Rhenium oxide fluorides

Rhenium oxide fluorides have not escaped activity concerned with... 

A. K. Brisdon, J. H. Jolloway, E. G. Hope, P. J. Townson, W. Levason, and J. S. Ogden, J. Chem. Soc., Dalton Trans., 3127 (1991). Ultraviolet-Visible Studies on Manganese and Rhenium Oxide Fluorides in Low-Temperature Matrices. 

There are five oxide fluorides of rhenium, ReOF4, ReOF3, ReOF5, ReC>2F3, and Re03F. Early reports of Re02F2 and ReOF2 (162, 163) have not been substantiated and must be considered doubtful. 

Most chemical properties of technetium are similar to those of rhenium. The metal exhibits several oxidation states, the most stable being the hep-tavalent, Tc +. The metal forms two oxides the black dioxide Tc02 and the heptoxide TC2O7. At ambient temperature in the presence of moisture, a thin layer of dioxide, Tc02, covers the metal surface. The metal burns in fluorine to form two fluorides, the penta- and hexafluorides, TcFs and TcFe. Binary compounds also are obtained with other nonmetaUic elements. It combines with sulfur and carbon at high temperatures forming technetium disulfide and carbide, TcS2 and TcC, respectively. 

One of the simplest oxides is the rhenium trioxide (ReOs) structure shown in figure lA(b). It consists of an incomplete fee host lattice of with Re in one-quarter of the octahedral sites. (Crystallographic shear (CS) phases (discussed in 1.10.5) based on ReOs may be considered as consisting of the cubic MO2 structure.) Many oxides and fluorides adopt the ReOs structure and are used in catalysis. 

It has been suggested (79) that polymorphism may occur for transition metal pentafluorides as it does for oxide tetrafluorides (91). X-Ray powder photographs of products from the reduction of hexafluorides in anhydrous hydrogen fluoride (79) showed that the samples of rhenium and osmium pentafluorides had different structures from those previously reported, but no unit-cell dimensions could be derived. 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

The NO + MF, (except NO -f WF,) reactions proceed spontaneously at 20°. The reactions were followed tensimetrically. Gaseous products were identified by infrared spectroscopy and the solid products were examined by. y-ray powder-photography. Both ReF, and OsF, formed NO+[MF,] (cub.) salts and neither salt could be induced to combine with more NO to yield the quadrivalent (NO),MF, compound. In their reactions with nitrosyl fluoride at 20°, however, the rhenium and osmium fluorides are clearly differentiated ReF, readily forms a thermally stable 2 1 adduct, which is isomorphous with (NOjjWFg, whereas the OsF, -i- ONF reaction is complex. The identification of small quantities of nitrogen oxide trifluoride, in the gaseous product of the reaction, indicate the existence of an... 

Although a number of complex fluorides of quinquevalent iridium, (e.g. KIrF,) are known, previous attempts to establish the simple fluoride have failed. The absence of a pentafluoride of iridium has become increasingly anomalous as the pentafluorides of the neighbouring elements, rhenium, osmium, and platinum have been prepared. Previous work - indicated that reactions which might have yielded the pentafluoride gave the tetrafluoride instead. The physical properties of this tetrafluoride. (m.p. 106—107 b.p. > 300 ), however, resembled those of a pentafluoride or oxide tetrafluoride. This indicated that iridium tetrafluoride differed structurally from its neighbouring tetrafluorides. 

The addition of oxygen anions (in the form of highly soluble calcium oxide or lithium and sodium oxides) in the NaCl-NaF eutectic melt containing rhenium leads to a decrease in the height of waves corresponding to the discharge of rhenium from the fluoride complexes, while at more negative potentials, two extra waves appear (Fig. 6a and 6b). 

We have studied the electrochemical behaviour of chloride, fluoride, and oxofluoride compounds of rhenium and established the conditions for the stabilization of Re(III), Re(IV), Re(VI), and Re(VII) complexes. For a more rigorous elucidation of interrelations between the redox potentials, the composition of melts, and the oxidation state of rhenium, it is necessaiy to undertake spectroelectrochemical investigations. Rhenium coatings with a thickness up to 2 mm on graphite and noble metal substrates were produced. 

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