Oxohalides and pseudohalides

Oxohalides and pseudohalides Table 16.7 Some physical properties of selenium oxohalides 

Property SeOFz SeOCh SeOBr2 Se02p2 (SeOF4)2 FjSeOF FjSeOOSFj 

SeOCh (Table 16.7) is a useful solvent it has a high dielectric constant (46.2 at 20°), a high dipole moment (2.62 D in benzene) and an appreciable electrical conductivity (2 x 10 ohm cm at 25°). This last has been ascribed to self-ionic dissociation resulting from chloride-ion transfer 2SeOCl2 f SeOCl+ -p SeOCb-. 

Two further oxofluorides of Se can be prepared by reaction of Se02 with a mixture of F2/N2 at 80° the main product is the hypofluorite FsSeOF whereas at 120° the peroxide FsSeOOSeFs predominates. The compounds (Table 16.7) can be purified by 

Direct fluorination of B(OTeF5)3 at 115° gives a 95% yield of the hypofluorite, FsTeOF, as a colourless gas which condenses to a colourless liquid below 0° and finally to a glass at about —80° the extrapolated bp is 0.6°. The chlorine derivative, ClOTeFs, the so-called teflic acid, HOTeFs, and the teflate anion, FsTeO (as caesium or tetraalkylammonium salts) are also useful synthons for a variety of metal derivatives, e.g. [Fe(OTeF5)3], [Nb(OTeF5)6]  

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