Oxofluorides

Several families of halogen oxides with X—F bonds exist FXO2 (X = C1, Br, I), FXO3 (X = C1, Br, I), F3XO (X = Cl, Br, I), F3XO2 (X = Cl, I) and F5IO the thermally unstable FCIO is also known. Their structures are consistent with the VSEPR model (17.26-17.31). 

Chloryl fluoride, FCIO2, is a colourless gas (bp 267 K) and can be prepared by reacting F2 with CIO2. It hydrolyses to HCIO3 and HF, and acts as a fluoride donor towards SbFs (equation 17.54) and a fluoride acceptor with CsF (equation 17.55). 

Perchloryl fluoride, FCIO3 (bp 226 K, Afi7°(298K) = —23.8kJmor ) is surprisingly stable and decomposes only above 673 K. It can be prepared by reaction 17.56, or by treating KCIO3 with F2. 

The compound FBrOs is one of only a few examples of bromine in oxidation state +7. It is made by treating K[Br04] with AsFg or SbFg in liquid HF. FBr03 is more reactive than FCIO3 and is hydrolysed more rapdily than 

FCIO3 by aqueous alkali at room temperature (equation 17.58). Unlike FCIO3, FBrOs acts as a fluoride acceptor (equation 17.59) to give tra w-[F2Br03] (17.32). 

Alkali attacks FCIO3 only slowly, even at 500 K. Perchloryl fluoride is a mild fluorinating agent and has been used in the preparation of fluorinated steroids. It is 

Rationalize each of the following structures in terms of the VSEPR model. 

Confirm that the [IOF5] ion (the stmcture is given above) has symmetry. 

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Table 1. Physical and Thermodynamic Properties of Helium-Group Gas Fluorides, Oxofluorides, and Oxides...

BiF3 is sometimes said to be infusible or to have mp at varying temperatures in the range 725-770°, but such materials are probably contaminated with the oxofluoride BiOF (p. 572). 

Sulfur forms two main series of oxohalides, the thionyl dihalides OS X2 and the sulfuryl dihalides 02S X2. In addition, various other oxofluorides and peroxofluorides are known (p. 688). Thionyl fluorides and chlorides are colourless volatile liquids (Table 15.14) OSBt2 is rather less volatile and is orange-coloured. 

E. Enoelbrecht and F. Sladky, Adv. Inorg. Chem. Radiochem. 24, 189-223 (1981). This review also includes oxofluorides of Se and Te, and related anions. 

Two further oxofluorides of Se can be prepared by reaction of Se02 with a mixture of P2/N2 at 80° the main product is the hypofluorite PsSeOP whereas at 120° the peroxide PsSeOOSePs predominates. The compounds (Table 16.7) can be purified by... 

This section considers compounds in which X (Cl, Br or I) is bonded to both O and F, i.e. F XOm. Oxofluorides -OF and peroxofluorides -OOF have already been discussed (p. 638) and halogen derivatives of oxoacids, containing -OX bonds are treated in the following section (p. 883). 

Although no OsFg has been described, there are oxofluorides in the +8 state. 

Experimental measurements of bond lengths support the formulation E=0 in oxohalides EOmX . In oxofluorides such as POF3, S02F2 and... 

The fact that most hypervalent molecules are fluorides or oxofluorides can be easily explained in terms of the three-centre bond approach. Crucial to the viability of the linear X-E-X moiety is the stabilisation of the nonbonding MO j2. This is optimised if X is relatively small in size... 

The fiercest fluorinating agents are appropriate for the oxidative preparation of a fluoride or oxofluoride, starting from a lower fluoride (or chloride, oxide etc.). Milder agents are preferred for non-oxidative preparations where, for example, Cl is displaced by F, e.g. ... 

Hydrolysis, yielding oxofluorides, oxides, and xenates, such as... 

The oxofluoride ONF3 is also known. Like NF4+ it is isoelectronic with N043- and must be described by a similar valence structure (3). N2F4 is interesting in that like N204 it readily dissociates into NF2 radicals. Double-bonded N2F2 exists in cis (4) and trans (5) forms, the former being thermodynamically more stable. 

The oxofluorides of osmium, amongst others, have recently been reviewed 731 we have already dealt with them on p. 584. 

For Se only Se02F2 is known. For Te there are no Te02X2 compounds, but recently TeOF2 and Te have been reported. The structure of TeOF2 is unknown but Te d has a complex polymeric structure. Both selenium and tellurium, as well as sulfur, form a number of more complex oxofluorides, a few of which are shown, with their structures, where known, in Table 12-7. 

There are also some derivatives of the oxofluorides with the ligand OTeF5" these are XeO(OTeF5)4 and Xe02(0TeF5)2. The only compound of Xe bound... 

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