selenium forms a hexafluoride, SeFG, but no other hexalialide has been isolated. The tetrahalides arc the most stable, and mixed chloro-bromides of quadrivalent selenium, SeCl Br, are known. Selenium monochloride, SeaCla, and selenium monobromide, Se2Br2, also exist as comparatively stable liquids at ordinary temperatures. No compound of selenium and iodine is known. Selenium oxychloride, SeOCl2, and the oxybromide, SeOBr2, are extremely reactive and useful compounds. 

Selenium hexafluoride, SeFg, the only clearly defined hexahalide, is formed by reaction of fluorine with molten selenium, It is more reactive than the corresponding sulfur compound, SFs, undergoing slow hydrolysis. Selenium forms tetrahalides with fluorine, chlorine, and bromine, and dihalides with chlorine and bromine. However, other halides can be found in complexes, e.g,. treatment of the pyridine complex of SeF/i in ether solution with HBr yields (py)2SeBrc Selenium tetrafluoride also forms complexes with metal fluorides, giving MSeF complexes with the alkali metals. 

All of these compounds are stable gases, exhibiting the maximum valency of the elements. They neither attack glass nor decompose spontaneously. The selenium and tellurium fluorides attack mercury making it adhere to glass, and m this respect they resemble (worn. Sulphur hexafluoride does not do this. 

Sulphur, selenium and tellurium all form the hexafluoride by direct combination other hexahalides are unknown. SFg and SeFg are chemically inert, colourless gases. The former is non-toxic and at once the most inert sulphur compound and possibly the most inert non-ionic fluorine compound it resists fused KOH. The somewhat more reactive SeF is reduced by NHg above 200"". TeFg, also a colourless gas, is hydrolysed by water ... 

ACGIH TLV (8-hour TWA) Selenium and compounds Selenium hexafluoride 0.2 mg/m3 0.16 mg/m3 ACGIH 2000... 

Washington HAP—threshold levels Selenium and compounds Selenium hexafluoride Selenium sulfides 0.5 tons/year 0.5 tons/year 0.5 tons/year BNA2001... 

The heavier elements of the group, S, Se and Te all form tetralluorides, EF4 and hexafluorides, EF6- If the central atom in these compounds form Lewis electron pair bonds to all the ligating fluorine atoms, it must accommodate five or six electron pairs in the valence shell, and we refer to the atoms as hypervalent. Sulfur forms no further homoleptic hypervalent derivatives. Selenium forms a solid tetrachloride, but as mentioned in the last paragraph, it decomposes on evaporation. Tellurium forms a solid tetrachloride, which may be evaporated without decomposition, as well as tetraphenyl-, tetramethyl- and hexamethyl- derivatives. 

Oxygen forms the compound OF2, but sulfur, selenium, and tellurium form the hexafluorides, XFg. Comment on this situation. What is the hybridization of the central atom in these compounds ... 

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