Hexahalides

The only hexahalides known are the colourless gaseous fluorides SeFg and TeFg and the volatile 

The mixed halides TeClFs and TeBrFs are made by oxidative fluorination of TeCU or TeBr4 in a stream of Fi diluted with N2 at 25°. Under similar conditions Tel4 gave only TeFg and IF5. TeClFs can also be made by the action of GIF on TcF4, TeCU or Te02 below room temperature it is a colourless liquid, mp —28°, bp 13.5°, which does not react with Hg, dry metals or glass at room temperature. 

Electron diffraction or microwave studies have shown that the molecules SFg, SeFg, TeFg, and also SFsCl and SFsBr have octahedral con-figurations-regular in the case of the hexafluorides  

data for this halide are consistent with a model consisting of two -SF5 groups joined in the staggered configuration so that the central S—S bond is collinear with two S-F bonds, with all interbond angles 90° (or 180°), S-F, 1-56 A, and S-S, 2-21 The length of the S-S bond may be due to repulsion of the F atoms. 

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The reaction must be carried out in the absence of direct sunlight, since sunlight causes direct addition of the halogen to the hydrocarbon, particularly if the latter is warm benzene, for example, yields the hexahalide ... 

Other series of mixed hexahalide complexes have been made. Thus from K2OsI6 and concentrated HBr ... 

Table VII. Crystal-Field Parameters for Hexahalide 5f -Actinide Ions.

Ge) for the electron diffraction measurements was carried out by thermal reaction of silicon (1200°C, 1 Torr) or germanium (620-660°C, 1 Torr) with the corresponding tetrahalides MX4 or hexahalides M2X6 (Shultz et al., 1979 Schultz et al., 1982 Hargittai et al., 1983). 

For molecules with low polarity like hydrocarbons, electrostatic forces have only a minor influence. Molecules with highly polar bonds behave as dipoles or multipoles and exhibit corresponding interactions. For instance, hexahalide molecules like WF6 or WC16 are multipoles, the halogen atoms bearing a negative partial charge -q, while the metal... 

The coordination chemistry of iridium has continued to flourish since 1985/86. All common donor atoms can be found bound to at least one oxidation state of iridium. The most common oxidation states exhibited by iridium complexes are I and III, although examples of all oxidation states from —I to VI have been synthesized and characterized. Low-oxidation-state iridium species usually contain CO ligands or P donor atoms, whereas high-oxidation-number-containing coordination compounds are predominantly hexahalide ones. 

Finally, it is of interest to compare the estimates of covalency contributions for Ir(IV) hexahalides deduced by Allen et al. (11) from spectroscopic data, with those obtained by Owen and Thornley (85, 86) from ESR results. These latter authors attributed the reduction of below the free-ion value, entirely to symmetry restricted covalency, deriving the expression 0bsd = N (Cd +s , >), where the normalising constant, N , is equal to (1 —4a S + and [Pg.153]

The strong absorptions of the complex technetium (IV) hexahalides (Fig. 10) can also be utilized for spectrophotometric determinations. A sensitive method has been developed using hexachlorotechnetate (IV) When pertechnetate is heated for 50- 0 min in cone, hydrochloric acid, it is reduced to the complex [TcClgp . The absorption curve of [TcClgf in cone. HCl has a maximum at 338 nm where technetium can be determined in the presence of microgram amounts of rhenium or molybdemun. The molar extinction coefficient is said to be 32.000 (after Jorgensen and Schwochau it amounts to 10.600). About 0.1 fig Tc/ml can be determined. Rhenium present in quantities up to 30 ng/ml has almost no influence on the determination of technetium. The error in the determination of the latter in the presence of molybdenum at a weight ratio of 1 1 is 1-2%. 

In addition to complexes containing the WO, W02 and WO3 structural units, the element shows quite a varied chemistry in this oxidation state, undoubtedly because the hexahalides are reasonably stable and give rise to a variety of substitution products of the type [WX6 L ] (n = 1-6). In addition, coordination numbers higher than six can also be obtained. WVI also shows considerable tendency to form bonds of order higher than one with good jz donor atoms such as S, Se, N, NR, CHR and CR. 

The three hexahalides WF6, WC16 and WBr6 are known and synthetic routes to their preparation are summarized in Table 1. WF6 is a colorless gas while WC and WBr6 are blue-black moisture sensitive solids. Under well-defined conditions, the octahedral hexahalides undergo substitution to give products ot the type [WX6 L ] (n —1-6). Mixed fluoro-chloro compounds have been reported to result from reaction of WCI6 with F2 or from WFfi with Me3SiCl.6... 

The hexahalide ions [MoF6]- and [MoCls]- form well-characterized compounds which are unstable towards hydrolysis. MoF6 readily accepts electrons to form [MoF6] ions and will... 

Sulphur Hexafluoride, SF6.—Sulphur hexafluoride, the first hexahalide to be discovered, is prepared by submitting sulphur to the action of fluorine in a copper tube. The issuing gas on condensation in a spiral tube of the same metal at —80° C. becomes partly solidified by allowing the solid to vaporise gradually and passing the vapours through potassium hydroxide solution and solid potassium hydroxide successively, the substance is rendered purer, complete purification being effected subsequently by re-solidification followed by fractional evaporation.4... 

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. 

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